EDT EDT Nerve Conduction Studies Interpretation 1 — Questions and Answers
Question 1: What does a prolonged distal latency in a motor nerve conduction study primarily indicate?
- Slowed conduction at the distal segment, suggesting demyelination (Correct answer)
- Axonal loss at the motor neuron
- