Electrodiagnostic Technician (EDT) Certification — Questions and Answers

Question 1: Which EMG finding is most characteristic of chronic denervation with reinnervation?

Small, short-duration polyphasic MUPs
Fibrillations with normal MUP morphology
Large amplitude, long-duration polyphasic MUPs with reduced recruitment (Correct answer)
Early recruitment with normal MUP size

Correct answer: Large amplitude, long-duration polyphasic MUPs with reduced recruitment

Chronic denervation with reinnervation produces large-amplitude, long-duration polyphasic MUPs due to collateral sprouting and motor unit enlargement.

Question 2: An EMG machine displays 'impedance mismatch' between E1 and E2. Which of the following is the most likely consequence if recording proceeds without correction?

Higher CMAP amplitude due to reduced signal cancellation
Shorter latencies due to faster signal transmission
Stimulus artifact is eliminated
Increased common-mode noise and degraded signal quality (Correct answer)

Correct answer: Increased common-mode noise and degraded signal quality

Unequal electrode impedances degrade the differential amplifier's common-mode rejection, allowing more noise into the recording.

Question 3: What type of stimulus is used to elicit pattern-reversal visual evoked potentials?

An auditory tone burst at a fixed frequency
Electrical stimulation of the retina
A checkerboard pattern that alternates black and white squares at a set rate (Correct answer)
A single brief flash of white light

Correct answer: A checkerboard pattern that alternates black and white squares at a set rate

Pattern-reversal VEPs use a contrast-reversing checkerboard that produces more reproducible and reliable responses than flash stimuli.

Question 4: When documenting nerve conduction study results, which parameter is most critical to report for evaluating axonal integrity?

Skin temperature at the time of testing
Amplitude of the evoked potential (Correct answer)
Conduction velocity only
Peak latency and amplitude together

Correct answer: Amplitude of the evoked potential

Amplitude of the evoked potential (CMAP or SNAP) directly reflects the number of functioning axons and is the critical parameter for assessing axonal integrity.

Question 5: Which sweep speed is most appropriate for displaying motor unit potential (MUP) morphology during needle EMG?

500 ms/division
1 ms/division
100 ms/division
10 ms/division (Correct answer)

Correct answer: 10 ms/division

A sweep speed of 10 ms/division provides sufficient time resolution to assess MUP duration, amplitude, phases, and turns without compressing or stretching the waveform.

Question 6: Which layer of a peripheral nerve surrounds individual axons?

Epineurium
Perineurium
Endoneurium (Correct answer)
Myelin sheath

Correct answer: Endoneurium

The endoneurium is the innermost connective tissue layer that directly ensheathes each individual nerve fiber.

Question 7: In HIV-infected patients, the most common EDX pattern of peripheral neuropathy is:

Motor neuropathy with preserved sensory NCS
Demyelinating neuropathy similar to CIDP
Normal EDX throughout all stages of HIV
Distal sensory polyneuropathy with length-dependent SNAP amplitude reduction, related to HIV itself or antiretroviral toxicity (Correct answer)

Correct answer: Distal sensory polyneuropathy with length-dependent SNAP amplitude reduction, related to HIV itself or antiretroviral toxicity

Distal sensory HIV neuropathy (DSP) is the most common neuropathy in HIV, presenting as length-dependent axonal sensory-predominant polyneuropathy affecting sural SNAP earliest.

Question 8: In the 10-20 electrode placement system, where is the Oz electrode positioned for VEP recordings?

Occipital midline, 10% of the nasion-inion distance above the inion (Correct answer)
Frontal midline at the hairline
Vertex (top of the skull)
Right occipital region lateral to midline

Correct answer: Occipital midline, 10% of the nasion-inion distance above the inion

Oz is the midline occipital electrode in the 10-20 system and is the primary recording site for VEPs because it overlies the primary visual cortex.

Question 9: In a sensory nerve conduction study, which parameter is most sensitive for detecting early axonal loss?

Conduction velocity
Amplitude of the SNAP (Correct answer)
Distal latency
F-wave latency

Correct answer: Amplitude of the SNAP

SNAP amplitude is the most sensitive indicator of axonal loss because it directly reflects the number of functioning sensory axons.

Question 10: In suspected myasthenia gravis, what is the most sensitive EDX test?

Single-fiber EMG (SFEMG) (Correct answer)
Routine motor NCS
Standard needle EMG
Repetitive nerve stimulation at 50 Hz

Correct answer: Single-fiber EMG (SFEMG)

Single-fiber EMG, which measures jitter (variability in fiber discharge timing within a motor unit), is the most sensitive EDX test for neuromuscular junction disease including myasthenia gravis.

Question 11: A patient reports a latex allergy before the start of an electrodiagnostic study. What is the most appropriate immediate action?

Postpone the study until the allergy is medically treated
Use extra alcohol wipes to neutralize any latex residue
Proceed normally as latex is not used in EDX equipment
Verify that all supplies (gloves, electrode adhesives) are latex-free before proceeding (Correct answer)

Correct answer: Verify that all supplies (gloves, electrode adhesives) are latex-free before proceeding

Latex can be present in gloves and some electrode adhesives; confirming all materials are latex-free is mandatory to prevent anaphylaxis.

Question 12: During needle EMG, the sweep speed is typically set to which value for evaluating motor unit action potential (MUAP) morphology?

10 ms/div (Correct answer)
1 ms/div
500 ms/div
100 ms/div

Correct answer: 10 ms/div

A sweep speed of 10 ms/div provides adequate resolution to visualize the duration and morphology of individual MUAPs.

Question 13: In athletes with suspected nerve entrapment, EDX findings may be subtle because:

EDX equipment cannot be used on athletes
Physical training eliminates all neuropathy risk
Athletes are immune to nerve entrapment
Increased muscle mass and better collateral circulation may support higher baseline amplitudes, masking mild amplitude reductions (Correct answer)

Correct answer: Increased muscle mass and better collateral circulation may support higher baseline amplitudes, masking mild amplitude reductions

Well-conditioned athletes may have higher baseline CMAP and SNAP amplitudes; a relative amplitude reduction that is still within population norms may represent significant pathology for that individual.

Question 14: A patient's median sensory SNAP is absent at the wrist but present with near-nerve recording. This most likely indicates:

Submaximal stimulation artifact
Low-amplitude signal below surface electrode threshold, not true absence (Correct answer)
Martin-Gruber anastomosis
Complete axonal loss of sensory fibers

Correct answer: Low-amplitude signal below surface electrode threshold, not true absence

Near-nerve needle recording is far more sensitive than surface electrodes; a signal present only with near-nerve recording indicates a very low-amplitude potential, not true absence of sensory axons.

Question 15: The minimum skin temperature recommended for routine nerve conduction studies in the upper extremity is:

32°C (Correct answer)
25°C
37°C
20°C

Correct answer: 32°C

The minimum recommended skin temperature for upper extremity NCS is 32°C (with lower extremity at 30°C) to ensure accurate conduction velocity measurements.

Question 16: When applying surface electrodes for an EMG study, which skin preparation step is most critical for obtaining low-impedance recordings?

Applying electrode gel without abrasion
Warming the skin with a heat lamp for 10 minutes
Lightly abrading the skin with fine sandpaper or abrasive pad (Correct answer)
Shaving the area and applying alcohol only

Correct answer: Lightly abrading the skin with fine sandpaper or abrasive pad

Light skin abrasion removes the high-resistance dead-cell layer of the stratum corneum, reducing inter-electrode impedance to acceptable levels (below 5 kΩ).

Question 17: What is the primary reason for instructing a patient to remove all metal jewelry and watches before an electrodiagnostic study?

Jewelry can be magnetized by the stimulator and become a projectile hazard
Metal objects cause signal interference with the amplifier's A/D converter
Metal jewelry significantly increases body impedance and prevents electrode adhesion
Metal can concentrate electrical current and cause skin burns or arcing at the contact site (Correct answer)

Correct answer: Metal can concentrate electrical current and cause skin burns or arcing at the contact site

Metal objects can concentrate electrical current at contact points with skin, potentially causing focal burns or discomfort, particularly near the stimulation site.

Question 18: What is the first step when setting up an EMG machine?

Select waveform display
Insert electrode needles
Adjust audio output
Verify grounding and power connections (Correct answer)

Correct answer: Verify grounding and power connections

The very first step when setting up any electrodiagnostic (EDX) equipment, including an EMG machine, is to verify proper grounding and power connections. This is a critical safety measure to protect both the patient and the technician from electrical hazards. Ensuring stable power also prevents artifacts and ensures the reliable operation of the sensitive equipment.

Question 19: A patient with hepatitis C is scheduled for needle EMG. What is the correct needle handling protocol?

Use disposable single-use needles and discard in an approved sharps container immediately after use (Correct answer)
Reusable needles are acceptable if autoclave-sterilized between patients
Sterilize the needle in alcohol between muscles to save costs
Wear double gloves but standard disposal in regular waste is acceptable

Correct answer: Use disposable single-use needles and discard in an approved sharps container immediately after use

Single-use disposable needles eliminate cross-contamination risk and must be discarded immediately into a puncture-resistant sharps container per OSHA bloodborne pathogen standards.

Question 20: Which statement correctly describes the handling of a needle stick injury sustained during needle EMG?

Apply a tourniquet proximal to the puncture site and proceed to the ER
Swab the puncture with alcohol and continue the study if the patient is low-risk
No action is required if the needle was in use for less than 30 seconds
Squeeze the wound to express blood, flush with water, report to occupational health, and follow institutional exposure protocol (Correct answer)

Correct answer: Squeeze the wound to express blood, flush with water, report to occupational health, and follow institutional exposure protocol

Post-exposure protocol includes immediate wound care (allow bleeding, flush with water/soap), reporting to employee health, and following the institution's bloodborne pathogen exposure plan, which may include prophylaxis.

Question 21: What is the function of Ia afferent fibers from muscle spindles?

Carry motor commands to intrafusal fibers
Signal dynamic and static muscle stretch to the spinal cord (Correct answer)
Detect Golgi tendon organ stretch
Signal nociception from muscle

Correct answer: Signal dynamic and static muscle stretch to the spinal cord

Ia afferents from primary endings of muscle spindles signal both the dynamic (velocity) and static (length) components of muscle stretch.

Question 22: Which wave in brainstem auditory evoked potentials (BAEPs) is thought to originate near the inferior colliculus and lateral lemniscus?

Wave III
Wave II
Wave I
Wave V (Correct answer)

Correct answer: Wave V

Wave V is the largest and most reliable BAEP component and is generated in the region of the lateral lemniscus and inferior colliculus in the midbrain.

Question 23: The popliteal fossa potential in tibial nerve SSEP recordings serves which primary purpose?

Verifying correct cortical electrode placement
Identifying the thalamic relay response
Measuring central conduction time
Confirming peripheral nerve activation proximal to the stimulation site (Correct answer)

Correct answer: Confirming peripheral nerve activation proximal to the stimulation site

The popliteal fossa electrode records the tibial nerve action potential as it passes behind the knee, confirming the peripheral pathway is intact before the spinal cord segment.

Question 24: In a patient with bilateral lower extremity amputations, evaluation of peripheral neuropathy EDX strategy should include:

Only H-reflexes at the knee level
No EDX is possible in amputees
Upper extremity NCS (median, ulnar, radial sensory and motor), sural at the stump if accessible, and EMG of residual limb muscles (Correct answer)
Upper extremity NCS only, which is sufficient to diagnose polyneuropathy

Correct answer: Upper extremity NCS (median, ulnar, radial sensory and motor), sural at the stump if accessible, and EMG of residual limb muscles

Upper extremity NCS can diagnose polyneuropathy and assess severity; if stump is accessible, residual nerve studies and EMG of residual limb muscles can provide additional information.

Question 25: Which parameter should be increased to eliminate stimulus artifact that is obscuring the onset of a short-latency sensory response?

Distance between the stimulating and recording electrodes (Correct answer)
Stimulation pulse duration
Amplifier gain
Low-frequency filter cutoff

Correct answer: Distance between the stimulating and recording electrodes

Increasing the distance between stimulator and recording electrodes allows the artifact to decay before the neural signal arrives, preventing overlap with the onset of the SNAP.

Question 26: What is the primary function of myelin in the nervous system?

Acts as a receptor
Connects neurons to muscles
Insulates axons and speeds signal conduction (Correct answer)
Produces neurotransmitters

Correct answer: Insulates axons and speeds signal conduction

Myelin is a fatty substance that forms a protective sheath around nerve fibers (axons). Its main function is to insulate the axon, preventing the dissipation of electrical signals and allowing nerve impulses to travel much faster along the axon through a process called saltatory conduction.

Question 27: What does the Erb's point potential represent in upper extremity SSEP recordings?

Thalamic relay response
Cervical spinal cord synaptic response
Brachial plexus activation recorded in the supraclavicular fossa (Correct answer)
Initial cortical arrival of the sensory volley

Correct answer: Brachial plexus activation recorded in the supraclavicular fossa

The Erb's point electrode is placed in the supraclavicular fossa and records the near-field potential generated by activation of the brachial plexus, confirming peripheral pathway integrity.

Question 28: What is the recommended minimum distance between a nerve stimulation site and an implanted deep brain stimulator (DBS) lead?

No minimum distance applies if current is under 10 mA
Stimulation ipsilateral to the DBS device is completely safe
At least 30 cm, and contralateral limbs only should be studied
At least 10 cm from any lead or pulse generator (Correct answer)

Correct answer: At least 10 cm from any lead or pulse generator

Current guidelines recommend keeping stimulation sites at least 10 cm from DBS leads and pulse generators to avoid device interaction or tissue heating.

Question 29: During needle EMG, a 'full interference pattern' at maximal effort indicates:

Myopathic process with early recruitment
Normal number of motor units firing rapidly and overlapping (Correct answer)
Severe neurogenic loss with few remaining units
Upper motor neuron disease

Correct answer: Normal number of motor units firing rapidly and overlapping

A full interference pattern means so many motor units are firing rapidly that individual MUPs can no longer be distinguished, which is normal at maximum voluntary contraction.

Question 30: When evaluating electrode impedance before beginning a study, which impedance value indicates adequately prepared skin for high-quality nerve conduction recordings?

Between 10–20 kΩ for optimal signal filtering
Impedance is irrelevant for surface electrode recordings
Above 50 kΩ indicates optimal electrode contact
Below 5 kΩ, with electrodes balanced within 1 kΩ of each other (Correct answer)

Correct answer: Below 5 kΩ, with electrodes balanced within 1 kΩ of each other

Inter-electrode impedance below 5 kΩ with balanced electrodes minimizes common-mode noise rejection errors and ensures high signal-to-noise ratio.

Question 31: For a single-fiber EMG (SFEMG) recording, which needle type and filter settings are required?

Monopolar needle with 20–2,000 Hz bandpass
Concentric needle with notch filter enabled
Concentric needle with 2–10,000 Hz bandpass
Single-fiber needle with high-pass filter of 500 Hz (Correct answer)

Correct answer: Single-fiber needle with high-pass filter of 500 Hz

SFEMG uses a specialized single-fiber needle electrode and a high-pass filter of 500 Hz to isolate action potentials from individual muscle fibers.

