EDT EDT EMG Waveform Analysis 2 — Questions and Answers
Question 1: Myotonic discharges on needle EMG are characterized by:
- Constant frequency and amplitude
- Waxing and waning frequency and amplitude producing a dive-bomber sound (Correct answer)
- Single high-amplitude bursts at rest
- Decremental response to repetitive nerve stimulation
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 2: In needle EMG, the term 'reduced recruitment' means:
- Too many motor units firing for the level of force exerted
- Fewer motor units than expected are available to fire, reflecting motor unit loss (Correct answer)
- Motor units that fire irregularly
- Absence of all voluntary activity
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 3: End-plate noise seen on needle EMG is significant because:
- It indicates severe muscle disease
- It is a normal finding representing miniature end-plate potentials (Correct answer)
- It confirms denervation at that site
- It indicates neuromuscular junction disease
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 4: A needle EMG finding of increased polyphasia (>20% polyphasic MUPs) in a muscle indicates:
- Normal voluntary activity in trained athletes
- Possible pathology suggesting reinnervation or myopathy causing desynchronized fiber firing (Correct answer)
- Definitive diagnosis of ALS
- 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 5: Which EMG finding in paraspinal muscles supports a diagnosis of radiculopathy rather than plexopathy?
- Fibrillations in limb muscles only
- Fibrillations and PSWs in paraspinal muscles at the affected level (Correct answer)
- Large polyphasic MUPs in distal muscles
- Absent H-reflex
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 6: Motor unit action potential (MUAP) duration is primarily determined by:
- The number of motor neurons in the anterior horn
- The spatial distribution of muscle fibers within the motor unit territory (Correct answer)
- The diameter of the recording needle
- The velocity of the nerve impulse
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.
EDT EDT EMG Waveform Analysis 2
Myotonic discharges on needle EMG are characterized by: