EDT EDX Testing Techniques 2 — Questions and Answers
Question 1: 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 2: 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)
- Raise the low-frequency filter from 10 Hz to 500 Hz
- Increase gain from 50 µV to 200 µV
- Decrease sweep speed from 10 ms to 5 ms
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 3: An H-reflex is most reliably elicited in adults by stimulating which nerve?
- Tibial nerve at the popliteal fossa (Correct answer)
- Peroneal nerve at the fibular head
- Sural nerve at the ankle
- Femoral nerve at the groin
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 4: What is the primary purpose of applying a ground electrode during nerve conduction studies?
- Reduce common-mode electrical noise and improve signal quality (Correct answer)
- Increase the amplitude of the recorded potential
- Shorten the distal latency measurement
- Prevent patient burns at the stimulation site
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 5: During repetitive nerve stimulation (RNS) at 3 Hz, a decrement greater than what percentage is considered abnormal?
- 10% (Correct answer)
- 5%
- 15%
- 20%
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 6: Which nerve conduction parameter is most affected by limb temperature, increasing as temperature decreases?
- Distal latency and duration (Correct answer)
- Amplitude only
- Area under the curve only
- Number of phases in the waveform
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 7: When recording a sensory nerve action potential (SNAP), which measurement is taken from the baseline to the negative peak?
- Peak amplitude (Correct answer)
- Onset amplitude
- Area
- Duration
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.
EDT EDX Testing Techniques 2
When performing median motor nerve conduction studies, the active (G1) electrode is placed over which landmark?