Question 32: A Martin-Gruber anastomosis (MGA) in the forearm causes which characteristic finding on routine nerve conduction studies?

Lower CMAP amplitude with ulnar proximal stimulation than distal stimulation
Higher CMAP amplitude with proximal median stimulation than with distal stimulation (Correct answer)
Prolonged median distal latency mimicking carpal tunnel syndrome
Absent F-wave with median wrist stimulation

Correct answer: Higher CMAP amplitude with proximal median stimulation than with distal stimulation

In MGA, median nerve fibers cross to the ulnar nerve in the forearm; stimulating the median nerve at the elbow produces a larger ulnar-muscle CMAP than wrist stimulation because the crossing fibers are activated proximally.

Question 33: What is the role of gamma motor neurons in muscle spindle function?

They set the sensitivity of the spindle by contracting intrafusal fibers (Correct answer)
They activate Golgi tendon organs during stretch
They relay signals from the spindle to the cerebellum
They inhibit Ia afferent discharge during contraction

Correct answer: They set the sensitivity of the spindle by contracting intrafusal fibers

Gamma motor neurons innervate intrafusal muscle fibers, adjusting spindle tension to maintain sensitivity across different muscle lengths during movement.

Question 34: What action ensures electrical safety during an EDX procedure?

Use extension cords
Disable safety checks
Use grounded equipment (Correct answer)
Skip impedance testing

Correct answer: Use grounded equipment

Using grounded equipment is a fundamental electrical safety measure during an EDX procedure. Grounding provides a safe path for stray electrical currents to dissipate, preventing electrical shocks to both the patient and the technician. This practice is crucial for minimizing electrical hazards and ensuring a secure testing environment.

Question 35: Infection control protocols in the EDX laboratory require that reusable needle electrodes:

Be stored in a dry container for 24 hours between uses
Be discarded only if visually contaminated
Be sterilized using approved sterilization methods or replaced with single-use disposable needles between patients (Correct answer)
Be wiped with alcohol between patients

Correct answer: Be sterilized using approved sterilization methods or replaced with single-use disposable needles between patients

Single-use disposable needles are the standard of care in most modern labs; if reusable needles are used, rigorous sterilization per facility policy is mandatory to prevent infection transmission.

Question 36: Satellite potentials seen on needle EMG are:

Independent discharges of denervated single fibers
Artifacts from nearby muscle activity
Normal findings in younger patients
Late components of MUPs linked to the main potential, indicating reinnervation (Correct answer)

Correct answer: Late components of MUPs linked to the main potential, indicating reinnervation

Satellite potentials are small late components time-locked to the main MUP, reflecting slow-conducting newly reinnervated muscle fibers linked to the same motor unit.

Question 37: A sensitivity setting of 20 µV/div would be most appropriate for recording which type of signal?

Compound muscle action potential (CMAP)
H-reflex response
Sensory nerve action potential (SNAP) (Correct answer)
F-wave response

Correct answer: Sensory nerve action potential (SNAP)

SNAPs are low-amplitude signals (typically 5–50 µV) that require higher sensitivity (smaller µV/div) compared to the millivolt-range CMAP.

Question 38: In evaluating a patient with suspected ALS, EMG evidence of active denervation must be found in how many body regions to meet El Escorial criteria?

3 regions (Correct answer)
2 regions
4 regions
1 region

Correct answer: 3 regions

Definite ALS by El Escorial criteria requires EMG evidence of lower motor neuron involvement (fibrillations, large MUPs, reduced recruitment) in at least 3 of 4 body regions.

Question 39: A patient discloses that they have a cochlear implant before undergoing NCS. What is the most important consideration?

Use only sensory NCS; motor NCS is absolutely contraindicated
The implant must be surgically removed before any NCS can be performed
Cochlear implants have no interaction with standard NCS equipment
Keep stimulation sites as far from the implant as possible and consult the manufacturer's guidelines (Correct answer)

Correct answer: Keep stimulation sites as far from the implant as possible and consult the manufacturer's guidelines

Electrical stimulation near a cochlear implant could potentially interfere with the device or its electrodes; manufacturer guidelines should be consulted and stimulation kept distant from the implant site.

Question 40: Neuromyotonia (Isaacs syndrome) is characterized on EMG by:

Regular fibrillation potentials at rest
Continuous high-frequency spontaneous MUP discharges that persist after nerve block (Correct answer)
Waxing and waning discharges that stop abruptly
Normal EMG with abnormal NCS

Correct answer: Continuous high-frequency spontaneous MUP discharges that persist after nerve block

Neuromyotonia shows continuous high-frequency spontaneous discharges that persist even after nerve block, indicating the abnormality is at the nerve terminal membrane level.

Question 41: What filter bandpass setting is typically recommended for somatosensory evoked potential (SSEP) recordings?

100–10,000 Hz
1–15 Hz
30–3000 Hz (Correct answer)
0.1–70 Hz

Correct answer: 30–3000 Hz

A bandpass of 30–3000 Hz is standard for SSEPs because it captures the brief, high-frequency transients of somatosensory responses while reducing low-frequency drift.

Question 42: Why must electrode impedance be checked before testing?

To improve display resolution
To equalize muscle tone
To increase signal noise
To ensure clear and accurate signal acquisition (Correct answer)

Correct answer: To ensure clear and accurate signal acquisition

Checking electrode impedance before testing is critical because high impedance can significantly degrade the quality of the acquired electrical signals. Poor contact or high resistance at the electrode-skin interface introduces noise and reduces the amplitude of the physiological signals, making them difficult to interpret. Ensuring low impedance guarantees clear, accurate, and reliable signal acquisition, which is essential for diagnostic accuracy.

Question 43: Which cranial nerve innervates the intrinsic muscles of the tongue?

CN IX (glossopharyngeal)
CN X (vagus)
CN V (trigeminal)
CN XII (hypoglossal) (Correct answer)

Correct answer: CN XII (hypoglossal)

The hypoglossal nerve (CN XII) provides motor innervation to all intrinsic and most extrinsic muscles of the tongue.

Question 44: Fasciculation potentials on needle EMG are most associated with which pathological process?

Neuromuscular junction dysfunction
Anterior horn cell disease such as ALS (Correct answer)
Acute myopathy
Sensory neuropathy

Correct answer: Anterior horn cell disease such as ALS

Fasciculations represent spontaneous discharge of entire motor units and are classically associated with lower motor neuron disease, especially anterior horn cell disorders like ALS.

Question 45: The end-plate potential (EPP) at the neuromuscular junction is generated by the influx of which ion?

K⁺ only
Na⁺ (and some Ca²⁺) through nicotinic ACh receptors (Correct answer)
Cl⁻
Ca²⁺ through L-type channels

Correct answer: Na⁺ (and some Ca²⁺) through nicotinic ACh receptors

Nicotinic acetylcholine receptors are nonselective cation channels; Na⁺ influx (along with minor Ca²⁺) generates the EPP that triggers muscle action potentials.

Question 46: The H-reflex is the electrophysiological analogue of which clinical reflex?

Ankle (Achilles) tendon reflex (Correct answer)
Hoffmann reflex
Patellar tendon reflex
Babinski reflex

Correct answer: Ankle (Achilles) tendon reflex

The H-reflex bypasses the muscle spindle and electrically activates Ia afferents, mimicking the ankle tendon (Achilles) reflex arc.

Question 47: Which setting determines the frequency range of detected signals?

Gain
Sweep speed
Filter (Correct answer)
Sensitivity

Correct answer: Filter

The filter setting on an EDX machine is crucial because it determines the specific frequency range of electrical signals that will be detected and displayed. By setting appropriate high-pass and low-pass filters, technicians can eliminate unwanted noise and artifacts while preserving the relevant physiological signals from nerves and muscles. This ensures a clear and interpretable waveform for accurate diagnosis.

Question 48: What is the function of the sweep speed setting?

Time axis adjustment (Correct answer)
Gain enhancer
Electrical resistance limiter
Volume control

Correct answer: Time axis adjustment

The sweep speed setting on an EDX machine controls the rate at which the waveform is displayed across the screen, essentially adjusting the time axis. A faster sweep speed compresses the waveform, showing more activity over a shorter period, while a slower sweep speed expands it, allowing for detailed examination of individual components. This adjustment is vital for visualizing the temporal characteristics of nerve and muscle potentials.

Question 49: When performing median motor nerve conduction studies, the active (G1) electrode is placed over which landmark?

Abductor pollicis brevis muscle belly (Correct answer)
Thenar eminence crease
First dorsal interosseous
Flexor pollicis longus

Correct answer: Abductor pollicis brevis muscle belly

The G1 electrode is placed over the belly of the abductor pollicis brevis (APB) to record the compound muscle action potential for median motor studies.

Question 50: In elderly patients, age-related changes in NCS include:

Reduced SNAP amplitudes, slightly slowed conduction velocities, and prolonged distal latencies (Correct answer)
Increased SNAP amplitudes and faster conduction velocities
Absent CMAP responses bilaterally
Markedly prolonged F-wave latencies with normal distal latencies

Correct answer: Reduced SNAP amplitudes, slightly slowed conduction velocities, and prolonged distal latencies

Normal aging causes gradual axonal loss and mild myelin changes, resulting in decreased SNAP amplitudes, mildly reduced conduction velocities, and slightly prolonged latencies.

Question 51: Which grounding principle is essential during nerve conduction studies to minimize electrical shock hazard to the patient?

The ground electrode must be placed distal to the recording electrode
Ground is optional when using modern digital amplifiers
The ground electrode must always be placed on the patient's chest
The ground electrode should be placed between the stimulating and recording electrodes (Correct answer)

Correct answer: The ground electrode should be placed between the stimulating and recording electrodes

Placing the ground electrode between the stimulator and recording electrodes reduces stimulus artifact and provides a common reference, improving both safety and signal quality.

Question 52: What click repetition rate is typically recommended for clinical BAEP recordings to balance efficiency with response quality?

50 clicks per second
10–11 clicks per second (Correct answer)
100 clicks per second
1 click per second

Correct answer: 10–11 clicks per second

A rate of approximately 10–11/s efficiently collects data while avoiding the significant amplitude reduction and latency prolongation seen at higher stimulation rates.

Question 53: When obtaining informed consent for an electrodiagnostic study, which element is legally and ethically required?

Patient must sign consent only for needle EMG, not for nerve conduction studies
Patient must be informed of the procedure, its purpose, risks, benefits, and alternatives (Correct answer)
Consent is only required for patients under 18 years of age
Verbal consent is never acceptable; only written consent is valid

Correct answer: Patient must be informed of the procedure, its purpose, risks, benefits, and alternatives

Valid informed consent requires disclosure of the procedure, its purpose, material risks (e.g., discomfort, bleeding, infection), benefits, and alternatives, allowing the patient to make an autonomous decision.

Question 54: What does a prolonged distal latency in a motor nerve conduction study primarily indicate?

Increased amplitude of the CMAP
Normal variation in conduction velocity
Slowed conduction at the distal segment, suggesting demyelination (Correct answer)
Axonal loss at the motor neuron

Correct answer: Slowed conduction at the distal segment, suggesting demyelination

Prolonged distal latency indicates slowed conduction in the distal nerve segment, which is characteristic of demyelinating pathology.

Question 55: The recommended stimulation rate for standard nerve conduction studies is:

1–3 Hz (Correct answer)
50 Hz
0.5–1 Hz
10–20 Hz

Correct answer: 1–3 Hz

Stimulation at 1–3 Hz allows sufficient recovery time between stimuli to prevent rate-dependent changes in CMAP or SNAP amplitude.

Question 56: Which EMG finding in paraspinal muscles supports a diagnosis of radiculopathy rather than plexopathy?

Large polyphasic MUPs in distal muscles
Absent H-reflex
Fibrillations and PSWs in paraspinal muscles at the affected level (Correct answer)
Fibrillations in limb muscles only

Correct answer: Fibrillations and PSWs in paraspinal muscles at the affected level

Paraspinal fibrillations at the appropriate spinal level support radiculopathy because the posterior primary ramus innervates paraspinal muscles proximal to the plexus.

Question 57: Why is supramaximal stimulation required for accurate nerve conduction studies?

To prevent patient discomfort
To ensure all axons in the nerve are activated, producing a maximal and reproducible evoked potential (Correct answer)
To achieve the fastest nerve conduction velocity
To test the strength of the stimulator

Correct answer: To ensure all axons in the nerve are activated, producing a maximal and reproducible evoked potential

Supramaximal stimulation (typically 20–30% above the level that produces maximal response) ensures all axons are activated, making amplitude and velocity measurements reliable.

Question 58: Needle gauge selection for EMG affects recordings because smaller gauge needles:

Record from a smaller territory, are less painful, but may have higher impedance (Correct answer)
Record from a larger territory and capture more motor units
Produce higher amplitude MUPs due to proximity
Are more durable and preferred for all studies

Correct answer: Record from a smaller territory, are less painful, but may have higher impedance

Smaller gauge needles have a smaller recording territory (reduced uptake area), causing less patient discomfort but potentially higher impedance and smaller recorded MUP amplitudes.

Question 59: A technician is setting up for a sural nerve SNAP and the signal appears noisy even after improving electrode contact. Which additional step is most appropriate?

Increase sweep speed to 50 ms/div
Reduce pulse duration to 0.05 ms
Use signal averaging to extract the low-amplitude SNAP from noise (Correct answer)
Switch to antidromic stimulation at a more distal site

Correct answer: Use signal averaging to extract the low-amplitude SNAP from noise

Signal averaging sums repeated responses, increasing the signal-to-noise ratio, which is especially useful for low-amplitude sensory potentials.

Question 60: Complex repetitive discharges (CRDs) on EMG are best described as:

Uniform repetitive discharges with abrupt onset and cessation, indicating chronic muscle denervation or myopathy (Correct answer)
Normal activity seen in healthy muscle at rest
High-amplitude potentials specific to ALS
Bursts of activity seen only during voluntary contraction

Correct answer: Uniform repetitive discharges with abrupt onset and cessation, indicating chronic muscle denervation or myopathy

CRDs are uniform repetitive discharges with machine-gun-like quality that start and stop abruptly; they indicate chronicity in either neurogenic or myopathic conditions.

Question 61: In diabetic polyneuropathy, the typical EDX pattern is:

Multifocal demyelinating neuropathy sparing sensory nerves
Length-dependent axonal sensorimotor polyneuropathy with earliest changes in distal lower extremity sensory nerves (Correct answer)
Focal conduction block at common compression sites only
Proximal motor neuropathy with normal sensory NCS

Correct answer: Length-dependent axonal sensorimotor polyneuropathy with earliest changes in distal lower extremity sensory nerves

Diabetic polyneuropathy is a length-dependent axonal process affecting the longest nerves first, so sural and peroneal responses are affected earliest.

Question 62: Which peroneal motor nerve conduction finding is most consistent with a fibular head compression neuropathy?

Prolonged distal latency only with no change across the fibular head
Focal slowing or conduction block between the ankle and below-fibular-head stimulation sites (Correct answer)
Symmetric slowing throughout the entire nerve
Absent CMAP at the ankle with normal above-fibular-head recording

Correct answer: Focal slowing or conduction block between the ankle and below-fibular-head stimulation sites

Focal slowing or amplitude drop specifically across the fibular head segment localizes the lesion to the site of compression at the fibular neck.

Question 63: EDX evaluation of a patient with bilateral carpal tunnel syndrome superimposed on diabetic polyneuropathy is challenging because:

Diabetic neuropathy may reduce baseline sensory amplitudes and slow conduction, making superimposed CTS difficult to isolate without comparison studies (Correct answer)
Diabetes accelerates NCS conduction velocities
Carpal tunnel syndrome does not occur with diabetes
Needle EMG is contraindicated in diabetics

Correct answer: Diabetic neuropathy may reduce baseline sensory amplitudes and slow conduction, making superimposed CTS difficult to isolate without comparison studies

Diabetic polyneuropathy reduces baseline SNAP amplitudes and mildly slows conduction; identifying additional focal slowing at the wrist (CTS) requires careful comparison of median versus ulnar responses.

Question 64: Absent sural sensory response with preserved peroneal motor response is consistent with:

Sciatic neuropathy distal to the short head of the biceps femoris (Correct answer)
L5 radiculopathy
Common peroneal neuropathy
Sacral plexopathy

Correct answer: Sciatic neuropathy distal to the short head of the biceps femoris

The sural nerve (sensory) and peroneal nerve (motor) share the sciatic nerve; absent sural with preserved peroneal suggests a lesion distal to where sural branches off, or affecting sural preferentially.

Question 65: During needle EMG, the technician notices visible muscle fasciculations at a needle insertion site in a patient with suspected ALS. What is the appropriate response?

Immediately withdraw the needle and terminate the study
Apply ice to reduce spontaneous activity before proceeding
Increase needle insertion depth to reach a deeper muscle layer
Document the finding, note the muscle, and continue with the planned examination (Correct answer)

Correct answer: Document the finding, note the muscle, and continue with the planned examination

Fasciculations are a clinically significant finding that should be documented in the specific muscle and reported; the examination should continue to gather complete diagnostic data.

Question 66: EDX findings in radial nerve palsy due to 'Saturday night palsy' (compression at the spiral groove) typically show:

Normal motor NCS to all radial-innervated muscles
Conduction block or axonal loss across the spiral groove sparing radial muscles proximal to the groove (Correct answer)
Absent median and ulnar sensory responses
Diffuse demyelinating polyneuropathy

Correct answer: Conduction block or axonal loss across the spiral groove sparing radial muscles proximal to the groove

Spiral groove compression spares proximal radial muscles (triceps, brachioradialis partially) while affecting wrist and finger extensors, with conduction block localized across the groove.

Question 67: What is the primary reason for using a concentric needle electrode rather than a monopolar needle in EMG recording?

Concentric needles deliver electrical stimulation simultaneously
Concentric needles record from a larger area of muscle tissue
Concentric needles allow deeper tissue penetration
Concentric needles are self-referencing, providing built-in differential recording with less noise (Correct answer)

Correct answer: Concentric needles are self-referencing, providing built-in differential recording with less noise

The concentric needle has its reference within the cannula, creating a differential recording pair that rejects common-mode noise without a separate surface reference.

Question 68: Which type of muscle fiber has the fastest contraction speed and is recruited last during voluntary effort?

Type I (slow-twitch)
Intrafusal fiber
Type IIa (fast-twitch oxidative)
Type IIx/IIb (fast-twitch glycolytic) (Correct answer)

Correct answer: Type IIx/IIb (fast-twitch glycolytic)

Type IIx/IIb fast-twitch glycolytic fibers contract fastest but fatigue quickly and are recruited only during high-force output per the size principle.

Question 69: Which stimulator parameter controls how long the electrical impulse is applied to the nerve during a nerve conduction study?

Pulse duration (µs) (Correct answer)
Frequency (Hz)
Sensitivity (mV/div)
Sweep speed (ms/div)

Correct answer: Pulse duration (µs)

Pulse duration (typically 0.1–0.2 ms for motor studies) determines the width of the stimulus waveform delivered to the nerve.

Question 70: In needle EMG, the term 'reduced recruitment' means:

Fewer motor units than expected are available to fire, reflecting motor unit loss (Correct answer)
Absence of all voluntary activity
Too many motor units firing for the level of force exerted
Motor units that fire irregularly

Correct answer: Fewer motor units than expected are available to fire, reflecting motor unit loss

Reduced recruitment indicates fewer functioning motor units than expected for a given level of voluntary effort, a hallmark of neurogenic disease.

Question 71: What technical error is most likely if a CMAP has an initial positive deflection before the main negative peak?

The high-frequency filter is set too low
The sweep speed is set too fast
The G1 electrode is placed over the tendon rather than the muscle belly (Correct answer)
The stimulation intensity is supramaximal

Correct answer: The G1 electrode is placed over the tendon rather than the muscle belly

An initial positive deflection (volume-conducted artifact) occurs when G1 is not placed over the end-plate zone or is off the muscle belly, causing the wavefront to travel toward rather than away from the electrode.

Question 72: Which part of the brain is responsible for coordinating movement and balance?

Medulla
Hypothalamus
Cerebellum (Correct answer)
Cerebrum

Correct answer: Cerebellum

The cerebellum, located at the back of the brain, is primarily responsible for coordinating voluntary movements, maintaining posture, balance, and motor learning. It integrates sensory input from the spinal cord with motor commands from the cerebral cortex to fine-tune movements.

Question 73: Which ion channel is primarily responsible for the rising phase of an action potential?

Voltage-gated potassium channels
Voltage-gated sodium channels (Correct answer)
Leak chloride channels
Ligand-gated calcium channels

Correct answer: Voltage-gated sodium channels

Voltage-gated sodium channels open rapidly in response to membrane depolarization, allowing Na⁺ influx that drives the rising phase of the action potential.

Question 74: Which finding on needle EMG is characteristic of acute denervation occurring within 1–3 weeks of injury?

Large polyphasic motor unit potentials
Fibrillation potentials and positive sharp waves (Correct answer)
Fasciculation potentials with normal MUPs
Reduced interference pattern only

Correct answer: Fibrillation potentials and positive sharp waves

Fibrillation potentials and positive sharp waves appear 1–3 weeks after axonal injury as denervated muscle fibers develop spontaneous instability of their resting membrane potential.

Question 75: For H-reflex recordings in adults, the active electrode is typically placed over which muscle?

Tibialis anterior
Abductor hallucis
Extensor digitorum brevis
Soleus (medial gastrocnemius) (Correct answer)

Correct answer: Soleus (medial gastrocnemius)

The H-reflex in adults is most reliably recorded from the soleus/medial gastrocnemius via tibial nerve stimulation at the popliteal fossa.

Question 76: The fasciculus gracilis in the dorsal columns carries sensory information from which body region?

Visceral afferents from the thorax
Face and scalp
Lower limbs and trunk below T6 (Correct answer)
Upper limbs and trunk above T6

Correct answer: Lower limbs and trunk below T6

The fasciculus gracilis, located medially in the dorsal columns, carries proprioception, vibration, and fine touch from the lower extremities and trunk below T6.

Question 77: The recruitment pattern in a myopathic process typically shows:

Reduced recruitment with large MUPs
Early recruitment with small, short-duration MUPs (Correct answer)
Discrete pattern at maximal effort
Absent voluntary activity

Correct answer: Early recruitment with small, short-duration MUPs

Myopathies reduce the force-generating capacity of individual muscle fibers, requiring more motor units to fire early to compensate, producing early recruitment of small MUPs.

Question 78: Why is obtaining informed consent essential before an electrodiagnostic study?

To explain the procedure and obtain permission (Correct answer)
To begin testing immediately
To determine insurance eligibility
To reduce paperwork

Correct answer: To explain the procedure and obtain permission

Obtaining informed consent is an essential ethical and legal requirement before any medical procedure, including an electrodiagnostic study. It ensures that the patient fully understands the nature of the test, its purpose, potential risks, benefits, and alternatives. This process empowers the patient to make an autonomous decision and grants the healthcare provider permission to proceed with the study.

Question 79: During an upper extremity sensory nerve conduction study, antidromic technique means:

Stimulating and recording at the same site simultaneously
Stimulating proximally and recording distally in the direction opposite to normal sensory conduction (Correct answer)
Stimulating distally and recording proximally in the normal direction of sensory conduction
Using a needle electrode for both stimulation and recording

Correct answer: Stimulating proximally and recording distally in the direction opposite to normal sensory conduction

Antidromic stimulation sends the impulse against the normal direction of sensory conduction (proximal stimulus, distal recording), which typically yields larger amplitudes but may pick up volume-conducted motor responses.

Question 80: Chronic inflammatory demyelinating polyneuropathy (CIDP) is differentiated from Charcot-Marie-Tooth (CMT) type 1 on EDX by:

Normal SNAP amplitudes in CMT
Acquired features in CIDP: conduction block, temporal dispersion, and asymmetric slowing versus uniform slowing in CMT (Correct answer)
Absent F-waves in CMT only
Presence of slowed conduction velocity in CIDP only

Correct answer: Acquired features in CIDP: conduction block, temporal dispersion, and asymmetric slowing versus uniform slowing in CMT

CIDP shows acquired, often asymmetric demyelination with conduction block and temporal dispersion, while CMT1 shows uniform, symmetric slowing without conduction block.

Question 81: Which infection control practice is specifically required when performing needle EMG on an immunocompromised patient (e.g., post-chemotherapy)?

Avoidance of all paraspinal muscles only
Strict sterile technique including sterile gloves and an antiseptic skin wipe at each insertion site (Correct answer)
Postpone the study until the patient's white cell count normalizes
Use of thicker-gauge needles to reduce procedural time

Correct answer: Strict sterile technique including sterile gloves and an antiseptic skin wipe at each insertion site

Immunocompromised patients face heightened infection risk from needle insertion; antiseptic skin preparation and sterile gloves at each site minimize the risk of introducing skin flora into deeper tissues.

Question 82: The dorsal root ganglion (DRG) contains the cell bodies of which neuron type?

Autonomic preganglionic neurons
Primary sensory afferent neurons (Correct answer)
Lower motor neurons
Upper motor neurons

Correct answer: Primary sensory afferent neurons

The DRG houses the cell bodies of primary sensory (afferent) neurons that transmit sensory signals from the periphery to the spinal cord.

Question 83: EDX evaluation of multifocal motor neuropathy (MMN) characteristically reveals:

Symmetric axonal polyneuropathy with sensory predominance
Normal NCS with myopathic EMG
Multiple sites of persistent motor conduction block without sensory abnormalities (Correct answer)
Diffuse demyelination with sensory involvement

Correct answer: Multiple sites of persistent motor conduction block without sensory abnormalities

MMN is characterized by multiple sites of persistent motor conduction block (>50% amplitude drop) with normal sensory NCS, distinguishing it from CIDP.

Question 84: In ulnar neuropathy at the elbow, the most diagnostic NCS finding is:

Focal slowing of ulnar motor conduction velocity across the elbow segment (Correct answer)
Absent ulnar sensory response at the wrist
Reduced radial sensory amplitude
Prolonged median distal motor latency

Correct answer: Focal slowing of ulnar motor conduction velocity across the elbow segment

Focal slowing of ulnar motor conduction velocity across the elbow segment localizes the lesion to the cubital tunnel or elbow region.

Question 85: Myotonic discharges on needle EMG are characterized by:

Waxing and waning frequency and amplitude producing a dive-bomber sound (Correct answer)
Constant frequency and amplitude
Decremental response to repetitive nerve stimulation
Single high-amplitude bursts at rest

Correct answer: Waxing and waning frequency and amplitude producing a dive-bomber sound

Myotonic discharges wax and wane in both frequency and amplitude, producing the classic 'dive-bomber' or revving motorcycle sound on the EMG speaker.

Question 86: During a somatosensory evoked potential (SSEP) study, the patient must remain still for extended periods. Which safety consideration is unique to SSEP compared to routine EMG/NCS?

SSEP cannot be performed on patients with a history of seizures
SSEP stimulation is contraindicated in patients with peripheral neuropathy
SSEP requires higher stimulation current, increasing burn risk at the electrode site
Prolonged immobility raises pressure injury risk, especially over bony prominences (Correct answer)

Correct answer: Prolonged immobility raises pressure injury risk, especially over bony prominences

SSEP studies can require the patient to lie still for 30–60 minutes; pressure redistribution and padding of bony prominences are necessary to prevent skin breakdown, particularly in patients with sensory deficits.

Question 87: During a nerve conduction study, increasing the stimulus intensity beyond the supramaximal level will have what effect on the CMAP amplitude?

Amplitude continues to increase proportionally
Amplitude decreases due to co-stimulation of inhibitory fibers
Amplitude remains stable (plateau) because all fibers are already activated (Correct answer)
Amplitude fluctuates unpredictably

Correct answer: Amplitude remains stable (plateau) because all fibers are already activated

Once all axons are depolarized at supramaximal stimulation, additional intensity cannot recruit more fibers, so amplitude plateaus.

Question 88: What is the standard interelectrode distance recommended for recording the median motor CMAP from the abductor pollicis brevis (APB)?

8 cm
1 cm
3 cm (Correct answer)
Distance is not standardized for this study

Correct answer: 3 cm

The active electrode is placed over the APB muscle belly and the reference electrode approximately 3–4 cm distally at the proximal thumb IP joint, ensuring consistent and reproducible recordings.

Question 89: A technician notices 60 Hz artifact on the EMG display. Which step should be taken FIRST?

Check and improve electrode impedance and ground connections (Correct answer)
Increase the sensitivity setting
Enable the notch filter immediately
Reduce the sweep speed

Correct answer: Check and improve electrode impedance and ground connections

Poor electrode contact and inadequate grounding are the most common causes of 60 Hz artifact, and correcting these is preferred before using the notch filter.

Question 90: An EDX laboratory quality assurance program should include:

Establishing normal reference values for the lab's specific patient population, equipment, and technique (Correct answer)
Using only published reference values without local validation
Testing only new equipment annually
Performing NCS on a single normal subject yearly

Correct answer: Establishing normal reference values for the lab's specific patient population, equipment, and technique

Each EDX lab should establish its own normal values because reference ranges vary with patient demographics, equipment type, electrode placement techniques, and lab temperature protocols.

Question 91: Why is calibration of EDX equipment important?

Minimizes electrode use
Ensures diagnostic accuracy (Correct answer)
Creates colorful displays
Enhances audio output

Correct answer: Ensures diagnostic accuracy

Calibration of electrodiagnostic (EDX) equipment is a fundamental procedure that ensures the accuracy and reliability of the measurements. Regular calibration verifies that the machine is producing precise and consistent readings, which is essential for making correct diagnostic interpretations. Without proper calibration, results could be misleading, potentially leading to incorrect diagnoses or treatment plans.

Question 92: Which of the following best describes the correct documentation requirement after completing an electrodiagnostic study?

Documentation can be deferred until the final report is issued by the interpreting physician
All waveforms, measurements, patient positioning, limb temperatures, and technical parameters must be recorded (Correct answer)
Only abnormal findings need to be documented in the patient record
Only the interpreting physician is responsible for documenting technical parameters

Correct answer: All waveforms, measurements, patient positioning, limb temperatures, and technical parameters must be recorded

Comprehensive documentation of all technical parameters—waveforms, latencies, amplitudes, temperatures, electrode positions—is required for medicolegal accountability and ensures reproducible future studies.

Question 93: Which spinal cord levels form the lumbosacral plexus roots that contribute to the sciatic nerve?

L4–S3 (Correct answer)
C5–C8 and T1
L1–L3
S2–S4

Correct answer: L4–S3

The sciatic nerve is formed from anterior rami of L4 through S3, making it the largest nerve in the body.

Question 94: A needle EMG finding of increased polyphasia (>20% polyphasic MUPs) in a muscle indicates:

Definitive diagnosis of ALS
Possible pathology suggesting reinnervation or myopathy causing desynchronized fiber firing (Correct answer)
Normal voluntary activity in trained athletes
Isolated peripheral nerve injury

Correct answer: Possible pathology suggesting reinnervation or myopathy causing desynchronized fiber firing

Increased polyphasia reflects desynchronized firing of muscle fibers within a motor unit, seen in both neurogenic (reinnervation) and myopathic conditions.

Question 95: What is the purpose of checking electrical isolation of EDX equipment before performing studies on a patient connected to other medical devices (e.g., IV pump, cardiac monitor)?

To prevent stray leakage currents from flowing through the patient between devices, causing microshock (Correct answer)
To verify that the IV pump will not introduce 60 Hz artifact into the EMG signal
To confirm the EDX machine is properly grounded to building electrical ground
To ensure the EDX amplifier does not interfere with the cardiac monitor display

Correct answer: To prevent stray leakage currents from flowing through the patient between devices, causing microshock

When multiple devices are connected to a patient, leakage currents can sum and reach levels capable of causing ventricular fibrillation (microshock), particularly in patients with intracardiac catheters.

Question 96: In the EMG report, the section describing the clinical indication and relevant history is important because:

It replaces the need for objective numerical data
It provides context that is essential for accurately interpreting the EDX findings in relation to the clinical question (Correct answer)
It is only necessary for academic publications
It is required for billing purposes only

Correct answer: It provides context that is essential for accurately interpreting the EDX findings in relation to the clinical question

Clinical context allows the interpreting physician to correlate EDX abnormalities with the clinical presentation, ensuring findings are interpreted in the appropriate clinical framework.

Question 97: The primary purpose of the reference electrode in a monopolar needle EMG recording is:

To stimulate the nerve at a distant site
To deliver the return path for the stimulator current
To provide an electrically neutral reference point so the differential amplifier records only local muscle activity (Correct answer)
To measure skin temperature continuously

Correct answer: To provide an electrically neutral reference point so the differential amplifier records only local muscle activity

The reference electrode provides a neutral potential for the differential amplifier; the active needle minus the reference captures local muscle electrical activity while rejecting common-mode noise.

Question 98: Which needle EMG finding is most characteristic of a myopathic process?

Fasciculations with giant MUPs
Early full recruitment of small, short-duration, polyphasic MUPs (Correct answer)
Reduced recruitment of large, long-duration MUPs
Abundant fibrillation potentials with normal MUP morphology

Correct answer: Early full recruitment of small, short-duration, polyphasic MUPs

Myopathy produces small, short-duration, polyphasic MUPs that recruit early (at low force levels) because individual motor units generate less force due to fiber loss within each unit.

Question 99: Which of the following represents the correct procedure if a needle electrode accidentally contacts bone during EMG?

Continue recording, as bone contact does not affect the needle tip
Apply more insertion force to pass through the periosteum
Discard the needle immediately and use a new one, as the tip may be bent or burred (Correct answer)
Withdraw the needle slightly, reposition, and continue recording

Correct answer: Discard the needle immediately and use a new one, as the tip may be bent or burred

Contact with bone can blunt or deform the needle tip, increasing insertion pain and tissue trauma; a new needle should be used to maintain patient safety and signal quality.

Question 100: What is a critical infection control step before patient contact?

Wearing a name badge
Performing hand hygiene (Correct answer)
Turning off lights
Adjusting the monitor

Correct answer: Performing hand hygiene

Performing hand hygiene, such as washing hands with soap and water or using an alcohol-based hand rub, is the single most critical infection control step before any patient contact. This practice significantly reduces the transmission of microorganisms, protecting both the patient from healthcare-associated infections and the healthcare worker from potential pathogens. It is a cornerstone of patient safety.

Question 101: Which of the following is a common technical artifact that can falsely prolong distal latency in motor NCS?

Increasing stimulus duration
Using a low-impedance ground electrode
High filter settings
Recording electrode placement over the tendon rather than the muscle belly (Correct answer)

Correct answer: Recording electrode placement over the tendon rather than the muscle belly

Placing the active electrode over the tendon instead of the muscle belly produces a volume-conducted response with apparent latency prolongation and altered waveform morphology.

Question 102: In a patient with polyneuropathy, which pattern of NCS abnormalities suggests primary demyelination?

Absent F-waves with normal distal latencies
Symmetric reduction in CMAP and SNAP amplitudes
Uniform slowing of conduction velocities with prolonged distal latencies (Correct answer)
Asymmetric amplitude reductions with normal velocities

Correct answer: Uniform slowing of conduction velocities with prolonged distal latencies

Primary demyelinating polyneuropathy shows uniform slowing of conduction velocities and prolonged distal latencies, reflecting widespread myelin damage.

Question 103: What is the primary purpose of applying a ground electrode during nerve conduction studies?

Increase the amplitude of the recorded potential
Prevent patient burns at the stimulation site
Shorten the distal latency measurement
Reduce common-mode electrical noise and improve signal quality (Correct answer)

Correct answer: Reduce common-mode electrical noise and improve signal quality

The ground electrode provides a reference point that helps the differential amplifier cancel out common-mode interference, reducing electrical noise in the recording.

Question 104: When the cathode and anode of the stimulating electrode are accidentally reversed during a nerve conduction study, what is the most notable effect?

The stimulator output automatically compensates with no effect
The sweep is triggered but no potential is recorded
Anodal stimulation creates virtual cathode depolarization at a more proximal site, artificially shortening latency (Correct answer)
The CMAP amplitude doubles due to anodal blocking

Correct answer: Anodal stimulation creates virtual cathode depolarization at a more proximal site, artificially shortening latency

When the anode is inadvertently placed distally, hyperpolarization under the anode can cause virtual cathode effects that activate the nerve at a site closer to the recording electrode, falsely shortening the measured latency.

Question 105: The P37 component in lower extremity tibial nerve SSEPs is generated by which anatomical structure?

Lumbar spinal cord dorsal horn
Popliteal fossa nerve trunk
Paracentral lobule of the contralateral primary somatosensory cortex (Correct answer)
Thalamus

Correct answer: Paracentral lobule of the contralateral primary somatosensory cortex

P37 is the cortical response to tibial nerve stimulation generated in the paracentral lobule, which is the medial cortical representation for lower extremity sensation.

Question 106: For EDX evaluation of a patient with obesity (BMI >40), a key technical adjustment is:

Avoiding all sensory nerve studies
Increasing stimulus intensity and potentially needle electrode placement for NCS to achieve supramaximal stimulation through thick tissue (Correct answer)
Using only bipolar surface electrodes for EMG
Decreasing stimulus intensity to prevent discomfort

Correct answer: Increasing stimulus intensity and potentially needle electrode placement for NCS to achieve supramaximal stimulation through thick tissue

Increased subcutaneous fat in obese patients attenuates electrical stimulation; higher intensities are needed to depolarize deep nerves, and near-nerve needle stimulation may be necessary.

Question 107: In evaluating a patient with chemotherapy-induced peripheral neuropathy (CIPN), EDX typically shows:

Multifocal motor neuropathy
Normal NCS with myopathic EMG
Length-dependent axonal sensory-predominant polyneuropathy affecting distal SNAP amplitudes earliest (Correct answer)
Proximal demyelinating polyneuropathy

Correct answer: Length-dependent axonal sensory-predominant polyneuropathy affecting distal SNAP amplitudes earliest

Most chemotherapy agents (taxanes, platinum compounds, vinca alkaloids) cause length-dependent axonal sensory-predominant neuropathy, with sural SNAP amplitude reduction being an early and sensitive finding.

Question 108: When performing needle EMG of the first dorsal interosseous (FDI), the main clinical purpose is to evaluate:

Median nerve at the wrist
Ulnar nerve and/or C8/T1 roots (Correct answer)
Radial nerve in the forearm
C6 nerve root

Correct answer: Ulnar nerve and/or C8/T1 roots

The FDI is innervated by the ulnar nerve (deep branch) and reflects C8/T1 myotomal innervation, making it useful for evaluating ulnar nerve or C8/T1 pathology.

Question 109: The insertional activity on needle EMG is normally:

Absent in all muscles
Prolonged trains of fibrillations lasting >1 second
A brief burst of electrical activity lasting only as long as needle movement (Correct answer)
Large polyphasic potentials at rest

Correct answer: A brief burst of electrical activity lasting only as long as needle movement

Normal insertional activity is a brief burst of electrical potentials generated by mechanical irritation of muscle fibers that stops immediately when needle movement ceases.

Question 110: In axonal neuropathy affecting the sural nerve, which NCS finding is expected?

Reduced conduction velocity with normal SNAP amplitude
Prolonged distal latency with normal amplitude
Normal latency with reduced SNAP amplitude (Correct answer)
Normal sural NCS in all axonal neuropathies

Correct answer: Normal latency with reduced SNAP amplitude

Axonal loss reduces the number of conducting fibers, lowering SNAP amplitude while conduction velocity (determined by surviving myelinated fibers) remains relatively preserved.

Question 111: In evaluating hereditary neuropathy with liability to pressure palsies (HNPP), EDX characteristically shows:

Pure axonal polyneuropathy
Mild baseline slowing with markedly prolonged latencies and conduction block at typical compression sites (Correct answer)
Normal NCS with myopathic EMG
Diffuse uniform slowing consistent with CMT type 1

Correct answer: Mild baseline slowing with markedly prolonged latencies and conduction block at typical compression sites

HNPP shows mild background slowing with exaggerated, disproportionate slowing and conduction block at typical entrapment sites (carpal tunnel, fibular head, cubital tunnel).

Question 112: The N13 component recorded over the posterior cervical spine in upper extremity SSEPs is generated at which anatomical level?

Primary somatosensory cortex
Thalamus
Cervical spinal cord and dorsal column nuclei at the cervicomedullary junction (Correct answer)
Brachial plexus

Correct answer: Cervical spinal cord and dorsal column nuclei at the cervicomedullary junction

N13 reflects postsynaptic activity in the cervical dorsal horn and dorsal column nuclei, and is used to differentiate cervical cord lesions from more rostral pathology.

Question 113: What anatomical structure separates the brachial plexus into divisions above and below it?

First rib
Coracoid process
Scalene muscles
Clavicle (Correct answer)

Correct answer: Clavicle

The clavicle divides the brachial plexus into supraclavicular (trunks) and infraclavicular (cords) segments.

Question 114: A prolonged minimum F-wave latency with normal distal motor latency and conduction velocity suggests:

Myopathy
Distal axonal neuropathy
Proximal nerve or nerve root conduction slowing (Correct answer)
Neuromuscular junction disorder

Correct answer: Proximal nerve or nerve root conduction slowing

Prolonged minimum F-wave latency with normal distal parameters indicates abnormal conduction in the proximal nerve or root segment.

Question 115: When testing for carpal tunnel syndrome, which additional nerve conduction technique provides increased diagnostic sensitivity compared to routine median studies alone?

Median-to-ulnar comparative sensory studies (palm stimulation) (Correct answer)
Blink reflex testing
Median motor conduction to flexor pollicis longus
Median F-wave latency measurement

Correct answer: Median-to-ulnar comparative sensory studies (palm stimulation)

Comparative palm stimulation studies (median vs. ulnar) across the carpal tunnel are among the most sensitive techniques for detecting mild median neuropathy at the wrist.

Question 116: 60 Hz power line interference on the EMG tracing is best eliminated by:

Optimizing skin preparation, reducing electrode impedance, and ensuring proper grounding (Correct answer)
Increasing sweep speed to compress the signal
Decreasing amplifier gain
Increasing stimulus intensity

Correct answer: Optimizing skin preparation, reducing electrode impedance, and ensuring proper grounding

60 Hz interference is primarily caused by high electrode impedance; good skin preparation (abrasion and cleaning) and proper ground electrode placement reduce this artifact.

Question 117: The F-wave latency is used clinically to evaluate which segment of the peripheral nervous system?

Distal nerve terminals
Proximal nerve and nerve root segments (Correct answer)
Sensory dorsal root ganglion
Neuromuscular junction

Correct answer: Proximal nerve and nerve root segments

F-waves travel antidromically to the anterior horn cell and back, making their latency sensitive to conduction abnormalities in proximal nerve segments and nerve roots.

Question 118: To minimize the risk of infection transmission in the EDX laboratory, which practice is correct regarding surface electrode reuse?

Wipe surface electrodes with a dry cloth between patients
Surface electrodes never require disinfection as they contact only intact skin
Soak surface electrodes in saline for 10 minutes between uses
Disinfect reusable surface electrodes with an EPA-approved disinfectant between patients (Correct answer)

Correct answer: Disinfect reusable surface electrodes with an EPA-approved disinfectant between patients

Reusable surface electrodes must be cleaned with an EPA-registered disinfectant between patients to reduce transmission of microorganisms, including MRSA.

Question 119: In a patient with end-stage renal disease on hemodialysis, expected EDX findings include:

Pure demyelinating neuropathy
Length-dependent axonal sensorimotor polyneuropathy (uremic neuropathy) (Correct answer)
Normal EDX in all patients on dialysis
Focal entrapment neuropathies only

Correct answer: Length-dependent axonal sensorimotor polyneuropathy (uremic neuropathy)

Uremic neuropathy is a length-dependent axonal sensorimotor polyneuropathy caused by accumulation of uremic toxins, with distal sensory nerves affected earliest.

Question 120: Positive sharp waves (PSWs) on EMG are considered abnormal when:

They persist beyond needle movement and occur spontaneously at rest (Correct answer)
They are seen only in paraspinal muscles
They appear during voluntary contraction
They occur only with needle insertion

Correct answer: They persist beyond needle movement and occur spontaneously at rest

PSWs are abnormal when they occur spontaneously at rest beyond the area of needle insertion, indicating denervation or muscle membrane instability.

Question 121: Wartenberg syndrome (superficial radial nerve entrapment) is confirmed on EDX by:

Absent median motor response
Prolonged radial motor distal latency
Absent ulnar sensory response
Reduced or absent superficial radial sensory SNAP (Correct answer)

Correct answer: Reduced or absent superficial radial sensory SNAP

Wartenberg syndrome involves compression of the superficial radial sensory nerve at the forearm; EDX confirmation requires reduced or absent superficial radial SNAP.

Question 122: What does 'P100' refer to in visual evoked potential (VEP) recordings?

A positive polarity peak occurring approximately 100 ms after the visual stimulus (Correct answer)
A positive peak with amplitude of 100 µV
A negative peak occurring 100 ms before stimulus onset
The 100th averaged response waveform

Correct answer: A positive polarity peak occurring approximately 100 ms after the visual stimulus

P100 is a positive-polarity component peaking around 100 ms post-stimulus and is the primary waveform evaluated in clinical VEP studies.

Question 123: When setting up for a blink reflex study, where should the active (E1) recording electrode be placed?

Over the frontalis muscle
At the lateral canthus of the eye
Over the masseter muscle
Below the eye, over the orbicularis oculi muscle (Correct answer)

Correct answer: Below the eye, over the orbicularis oculi muscle

The orbicularis oculi is the target muscle for blink reflex recordings; E1 is placed infraorbitally beneath the eye.

Question 124: A sural sensory study is most useful for evaluating which clinical condition?

Median neuropathy at the wrist
Length-dependent peripheral neuropathy (Correct answer)
Cervical radiculopathy at C6
Brachial plexopathy involving the upper trunk

Correct answer: Length-dependent peripheral neuropathy

The sural nerve is a pure sensory nerve in the distal leg and is highly sensitive to length-dependent (dying-back) axonal neuropathies that affect distal nerves first.

Question 125: A compound muscle action potential (CMAP) with normal distal latency but reduced amplitude most likely indicates:

Neuromuscular junction disorder
Axonal motor neuropathy (Correct answer)
Central nervous system lesion
Demyelinating neuropathy

Correct answer: Axonal motor neuropathy

Reduced CMAP amplitude with normal distal latency is the hallmark of axonal motor neuropathy, reflecting loss of motor axons.

Question 126: Why is limb temperature monitoring critical before performing nerve conduction studies?

Cold temperatures increase nerve conduction velocity, leading to false-positive results
Temperature monitoring is only required for pediatric patients
Low limb temperature slows conduction velocity and prolongs distal latencies, mimicking neuropathy (Correct answer)
Temperature affects only sensory amplitudes, not motor latencies

Correct answer: Low limb temperature slows conduction velocity and prolongs distal latencies, mimicking neuropathy

Conduction velocity decreases approximately 1.5–2.4 m/s per degree Celsius of cooling, so cold limbs can produce falsely prolonged latencies consistent with neuropathy.

Question 127: Fasciculation potentials differ from fibrillation potentials in that fasciculations:

Are always pathological
Represent spontaneous discharge of an entire motor unit (Correct answer)
Are smaller in amplitude and shorter in duration
Occur only in denervated muscle fibers

Correct answer: Represent spontaneous discharge of an entire motor unit

Fasciculation potentials represent the spontaneous, involuntary discharge of an entire motor unit, appearing as complex polyphasic potentials of larger amplitude.

Question 128: When EDX shows absent bilateral peroneal and tibial motor responses with intact sural sensory responses, the most likely diagnosis is:

Motor neuron disease or severe motor neuropathy (Correct answer)
Sensory polyneuropathy
Brachial plexopathy
Myopathy

Correct answer: Motor neuron disease or severe motor neuropathy

Absent motor responses with preserved sensory responses suggest a motor predominant process, consistent with motor neuron disease or a motor neuropathy like multifocal motor neuropathy.

Question 129: Which electrode configuration is used for the active (E1) recording electrode in a standard nerve conduction study?

Placed at a fixed distance of 10 cm from the cathode
Placed over the motor point or muscle belly (Correct answer)
Placed proximal to the reference electrode
Placed over bone to reduce muscle artifact

Correct answer: Placed over the motor point or muscle belly

E1 is placed over the motor point (belly) of the target muscle to maximize CMAP amplitude.

Question 130: The superficial peroneal nerve provides sensory innervation to which skin region?

Sole of the foot
Web space between the first and second toes
Dorsum of the foot (except the first web space) (Correct answer)
Lateral heel

Correct answer: Dorsum of the foot (except the first web space)

The superficial peroneal nerve supplies cutaneous sensation to most of the dorsum of the foot, while the deep peroneal covers only the first web space.

Question 131: EDX evaluation of a meralgia paresthetica (lateral femoral cutaneous nerve entrapment) relies primarily on:

Lateral femoral cutaneous nerve sensory NCS comparing symptomatic to asymptomatic side (Correct answer)
EMG of quadriceps muscle
Femoral motor nerve conduction study
H-reflex from the quadriceps

Correct answer: Lateral femoral cutaneous nerve sensory NCS comparing symptomatic to asymptomatic side

The lateral femoral cutaneous nerve is a pure sensory nerve; LFCN sensory NCS comparing sides (amplitude and latency) is the primary EDX test for meralgia paresthetica.

Question 132: Why should a technician verify the patient's identity before testing?

To assign equipment
To record demographics
To ensure accurate patient matching (Correct answer)
To avoid asking for ID again

Correct answer: To ensure accurate patient matching

Verifying the patient's identity before testing is a critical safety protocol to ensure that the correct procedure is performed on the correct individual. This step prevents medical errors, such as performing the wrong test or misattributing results, which could have serious consequences for patient care. Accurate patient matching is fundamental to safe and effective healthcare delivery.

Question 133: Which of the following best describes the role of the differential amplifier in electrodiagnostic equipment?

It converts analog signals to digital without amplification
It amplifies only the signal at E1 while ignoring E2
It amplifies the difference between E1 and E2, rejecting signals common to both (Correct answer)
It filters high-frequency noise above 10 kHz

Correct answer: It amplifies the difference between E1 and E2, rejecting signals common to both

A differential amplifier subtracts the E2 signal from E1, amplifying the desired potential while rejecting common-mode interference.

Question 134: In a pregnant patient with suspected carpal tunnel syndrome, EDX evaluation is considered:

Absolutely contraindicated due to electrical current risk to the fetus
Safe only in the first trimester
Generally safe with standard precautions, as NCS and EMG currents are localized to the extremity and do not reach the fetus (Correct answer)
Requires general anesthesia

Correct answer: Generally safe with standard precautions, as NCS and EMG currents are localized to the extremity and do not reach the fetus

Standard EDX studies in pregnant patients are considered safe because the stimulus currents are localized to the extremity and the very small currents used in NCS/EMG do not travel to the uterus.

Question 135: What is the minimum recommended limb temperature for performing accurate upper extremity nerve conduction studies?

30°C
28°C
36°C
32°C (Correct answer)

Correct answer: 32°C

Upper extremity skin temperature should be at least 32°C to avoid cold-induced slowing that can falsely mimic neuropathy; the lower extremity standard is 30–31°C.

Question 136: Which division of the nervous system controls involuntary body functions?

Somatic nervous system
Central nervous system
Peripheral sensory nerves
Autonomic nervous system (Correct answer)

Correct answer: Autonomic nervous system

The autonomic nervous system (ANS) is a division of the peripheral nervous system that controls involuntary bodily functions such as heart rate, digestion, respiration, and blood pressure. It operates without conscious thought, regulating internal organs and glands to maintain homeostasis.

Question 137: The absolute refractory period of a nerve fiber corresponds to which channel state?

Na⁺ channels are in the inactivated (closed) state (Correct answer)
K⁺ channels are maximally closed
All Na⁺ channels are open
The membrane is at its resting potential

Correct answer: Na⁺ channels are in the inactivated (closed) state

During the absolute refractory period, voltage-gated Na⁺ channels are inactivated and cannot reopen regardless of stimulus strength, preventing a new action potential.

Question 138: Temporal dispersion in a motor nerve conduction study refers to:

Broadening and reduction of CMAP with proximal stimulation (Correct answer)
Increased CMAP amplitude with repetitive stimulation
Increased conduction velocity across a segment
Absent F-waves bilaterally

Correct answer: Broadening and reduction of CMAP with proximal stimulation

Temporal dispersion refers to the broadening and amplitude reduction of the CMAP with proximal stimulation, caused by differential slowing of demyelinated axons.

Question 139: EDX findings in polymyositis or dermatomyositis (inflammatory myopathy) typically include:

Normal EMG with reduced CMAP amplitudes
Discrete recruitment pattern on maximal effort
Fibrillations, PSWs, myotonic discharges, and small short-duration polyphasic MUPs with early recruitment (Correct answer)
Large polyphasic MUPs with reduced recruitment

Correct answer: Fibrillations, PSWs, myotonic discharges, and small short-duration polyphasic MUPs with early recruitment

Inflammatory myopathies show active denervation potentials (fibrillations, PSWs) reflecting muscle fiber membrane irritability, plus small short-duration polyphasic MUPs with early recruitment.

Question 140: An H-reflex is most reliably elicited in adults by stimulating which nerve?

Femoral nerve at the groin
Peroneal nerve at the fibular head
Sural nerve at the ankle
Tibial nerve at the popliteal fossa (Correct answer)

Correct answer: Tibial nerve at the popliteal fossa

The H-reflex is most consistently recorded from the soleus/gastrocnemius by stimulating the tibial nerve in the popliteal fossa with long-duration, low-intensity stimuli.

Question 141: The anterior horn of the spinal cord gray matter primarily contains cell bodies of which neurons?

Postganglionic sympathetic neurons
Interneurons only
Sensory neurons
Lower motor neurons (alpha motor neurons) (Correct answer)

Correct answer: Lower motor neurons (alpha motor neurons)

Alpha motor neurons located in the anterior horn innervate skeletal muscle fibers and are the final common pathway for voluntary movement.

Question 142: A technician performing median nerve sensory NCS obtains a SNAP with a normal onset latency but significantly reduced amplitude. Before concluding pathology, which technical factor should be reviewed first?

Notch filter status
Sweep speed setting
E1 electrode placement accuracy over the nerve (Correct answer)
Stimulator polarity

Correct answer: E1 electrode placement accuracy over the nerve

Misplacement of E1 away from the nerve trunk can attenuate amplitude without affecting latency, mimicking axonal loss.

Question 143: In a patient with peroneal nerve palsy at the fibular head, needle EMG of which muscle would help differentiate it from L5 radiculopathy?

Tibialis anterior
Peroneus longus
Extensor hallucis longus
Short head of the biceps femoris (Correct answer)

Correct answer: Short head of the biceps femoris

The short head of the biceps femoris is innervated by the peroneal division of the sciatic nerve above the fibular head; denervation there indicates a more proximal sciatic or L5 lesion, not isolated fibular head palsy.

Question 144: During setup for intraoperative neurophysiological monitoring using EMG, which mode should the system be set to for detecting spontaneous activity that indicates nerve irritation?

Single-sweep averaging mode
Triggered sweep mode with external stimulus
Repetitive stimulation mode at 3 Hz
Free-run (continuous) EMG mode (Correct answer)

Correct answer: Free-run (continuous) EMG mode

Free-run EMG continuously monitors for spontaneous activity such as neurotonic discharges that signal mechanical nerve irritation during surgery.

Question 145: An EMG technician is performing a needle exam and observes a signal that appears to be cut off at the top of the screen. What is the correct adjustment?

Decrease sensitivity (increase mV/div) (Correct answer)
Increase sweep speed
Enable the notch filter
Increase stimulator intensity

Correct answer: Decrease sensitivity (increase mV/div)

Decreasing sensitivity (larger mV/div value) expands the vertical scale so tall signals fit within the display window without clipping.

Question 146: Which part of the neuron receives incoming signals?

Axon terminal
Synaptic cleft
Dendrite (Correct answer)
Node of Ranvier

Correct answer: Dendrite

Dendrites are tree-like extensions of a neuron that receive chemical signals (neurotransmitters) from other neurons. They act as the primary input sites, converting these chemical signals into electrical impulses that are then transmitted towards the neuron's cell body.

Question 147: Prolonged P100 latency with preserved amplitude in VEPs is most characteristic of which pathological process?

Glaucomatous optic neuropathy
Demyelinating disease such as multiple sclerosis affecting the optic nerve (Correct answer)
Complete optic nerve transection
Retinal photoreceptor disease

Correct answer: Demyelinating disease such as multiple sclerosis affecting the optic nerve

Demyelination slows axonal conduction velocity, delaying the P100 latency while the amplitude may remain normal because axons are structurally intact.

Question 148: Which nerve is tested to evaluate C8/T1 radiculopathy using motor NCS?

Musculocutaneous nerve
Ulnar nerve (ADM recording) (Correct answer)
Radial nerve (EIP recording)
Median nerve (APB recording)

Correct answer: Ulnar nerve (ADM recording)

The ulnar nerve recorded from the abductor digiti minimi (ADM) primarily reflects C8/T1 myotomal innervation and is most useful for evaluating C8/T1 radiculopathy.

Question 149: Which spinal cord segment contributes to the phrenic nerve, which innervates the diaphragm?

C1–C2
C3–C5 (Correct answer)
C6–C8
T1–T4

Correct answer: C3–C5

The phrenic nerve arises from C3, C4, and C5 (mnemonic: C3, 4, 5 keeps the diaphragm alive), providing motor innervation to the diaphragm.

Question 150: Which finding on repetitive nerve stimulation (RNS) at 3 Hz indicates a postsynaptic neuromuscular junction defect such as myasthenia gravis?

Markedly prolonged CMAP duration
Incremental response >100% with high-frequency stimulation
No change in CMAP amplitude
Decremental response >10% in CMAP amplitude (Correct answer)

Correct answer: Decremental response >10% in CMAP amplitude

A decremental response greater than 10% in CMAP amplitude at 3 Hz stimulation is the hallmark of postsynaptic NMJ disorders like myasthenia gravis.

Question 151: During nerve conduction studies, repetitive nerve stimulation (RNS) at 3 Hz is being performed. The patient develops significant anxiety and requests to stop. What is the appropriate response?

Administer a sedative to reduce anxiety and continue the study
Pause immediately, reassess patient tolerance, explain the procedure again, and resume only with consent (Correct answer)
Inform the patient that stopping is not possible mid-test as it invalidates results
Reduce the stimulation rate to 1 Hz without informing the patient and continue

Correct answer: Pause immediately, reassess patient tolerance, explain the procedure again, and resume only with consent

Patients have the right to withdraw consent at any time; pausing to address concerns and re-obtaining agreement respects patient autonomy and maintains trust.

Question 152: What is the recommended inter-electrode distance between E1 and E2 for sensory nerve conduction studies using ring electrodes on a finger?

10 cm
3–4 cm (Correct answer)
1 cm
20 cm

Correct answer: 3–4 cm

Ring electrodes on adjacent finger segments are placed approximately 3–4 cm apart to ensure adequate signal separation.

Question 153: In a pediatric patient scheduled for nerve conduction studies, which modification to standard adult NCS technique is most commonly required?

Higher stimulation intensities are always needed due to thicker pediatric skin
Pediatric patients require general anesthesia for all NCS procedures
Inter-electrode distances must be adjusted downward because limb segments are shorter (Correct answer)
Surface electrode impedance requirements are relaxed for children under 10

Correct answer: Inter-electrode distances must be adjusted downward because limb segments are shorter

Shorter limb segments in children require proportionally reduced inter-electrode distances (e.g., for orthodromic sensory studies) to maintain accurate distance-based velocity calculations.

Question 154: Which NCS finding is characteristic of carpal tunnel syndrome?

Slowed peroneal motor conduction velocity
Prolonged median sensory peak latency across the wrist (Correct answer)
Reduced median motor CMAP amplitude
Absent ulnar sensory response

Correct answer: Prolonged median sensory peak latency across the wrist

Carpal tunnel syndrome characteristically shows prolonged median sensory peak latency across the wrist due to focal demyelination at the carpal tunnel.

Question 155: End-plate noise seen on needle EMG is significant because:

It indicates severe muscle disease
It indicates neuromuscular junction disease
It is a normal finding representing miniature end-plate potentials (Correct answer)
It confirms denervation at that site

Correct answer: It is a normal finding representing miniature end-plate potentials

End-plate noise consists of miniature end-plate potentials (MEPPs) and represents normal spontaneous ACh release at the neuromuscular junction, not pathology.

Question 156: Stimulus artifact in NCS is best minimized by:

Moving recording electrodes closer to the stimulator
Decreasing the low-frequency filter setting
Increasing stimulus intensity to supramaximal levels
Ensuring the ground electrode is placed between the stimulator and recording electrodes (Correct answer)

Correct answer: Ensuring the ground electrode is placed between the stimulator and recording electrodes

Placing the ground electrode between the stimulator and recording electrodes provides a current path to ground that reduces stimulus artifact contaminating the recording.

Question 157: Before performing electrodiagnostic studies on a patient taking anticoagulant therapy (e.g., warfarin), what specific precaution applies to needle EMG?

INR must be below 1.0 before any needle insertion
Superficial muscles should be prioritized; deep muscles carry higher bleeding risk (Correct answer)
The needle gauge must be larger to allow faster withdrawal
Needle EMG is absolutely contraindicated in all anticoagulated patients

Correct answer: Superficial muscles should be prioritized; deep muscles carry higher bleeding risk

In anticoagulated patients, needle EMG can still be performed, but examination of deep or paraspinal muscles with abundant blood supply increases hematoma risk and should be approached cautiously.

Question 158: In patients receiving anticoagulation therapy (e.g., warfarin), the primary concern with needle EMG is:

Electrical interference from the medication
Complete inability to perform the study
Risk of bleeding, hematoma, or compartment syndrome, particularly in deep muscles (Correct answer)
Altered nerve conduction velocities due to medication

Correct answer: Risk of bleeding, hematoma, or compartment syndrome, particularly in deep muscles

Anticoagulated patients have increased bleeding risk with needle EMG; deep muscles (paraspinals, iliopsoas) carry higher hematoma risk and should be approached cautiously.

Question 159: Which patient position is recommended when performing lower-extremity nerve conduction studies to minimize limb volume effects and ensure reproducibility?

Patient prone with knees flexed to 90 degrees
Patient supine with the limb fully supported and relaxed (Correct answer)
Patient seated upright with legs dangling
Patient standing to allow natural muscle tone

Correct answer: Patient supine with the limb fully supported and relaxed

A supine position with the limb supported and relaxed standardizes limb geometry, reduces muscle tension artifacts, and improves inter-study reproducibility.

Question 160: In evaluating tarsal tunnel syndrome, which EDX test is most useful?

Sural sensory NCS
Peroneal motor NCS at the ankle
H-reflex from the gastrocnemius
Tibial motor NCS with recording from medial and lateral plantar muscles plus plantar sensory studies (Correct answer)

Correct answer: Tibial motor NCS with recording from medial and lateral plantar muscles plus plantar sensory studies

Tarsal tunnel syndrome involves the tibial nerve at the ankle; specific plantar sensory NCS and tibial motor studies to intrinsic foot muscles help confirm and localize the lesion.

Question 161: Which SSEP finding indicates a lesion between the cervical spinal cord and the cortex?

Preserved subcortical N13 response with absent or delayed cortical N20 response (Correct answer)
Increased amplitude of the cortical response with normal latency
Absent Erb's point potential with a normal cortical N20 response
Prolonged peripheral conduction time with a normal central conduction time

Correct answer: Preserved subcortical N13 response with absent or delayed cortical N20 response

Preservation of the subcortical generator (N13) combined with loss or delay of the cortical response (N20) localizes dysfunction to the pathway between those two levels.

Question 162: In an EDX report, it is important to include which of the following to ensure reproducibility?

The technician's personal interpretation of the findings
Patient's insurance information
Electrode placement sites, distances measured, filter settings, and sweep speeds used (Correct answer)
Only the numerical values without reference ranges

Correct answer: Electrode placement sites, distances measured, filter settings, and sweep speeds used

Documenting electrode placement, measured distances, filter settings, and sweep speeds allows reproducibility and meaningful comparison with future studies.

Question 163: What is the approximate conduction velocity range for Aβ sensory fibers?

70–120 m/s
0.5–2 m/s
30–70 m/s (Correct answer)
5–15 m/s

Correct answer: 30–70 m/s

Aβ fibers are myelinated and conduct at 30–70 m/s, carrying touch and pressure information.

Question 164: Which component records electrical activity from muscles?

Surface thermometer
Stimulator
Electrode (Correct answer)
Oscilloscope

Correct answer: Electrode

Electrodes are small, conductive devices placed on the skin or inserted into muscles to detect and record the electrical activity generated by nerves and muscles. They convert these biological electrical signals into a form that can be amplified and displayed by the electrodiagnostic equipment.

Question 165: Fibrillation potentials on needle EMG represent:

Voluntary firing of normal motor units
Fasciculation of an entire motor unit
Normal insertional activity
Spontaneous discharge of individual denervated muscle fibers (Correct answer)

Correct answer: Spontaneous discharge of individual denervated muscle fibers

Fibrillation potentials represent spontaneous discharges of single denervated muscle fibers that have become hyperexcitable after losing their nerve supply.

Question 166: How should a technician position a patient for a lower limb NCS?

Standing position
Sitting upright
Leaning forward in a chair
Lying down with relaxed limbs (Correct answer)

Correct answer: Lying down with relaxed limbs

For a lower limb Nerve Conduction Study (NCS), the patient should be positioned lying down with their limbs relaxed. This position minimizes muscle tension and movement artifacts, which can interfere with accurate signal acquisition. Relaxed muscles ensure that the electrical responses being measured are primarily from the nerves, leading to more reliable and interpretable results.

Question 167: What is the purpose of using both sensory and motor nerve tests in EDX?

To assess hearing loss
To reduce exam time
To identify and classify nerve damage (Correct answer)
To check muscle strength only

Correct answer: To identify and classify nerve damage

Using both sensory and motor nerve tests in EDX provides a comprehensive assessment of nerve function. This dual approach allows clinicians to determine whether the damage affects sensory nerves, motor nerves, or both, and to classify the type and severity of nerve damage, aiding in accurate diagnosis and treatment planning.

Question 168: When comparing median and ulnar sensory latencies across the palm (palmar mixed NCS), a difference of more than __ ms is diagnostic of carpal tunnel syndrome.

0.2 ms
0.8 ms
1.2 ms
0.4 ms (Correct answer)

Correct answer: 0.4 ms

A median-ulnar palmar mixed NCS latency difference greater than 0.4 ms is considered diagnostic of carpal tunnel syndrome.

Question 169: F-wave studies are used primarily to evaluate:

Proximal motor nerve and root conduction (Correct answer)
Neuromuscular junction transmission
Autonomic nervous system function
Distal sensory nerve function

Correct answer: Proximal motor nerve and root conduction

F-waves travel antidromically to motor neurons and orthodromically back to the muscle, allowing evaluation of proximal motor nerve and spinal root integrity.

Question 170: Which type of synapse allows electrical signals to pass directly between neurons through gap junctions?

Neuromuscular junction
Electrical (electrotonic) synapse (Correct answer)
Chemical synapse
Ribbon synapse

Correct answer: Electrical (electrotonic) synapse

Electrical synapses use connexin-based gap junctions to allow direct ionic current flow between coupled cells, enabling rapid synchronous transmission.

Question 171: A lesion at the C6 spinal level most commonly results in weakness of which muscle group?

Finger extensors (wrist drop)
Wrist extensors and elbow flexors (Correct answer)
Shoulder abductors only
Intrinsic hand muscles

Correct answer: Wrist extensors and elbow flexors

C6 primarily innervates wrist extensors (extensor carpi radialis) and contributes to elbow flexors (biceps brachii, brachioradialis).

Question 172: Which type of artifact most frequently contaminates evoked potential recordings and is the most common technical challenge?

60 Hz power line interference
Muscle (EMG) artifact from patient tension or movement (Correct answer)
DC electrode drift
Cardiac R-wave artifact

Correct answer: Muscle (EMG) artifact from patient tension or movement

Muscle artifact from patient tension or involuntary movement has a broad frequency spectrum overlapping with evoked potentials, making it the predominant source of technical interference.

Question 173: Conduction block on motor nerve conduction study is defined as a CMAP amplitude reduction of greater than what percentage between proximal and distal stimulation sites?

50% (Correct answer)
20%
10%
30%

Correct answer: 50%

A proximal-to-distal CMAP amplitude drop exceeding 50% (with <15% area reduction from temporal dispersion) is the widely accepted criterion for conduction block indicating focal demyelination.

Question 174: Performing EDX studies in a patient with active skin infection or open wounds over the target area requires:

Deferring the study if possible or avoiding electrode placement in infected areas and using alternative sites to prevent spreading infection (Correct answer)
Using higher stimulus intensity to penetrate the wound
Applying conductive gel directly into the wound
Proceeding normally as infection does not affect results

Correct answer: Deferring the study if possible or avoiding electrode placement in infected areas and using alternative sites to prevent spreading infection

Placing electrodes in or near infected or open wound areas risks spreading infection; the study should be modified to use alternative sites or deferred until the skin is healed.

Question 175: During somatosensory evoked potential (SSEP) recording, the N20 component generated over the contralateral somatosensory cortex is elicited by stimulating which nerve?

Sural nerve at the ankle
Median nerve at the wrist (Correct answer)
Tibial nerve at the ankle
Peroneal nerve at the knee

Correct answer: Median nerve at the wrist

Median nerve stimulation at the wrist generates the cortical N20 response over the contralateral parietal scalp, representing thalamocortical arrival of the sensory volley.

Question 176: Which nerve is typically stimulated at the wrist to obtain upper extremity somatosensory evoked potentials (SSEPs)?

Median nerve (Correct answer)
Musculocutaneous nerve
Radial nerve
Ulnar nerve

Correct answer: Median nerve

The median nerve at the wrist is the standard stimulation site for upper extremity SSEPs due to its reliable brachial plexus and cortical responses.

Question 177: What is the significance of conduction block in a nerve conduction study?

It indicates a central nervous system disorder
It is a normal finding in older patients
It suggests focal demyelination preventing impulse propagation across a segment (Correct answer)
It indicates axonal degeneration along the entire nerve

Correct answer: It suggests focal demyelination preventing impulse propagation across a segment

Conduction block is caused by focal demyelination that prevents action potential propagation, resulting in CMAP amplitude drop of ≥50% across a nerve segment.

Question 178: A patient with diabetes mellitus presents for EDX testing. Their hands feel cool. The skin temperature is measured at 30°C. What is the correct action before beginning nerve conduction studies?

Warm the hands to at least 32°C using warm water or a heating pad before testing (Correct answer)
Cancel the study and reschedule for a warmer day
Apply correction formulas and proceed at 30°C
Proceed immediately to avoid further cooling

Correct answer: Warm the hands to at least 32°C using warm water or a heating pad before testing

Standard protocol requires limb temperature to be at least 32°C (some labs use 34°C) before NCS; warming prevents false prolongation of latencies that mimics or worsens apparent neuropathy.

Question 179: Which of the following correctly describes the purpose of increasing the number of averages in a nerve conduction study?

It improves signal-to-noise ratio by reinforcing the time-locked response while averaging out random noise (Correct answer)
It increases the stimulus intensity delivered to the nerve
It widens the filter bandwidth to capture more frequencies
It reduces the sweep speed to display more time on screen

Correct answer: It improves signal-to-noise ratio by reinforcing the time-locked response while averaging out random noise

Each sweep adds the stimulus-locked response coherently while noise, being random, partially cancels, improving the signal-to-noise ratio by the square root of the number of averages.

Question 180: During repetitive nerve stimulation, at what frequency is slow repetitive stimulation typically performed to assess neuromuscular junction disorders?

50–100 Hz
10–20 Hz
30–50 Hz
1–3 Hz (Correct answer)

Correct answer: 1–3 Hz

Slow repetitive stimulation at 2–3 Hz reveals decremental responses characteristic of postsynaptic NMJ disorders such as myasthenia gravis.

Question 181: Temperature correction in nerve conduction studies is important because:

Cooler temperatures slow conduction velocity and prolong latencies, potentially mimicking neuropathy (Correct answer)
Warmer limbs produce lower amplitude potentials
Temperature does not affect NCS parameters
Warmer temperatures cause conduction block

Correct answer: Cooler temperatures slow conduction velocity and prolong latencies, potentially mimicking neuropathy

Limb cooling slows ion channel kinetics, increasing latencies and slowing conduction velocity, which can produce false-positive findings if not recognized and corrected.

Question 182: During Wallerian degeneration, what happens to the axon distal to a nerve transection?

It regenerates immediately toward the target
It undergoes demyelination only, with axon preserved
It remains intact indefinitely
It degenerates over days to weeks as Schwann cells clear debris (Correct answer)

Correct answer: It degenerates over days to weeks as Schwann cells clear debris

After axotomy, the distal axon segment undergoes Wallerian degeneration within days to weeks; Schwann cells and macrophages phagocytose the debris, leaving the endoneurial tubes available for regrowth.

Question 183: EDX findings in critical illness myopathy (CIM) include:

Absent F-waves with normal CMAP amplitudes
Fibrillations confined to paraspinal muscles
Normal needle EMG with reduced SNAP amplitudes
Reduced CMAP amplitudes, short-duration MUPs with early recruitment, and reduced muscle membrane excitability (Correct answer)

Correct answer: Reduced CMAP amplitudes, short-duration MUPs with early recruitment, and reduced muscle membrane excitability

CIM shows reduced CMAP amplitudes (reflecting muscle membrane inexcitability), short-duration small MUPs (myopathic), and early recruitment on EMG.

Question 184: What is the approximate normal I-V interpeak latency in brainstem auditory evoked potentials?

1.5 ms
10.0 ms
8.0 ms
4.0 ms (Correct answer)

Correct answer: 4.0 ms

The I-V interpeak latency normally measures approximately 4.0 ms and reflects total conduction time through the brainstem auditory pathway from the cochlear nerve to the midbrain.

Question 185: In the brachial plexus, what do the medial, lateral, and posterior cords wrap around?

The first rib
The axillary artery (Correct answer)
The coracobrachialis muscle
The clavicle

Correct answer: The axillary artery

The three cords of the brachial plexus are named for their position relative to the second part of the axillary artery.

Question 186: What does a reduced conduction velocity in an NCS indicate?

Nerve dysfunction (Correct answer)
Improved signal strength
Stronger muscle contraction
Normal nerve response

Correct answer: Nerve dysfunction

A reduced conduction velocity in an NCS indicates that nerve impulses are traveling slower than normal along the nerve. This slowing suggests damage to the myelin sheath (demyelination) or the nerve axon itself, pointing towards various forms of nerve dysfunction or neuropathy.

Question 187: In a patient with foot drop, EDX finding of fibrillations isolated to the tibialis anterior and extensor hallucis longus with a normal short head of biceps femoris most strongly suggests:

L4 radiculopathy
Sciatic neuropathy
Common peroneal nerve palsy at the fibular head (Correct answer)
L5 radiculopathy sparing paraspinals

Correct answer: Common peroneal nerve palsy at the fibular head

Denervation limited to deep peroneal–innervated muscles (tibialis anterior, EHL) with a normal short head biceps femoris (also peroneal but above the fibular head) localizes the lesion to the fibular head.

Question 188: What is the purpose of nerve conduction studies (NCS)?

To record muscle spasms
To monitor heart rate
To detect brain tumors
To assess nerve function (Correct answer)

Correct answer: To assess nerve function

Nerve conduction studies (NCS) are diagnostic tests that measure how fast and how well electrical signals travel along a nerve. They are used to evaluate the function of motor and sensory nerves, helping to identify nerve damage or dysfunction, such as carpal tunnel syndrome or neuropathy.

Question 189: During needle EMG of the lumbar paraspinal muscles, abnormal spontaneous activity at multiple levels is most consistent with:

Normal variant in older patients
Peripheral polyneuropathy
Multilevel radiculopathy or intraspinal pathology (Correct answer)
Plexopathy distal to the posterior ramus

Correct answer: Multilevel radiculopathy or intraspinal pathology

The paraspinal muscles are innervated by the posterior primary rami proximal to the plexus; abnormality here at multiple levels suggests intraspinal or multilevel radicular pathology.

Question 190: When performing upper extremity somatosensory evoked potentials (SEPs), the recording electrode placed at Erb's point (EP) primarily monitors:

Brainstem response at the dorsal column nuclei
Cortical response at the primary somatosensory area
Peripheral nerve volley at the brachial plexus level (Correct answer)
Spinal cord response at C3–C4

Correct answer: Peripheral nerve volley at the brachial plexus level

The Erb's point electrode records the peripheral nerve action potential as the volley passes through the brachial plexus, serving as the peripheral reference for SEP interpretation.

Question 191: In a demyelinating neuropathy, which electrodiagnostic parameter is most characteristically prolonged?

Amplitude of the CMAP
Duration of the F-wave
Needle EMG insertional activity
Distal motor latency (Correct answer)

Correct answer: Distal motor latency

Loss of myelin slows conduction velocity and prolongs distal motor latency, the hallmark of a demyelinating process on NCS.

Question 192: Which safety precaution is essential before performing nerve conduction studies in a patient with an implanted cardiac pacemaker?

Only perform sensory NCS and avoid all motor studies
Consult with cardiology and avoid stimulation over the chest or neck; keep currents distal and away from the pacemaker leads (Correct answer)
Pacemaker patients cannot have NCS under any circumstances
Increase stimulus intensity to achieve supramaximal stimulation quickly

Correct answer: Consult with cardiology and avoid stimulation over the chest or neck; keep currents distal and away from the pacemaker leads

NCS can be performed safely in pacemaker patients if stimulation is kept in the extremities, away from the pacemaker generator and leads, and with prior cardiology consultation if uncertain.

Question 193: When an EDX study is technically limited due to peripheral edema or obesity, the report should:

Refuse to issue a report
Report all values as normal
Document the technical limitations and their potential impact on the study's reliability (Correct answer)
Only report values that meet normal criteria

Correct answer: Document the technical limitations and their potential impact on the study's reliability

Transparency about technical limitations (edema, obesity, inability to obtain supramaximal stimulation) is essential so the referring clinician can appropriately weight the EDX conclusions.

Question 194: The N20 component recorded over the contralateral scalp in median nerve SSEPs is generated by which structure?

Brachial plexus
Thalamus
Primary somatosensory cortex (Correct answer)
Cervical spinal cord

Correct answer: Primary somatosensory cortex

N20 is the earliest cortical response to median nerve stimulation and is generated in the contralateral primary somatosensory cortex (area 3b).

Question 195: Motor unit action potential (MUAP) duration is primarily determined by:

The number of motor neurons in the anterior horn
The velocity of the nerve impulse
The diameter of the recording needle
The spatial distribution of muscle fibers within the motor unit territory (Correct answer)

Correct answer: The spatial distribution of muscle fibers within the motor unit territory

MUAP duration reflects the spatial scatter of muscle fibers within the motor unit territory; fibers spread over a larger area produce longer-duration MUAPs.

Question 196: A blink reflex study evaluates which nerve and pathway?

Optic nerve and occipital cortex
Vagus nerve and brainstem
Facial motor nerve only
Trigeminal sensory and facial motor pathways (Correct answer)

Correct answer: Trigeminal sensory and facial motor pathways

The blink reflex evaluates the trigeminal afferent (V1) and facial efferent pathways, with R1 and R2 components reflecting brainstem and pontine circuitry.

Question 197: For an F-wave study, how should sweep speed typically be adjusted compared to a standard distal motor latency recording?

Increased to 100 ms/div or more (Correct answer)
Kept identical at 5 ms/div
Set to 10 ms/div regardless of nerve tested
Decreased to 1 ms/div

Correct answer: Increased to 100 ms/div or more

F-waves travel to the spinal cord and back, requiring a longer time window (100 ms or more) to capture the late response.

Question 198: During repetitive nerve stimulation (RNS) at 3 Hz, a decrement greater than what percentage is considered abnormal?

20%
10% (Correct answer)
5%
15%

Correct answer: 10%

A decrement exceeding 10% in CMAP amplitude from the first to the fourth or fifth response during 3 Hz RNS is considered abnormal and suggests a neuromuscular junction disorder.

Question 199: Which EMG pattern is most consistent with Lambert-Eaton Myasthenic Syndrome (LEMS) on repetitive nerve stimulation?

Decremental response at 3 Hz stimulation
Incremental response >100% at high-frequency (20–50 Hz) stimulation or post-exercise (Correct answer)
Decremental response only at high frequencies
No change in CMAP amplitude at any stimulation frequency

Correct answer: Incremental response >100% at high-frequency (20–50 Hz) stimulation or post-exercise

LEMS shows a markedly incremental CMAP response (>100%) at high-frequency stimulation or after brief exercise because calcium accumulation enhances ACh vesicle release.

Question 200: Which spinal cord tract carries proprioceptive information ipsilaterally to the cerebellum?

Dorsal columns
Corticospinal tract
Lateral spinothalamic tract
Dorsal spinocerebellar tract (Correct answer)

Correct answer: Dorsal spinocerebellar tract

The dorsal spinocerebellar tract conveys unconscious proprioceptive signals from the lower limb ipsilaterally to the cerebellum.

Question 201: What is the primary purpose of signal averaging in evoked potential recordings?

To synchronize stimulation with the cardiac cycle
To improve signal-to-noise ratio by canceling random background EEG activity (Correct answer)
To filter out frequencies above 100 Hz
To increase the intensity of the electrical stimulus

Correct answer: To improve signal-to-noise ratio by canceling random background EEG activity

Averaging enhances the time-locked evoked response while random background noise cancels out mathematically, improving SNR proportional to the square root of the number of averages.

Question 202: A patient with wrist drop after humeral fracture has EDX showing preserved radial sensory SNAP amplitude. What does this suggest?

The lesion involves the posterior cord of the brachial plexus
The lesion may be proximal to where the superficial radial sensory branch originates, sparing it (Correct answer)
Complete axonal interruption of the radial nerve
No nerve injury is present

Correct answer: The lesion may be proximal to where the superficial radial sensory branch originates, sparing it

A preserved SNAP despite motor weakness suggests the sensory branch may be anatomically spared, or the timing of testing is too early for Wallerian degeneration to cause amplitude loss.

Question 203: What is the function of the spinal cord in the nervous system?

Processes visual input
Regulates hormone release
Transmits nerve impulses and mediates reflexes (Correct answer)
Controls blood pressure

Correct answer: Transmits nerve impulses and mediates reflexes

The spinal cord serves as the main pathway for information transmission between the brain and the rest of the body. It carries motor commands from the brain to muscles and sensory information from the body to the brain, and it also independently mediates rapid, involuntary reflex actions.

Question 204: In a patient with suspected thoracic outlet syndrome (neurogenic type), which NCS finding is most characteristic?

Reduced medial antebrachial cutaneous SNAP amplitude (Correct answer)
Reduced ulnar sensory amplitude with normal ulnar motor amplitude
Prolonged median motor distal latency
Absent F-waves in the median nerve

Correct answer: Reduced medial antebrachial cutaneous SNAP amplitude

Neurogenic TOS characteristically shows reduced medial antebrachial cutaneous SNAP amplitude due to compression of the lower trunk/medial cord of the brachial plexus.

Question 205: When a patient's CMAP or SNAP amplitude is unexpectedly low, the first technical factor to assess is:

Whether the recording electrodes have adequate skin contact and low impedance (Correct answer)
Whether the repetition rate is too fast
Whether the filter bandwidth is set to 20 Hz–10 kHz
Whether the sweep speed is set correctly

Correct answer: Whether the recording electrodes have adequate skin contact and low impedance

High electrode impedance due to poor skin contact is one of the most common technical causes of reduced CMAP or SNAP amplitude and should be checked before concluding pathology.

Question 206: Which neurotransmitter is released at the neuromuscular junction?

Serotonin
Dopamine
Acetylcholine (Correct answer)
Norepinephrine

Correct answer: Acetylcholine

Acetylcholine is released from motor nerve terminals and binds nicotinic receptors on the motor end plate to trigger muscle depolarization.

Question 207: Which EDX finding best differentiates cervical radiculopathy from brachial plexopathy?

Reduced SNAP amplitude in the distribution of the affected root
Abnormal needle EMG in paraspinal muscles at the affected spinal level (Correct answer)
Reduced CMAP amplitude in the affected muscles
Prolonged F-wave latencies in the affected limb

Correct answer: Abnormal needle EMG in paraspinal muscles at the affected spinal level

Paraspinal muscle denervation at the affected level is seen only in radiculopathy because the posterior primary ramus arises proximal to the plexus.

Question 208: Which filter setting change would most reduce high-frequency artifact during EMG needle examination?

Lower the high-frequency filter from 10 kHz to 2 kHz (Correct answer)
Increase gain from 50 µV to 200 µV
Decrease sweep speed from 10 ms to 5 ms
Raise the low-frequency filter from 10 Hz to 500 Hz

Correct answer: Lower the high-frequency filter from 10 kHz to 2 kHz

Lowering the high-frequency (low-pass) filter reduces high-frequency noise and artifact while preserving the essential components of motor unit potentials.

Question 209: Which click stimulus polarity is most commonly used clinically for BAEPs to minimize stimulus artifact?

Silence baseline with no polarity
Rarefaction polarity only
Condensation polarity only
Alternating polarity (Correct answer)

Correct answer: Alternating polarity

Alternating polarity cancels the cochlear microphonic and reduces stimulus artifact by averaging responses to opposite-polarity clicks, preserving the neural response.

Question 210: A patient with a pacemaker is referred for nerve conduction studies. What is the primary safety concern?

The patient cannot lie still long enough for accurate recordings
Repetitive stimulation will drain the pacemaker battery
The pacemaker will interfere with EMG amplifier gain settings
Electrical stimulation current may inhibit or reset the pacemaker (Correct answer)

Correct answer: Electrical stimulation current may inhibit or reset the pacemaker

External electrical stimulation can be sensed by a pacemaker's sensing circuit and may trigger inappropriate inhibition or mode-switching, posing a cardiac risk.

Question 211: Which structure in the spinal cord carries decussated pain and temperature signals to the thalamus?

Dorsal columns (posterior funiculus)
Lateral spinothalamic tract (Correct answer)
Dorsal spinocerebellar tract
Corticospinal tract

Correct answer: Lateral spinothalamic tract

The lateral spinothalamic tract crosses within 1–2 spinal levels of entry and ascends contralaterally carrying pain and temperature to the thalamus.

Question 212: In evaluating a patient with vasculitic neuropathy, EDX findings typically demonstrate:

Normal NCS with myopathic EMG
Diffuse uniform demyelination
Asymmetric, multifocal axonal sensorimotor neuropathy (mononeuritis multiplex pattern) (Correct answer)
Symmetric length-dependent polyneuropathy identical to diabetic neuropathy

Correct answer: Asymmetric, multifocal axonal sensorimotor neuropathy (mononeuritis multiplex pattern)

Vasculitic neuropathy causes ischemic axonal injury to individual nerves in a random multifocal pattern (mononeuritis multiplex), resulting in asymmetric axonal sensorimotor findings on EDX.

Question 213: What should a technician do if a patient expresses anxiety before a test?

Rush the exam
Ignore the anxiety
Explain the procedure calmly (Correct answer)
Refer them to billing

Correct answer: Explain the procedure calmly

If a patient expresses anxiety before a test, the technician's role is to provide reassurance and clarity. Calmly explaining the procedure in simple terms, addressing their concerns, and setting realistic expectations can significantly alleviate patient anxiety. This empathetic approach fosters trust and cooperation, leading to a more comfortable and successful examination.

Question 214: What is a motor unit action potential (MUAP)?

Muscle fiber response from one motor neuron (Correct answer)
Spinal reflex arc
Heart rhythm signal
Brain wave pattern

Correct answer: Muscle fiber response from one motor neuron

A motor unit action potential (MUAP) is the electrical signal recorded from a group of muscle fibers that are innervated by a single motor neuron. When a motor neuron fires, all the muscle fibers it controls contract simultaneously, generating a characteristic electrical potential that can be measured during EMG.

Question 215: When recording a sensory nerve action potential (SNAP), which measurement is taken from the baseline to the negative peak?

Area
Duration
Onset amplitude
Peak amplitude (Correct answer)

Correct answer: Peak amplitude

The peak amplitude of a SNAP is measured from the baseline to the highest point of the negative peak of the waveform.

Question 216: A technician is about to perform H-reflex studies and notes the patient's record indicates a history of DVT in the same leg. What is the safest approach?

Proceed normally; H-reflex studies pose no DVT risk
Switch to the contralateral limb without notifying anyone
Consult with the referring physician before applying pressure from electrode straps or positioning maneuvers to the affected limb (Correct answer)
Cancel the entire study and refer back to the ordering physician

Correct answer: Consult with the referring physician before applying pressure from electrode straps or positioning maneuvers to the affected limb

Pressure from electrode straps or limb positioning could theoretically dislodge a thrombus; notifying the referring physician to clarify safety constraints is the appropriate step before proceeding.

Question 217: Which EDX pattern is most consistent with a diagnosis of Guillain-Barré syndrome (acute inflammatory demyelinating polyneuropathy)?

Length-dependent axonal polyneuropathy with distal sensory loss
Axonal loss with active denervation on EMG
Normal NCS with myopathic EMG
Diffuse demyelination with prolonged distal latencies, slow conduction velocities, and absent F-waves (Correct answer)

Correct answer: Diffuse demyelination with prolonged distal latencies, slow conduction velocities, and absent F-waves

AIDP/GBS shows widespread demyelination including absent F-waves, prolonged distal latencies, slow conduction velocities, and conduction block.

Question 218: Which nerve conduction parameter is most affected by limb temperature, increasing as temperature decreases?

Area under the curve only
Number of phases in the waveform
Distal latency and duration (Correct answer)
Amplitude only

Correct answer: Distal latency and duration

Cooling slows sodium channel kinetics, prolonging distal latency and increasing duration of nerve conduction potentials; amplitude may also increase due to reduced temporal dispersion.

Question 219: Saltatory conduction in myelinated nerves occurs because action potentials jump between which structures?

Synaptic terminals
Nodes of Ranvier (Correct answer)
Axon hillocks
Dendrites

Correct answer: Nodes of Ranvier

In myelinated fibers, depolarization skips from one node of Ranvier to the next, dramatically increasing conduction velocity.

Question 220: During a median nerve motor study, the recording technician notes that the initial deflection of the CMAP is positive (downward). This most likely indicates:

The sweep speed is set too fast
The stimulus intensity is submaximal
The nerve is demyelinated proximally
E1 is not positioned over the motor point of the muscle (Correct answer)

Correct answer: E1 is not positioned over the motor point of the muscle

A positive initial deflection indicates E1 is displaced from the motor point, causing the recording to pick up a far-field potential before the approaching depolarization reaches E1.

Question 221: When calibrating an EMG machine before use, which parameter confirms that the amplifier gain is accurate?

The stimulator output matches the displayed mA value only
A known calibration signal produces the expected deflection height on screen (Correct answer)
The sweep speed matches the selected setting on the display
The notch filter reduces ambient noise to zero

Correct answer: A known calibration signal produces the expected deflection height on screen

Applying a known calibration pulse and verifying the waveform height confirms that the amplifier gain is set correctly.

Question 222: During a facial nerve NCS, a patient becomes distressed and reports eye pain after a surface electrode is placed near the orbit. What should the technician do immediately?

Remove the electrode, inspect for electrode gel contact with the eye, and address the complaint before proceeding (Correct answer)
Place a cotton eye pad over the area and proceed with recording
Reduce stimulator output and continue to save procedural time
Reassure the patient that orbital discomfort is normal and continue the study

Correct answer: Remove the electrode, inspect for electrode gel contact with the eye, and address the complaint before proceeding

Electrode gel near or in the eye can cause corneal irritation or chemical injury; the electrode must be removed, the eye assessed, and the patient's comfort ensured before any further testing.

Question 223: What is the recommended minimum number of averages for reliable cortical SSEP recording, with replication required?

200–500 averages (Correct answer)
10–20 averages
1000–2000 averages
50–100 averages

Correct answer: 200–500 averages

A minimum of 200–500 averages is needed to achieve adequate signal-to-noise ratio for cortical SSEPs, and replication of the waveform confirms reproducibility.

Question 224: What role does the synapse play in neuronal communication?

Regulates oxygen supply
Stores myelin
Facilitates signal transmission between neurons (Correct answer)
Generates impulses

Correct answer: Facilitates signal transmission between neurons

A synapse is the specialized junction where one neuron communicates with another neuron or an effector cell. It involves the transmission of nerve impulses, typically via neurotransmitters, from the presynaptic neuron across the synaptic cleft to the postsynaptic neuron, allowing for complex neural networks.

Question 225: EDX studies in pediatric patients may require sedation because:

Pediatric patients have absolute contraindications to awake NCS
Movement and poor cooperation can produce artifact and make needle EMG technically unreliable (Correct answer)
Sedation increases SNAP amplitudes in children
Nerve conduction velocities cannot be measured without sedation

Correct answer: Movement and poor cooperation can produce artifact and make needle EMG technically unreliable

Children may not cooperate with voluntary relaxation or contraction needed for EMG; movement artifact and lack of cooperation can significantly compromise study quality.

Question 226: During ulnar motor nerve conduction, which muscle is used as the standard recording site?

First dorsal interosseous
Flexor carpi ulnaris
Hypothenar eminence broadly
Abductor digiti minimi (Correct answer)

Correct answer: Abductor digiti minimi

The abductor digiti minimi (ADM) is the standard recording muscle for ulnar motor nerve conduction studies due to its reliable anatomy and consistent innervation.

Question 227: What is the purpose of the reference (E2) electrode in a sensory nerve conduction study?

To provide the electrical ground for the patient
To serve as an inactive site for differential amplification, canceling common-mode noise (Correct answer)
To measure skin temperature at the recording site
To stimulate the nerve antidromically

Correct answer: To serve as an inactive site for differential amplification, canceling common-mode noise

The reference electrode feeds into the inverting input of the differential amplifier, which subtracts shared noise and amplifies only the signal of interest.

Question 228: When performing EDX studies in a patient with suspected acute Guillain-Barré syndrome within the first week of symptom onset, results may be:

Always dramatically abnormal from day one
Consistent with a pure axonal pattern immediately
Initially normal or show only subtle F-wave abnormalities, as demyelination evolves over days to weeks (Correct answer)
Show marked denervation on needle EMG within 24 hours

Correct answer: Initially normal or show only subtle F-wave abnormalities, as demyelination evolves over days to weeks

In early GBS, EDX changes lag behind clinical presentation; absent or prolonged F-waves may be the only early finding, with full demyelinating pattern emerging over 1–4 weeks.

Question 229: When is the H-reflex most clinically useful in EDX testing?

Evaluating ulnar neuropathy
Evaluating S1 radiculopathy (Correct answer)
Evaluating carpal tunnel syndrome
Evaluating C6 radiculopathy

Correct answer: Evaluating S1 radiculopathy

The H-reflex evaluates the S1 reflex arc (tibial nerve, S1 root, gastrocnemius/soleus), making it the most sensitive NCS measure for S1 radiculopathy.

Question 230: A patient undergoing electrodiagnostic testing has an automatic implantable cardioverter-defibrillator (AICD). Which statement about performing NCS on this patient is most accurate?

NCS is safe in AICD patients only when using subthreshold stimulation intensities
AICD patients require the device to be inactivated by a cardiologist for all NCS sessions
NCS may be performed with caution, keeping stimulation sites away from the device and leads, and monitoring cardiac status (Correct answer)
NCS is absolutely contraindicated in all patients with an AICD

Correct answer: NCS may be performed with caution, keeping stimulation sites away from the device and leads, and monitoring cardiac status

NCS can generally be performed in AICD patients by avoiding stimulation over or near the device/leads and ensuring cardiac monitoring is available, though cardiologist input should be sought for high-risk cases.

Question 231: What analysis time (sweep duration) is typically used for upper extremity median nerve SSEP recordings?

500 ms
200 ms
50–60 ms (Correct answer)
1–2 ms

Correct answer: 50–60 ms

A sweep of 50–60 ms is standard for upper extremity SSEPs because it captures all relevant components from the Erb's point potential through the cortical N20/P23, with an adequate pre-stimulus baseline.

Question 232: When evaluating a patient with hypothyroidism for peripheral neuropathy, EDX most commonly shows:

Prolonged distal latencies (especially median), reduced SNAP amplitudes, and mild slowing consistent with entrapment neuropathy or axonal polyneuropathy (Correct answer)
Absent SNAPs with normal motor NCS
Myotonic discharges exclusively
Normal EDX in all hypothyroid patients

Correct answer: Prolonged distal latencies (especially median), reduced SNAP amplitudes, and mild slowing consistent with entrapment neuropathy or axonal polyneuropathy

Hypothyroidism predisposes to carpal tunnel syndrome (prolonged median distal latency) and can cause axonal polyneuropathy with reduced SNAP amplitudes and mild velocity slowing.

Question 233: Which of the following is a typical setting for EDX testing?

Operating room
Neurology clinic (Correct answer)
Pharmacy
Radiology suite

Correct answer: Neurology clinic

Electrodiagnostic (EDX) testing, which includes NCS and electromyography (EMG), is typically performed in a neurology clinic or a specialized neurophysiology lab. These settings are equipped with the necessary specialized equipment and staffed by neurologists or trained technicians who interpret the results.

Question 234: What is the standard inter-stimulus interval used during slow repetitive nerve stimulation (RNS) to assess neuromuscular junction disorders?

333 ms (3 Hz) (Correct answer)
1000 ms (1 Hz)
100 ms (10 Hz)
50 ms (20 Hz)

Correct answer: 333 ms (3 Hz)

Slow RNS is performed at 3 Hz (one stimulus every 333 ms) to demonstrate decremental responses characteristic of postsynaptic NMJ disorders such as myasthenia gravis.

Question 235: Volume conduction artifacts on SNAP recordings can be reduced by:

Using near-nerve needle electrodes or ring electrodes with standardized technique (Correct answer)
Increasing the distance between active and reference electrodes
Increasing the high-frequency filter cutoff
Applying maximal stimulus intensity

Correct answer: Using near-nerve needle electrodes or ring electrodes with standardized technique

Near-nerve needle electrodes or ring electrodes with proper placement minimize volume-conducted signals from adjacent nerves and improve SNAP recording specificity.

Question 236: Which ground electrode placement is preferred during lower extremity nerve conduction studies to minimize stimulus artifact?

Over the iliac crest
Between the stimulating and recording electrodes on the same limb (Correct answer)
On the dorsum of the hand
On the contralateral leg

Correct answer: Between the stimulating and recording electrodes on the same limb

Placing the ground between the stimulator and recording electrodes intercepts and dissipates stimulus artifact before it reaches the recording site.

Question 237: What is the effect of a low skin temperature on nerve conduction velocity measurements?

Velocity increases and latencies shorten
Amplitude decreases without affecting velocity
No significant effect on velocity
Velocity decreases and latencies prolong (Correct answer)

Correct answer: Velocity decreases and latencies prolong

Cold temperatures slow ion channel kinetics, reducing conduction velocity and prolonging latencies by approximately 1–2 m/s per degree Celsius.

Question 238: When performing nerve conduction studies in neonates and infants, conduction velocities are expected to be:

Approximately half of adult values, reaching adult levels by age 3–5 years (Correct answer)
Similar to adult values due to full myelination at birth
Faster than adult values due to smaller nerve diameter
Highly variable and cannot be interpreted

Correct answer: Approximately half of adult values, reaching adult levels by age 3–5 years

Myelination is incomplete at birth; neonatal conduction velocities are approximately 50% of adult values and reach adult levels by age 3–5 years as myelination completes.

Question 239: In patients with lymphedema following mastectomy, EDX of the ipsilateral upper extremity requires caution because:

All NCS responses will be absent
There is risk of introducing infection or worsening lymphedema with needle insertion; surface techniques are preferred (Correct answer)
Conduction velocities are always faster in lymphedematous limbs
NCS results will always show false-positive demyelination

Correct answer: There is risk of introducing infection or worsening lymphedema with needle insertion; surface techniques are preferred

Needle EMG in a lymphedematous extremity post-mastectomy carries infection risk; the referring clinician should be consulted and non-invasive techniques prioritized where possible.

Question 240: The normal range for median motor distal latency in adults is approximately:

1–2 ms
8–10 ms
2–4 ms (Correct answer)
5–7 ms

Correct answer: 2–4 ms

Median motor distal latency is normally 2–4 ms; values above 4.4 ms are generally considered abnormal for carpal tunnel syndrome evaluation.

Question 241: In ALS, sensory nerve conduction studies are typically:

Absent in lower extremities only
Markedly abnormal in all extremities
Slowed without amplitude reduction
Normal or minimally abnormal, as ALS primarily affects motor neurons (Correct answer)

Correct answer: Normal or minimally abnormal, as ALS primarily affects motor neurons

ALS is primarily a motor neuron disease; sensory NCS are typically normal because sensory neurons and their axons are largely spared.

Question 242: Which artifact appears as a large deflection coinciding with each heartbeat and is best eliminated by repositioning the ground electrode?

EKG artifact (Correct answer)
60 Hz interference
Movement artifact
Electrode pop artifact

Correct answer: EKG artifact

EKG (cardiac) artifact appears rhythmically with the patient's heartbeat and can often be reduced by repositioning the ground electrode between the active electrode and the heart.

Question 243: Which evoked potential modality is the most widely used for intraoperative monitoring during spinal cord and spinal column surgery?

Cognitive event-related potentials (P300)
Visual evoked potentials (VEPs)
Brainstem auditory evoked potentials (BAEPs)
Somatosensory evoked potentials (SSEPs) (Correct answer)

Correct answer: Somatosensory evoked potentials (SSEPs)

SSEPs monitor the integrity of the dorsal column-medial lemniscal pathway and are the established standard for intraoperative neurophysiological monitoring during spinal surgery.

Question 244: During a nerve conduction study, a patient suddenly complains of dizziness and diaphoresis after electrode placement. The most likely cause is:

A vasovagal response triggered by anxiety or pain (Correct answer)
Hypersensitivity to electrode gel chemicals
Electrical leakage current from the stimulator
Electrode impedance mismatch causing artifact

Correct answer: A vasovagal response triggered by anxiety or pain

Vasovagal syncope is the most common acute patient reaction in the EDX lab, caused by anxiety or pain-induced vagal activation resulting in bradycardia and hypotension.

Question 245: When performing a median nerve motor study, which filter settings are most appropriate for recording the CMAP?

High-pass 2 Hz, low-pass 10 kHz (Correct answer)
High-pass 100 Hz, low-pass 3 kHz
High-pass 20 Hz, low-pass 500 Hz
High-pass 500 Hz, low-pass 10 kHz

Correct answer: High-pass 2 Hz, low-pass 10 kHz

Motor NCS uses a bandpass of 2–10,000 Hz to capture the full frequency range of compound muscle action potentials.

Question 246: Which measurement on nerve conduction studies best reflects the number of functioning axons?

Conduction velocity
F-wave persistence
Distal latency
CMAP or SNAP amplitude (Correct answer)

Correct answer: CMAP or SNAP amplitude

The amplitude of the compound muscle action potential (CMAP) or sensory nerve action potential (SNAP) reflects the number of activated axons and is reduced in axonal loss.

Question 247: Which control adjusts the amplitude of the signal displayed on-screen?

Gain (Correct answer)
Time base
Display contrast
Filter

Correct answer: Gain

The gain control on an EDX machine directly adjusts the amplification of the electrical signal received from the patient. By increasing the gain, smaller signals become larger and more visible on the screen, while decreasing it can prevent larger signals from saturating the display. This adjustment is critical for optimizing the visualization of nerve and muscle responses, ensuring they are clearly discernible for analysis.

Electrodiagnostic Technician (EDT) Certification

The EDT certification validates the knowledge and skills of technicians who perform electrodiagnostic studies including electromyography (EMG) and nerve conduction studies (NCS), covering device operation, waveform interpretation, quality assurance, and patient safety across diverse populations.

250

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240 min

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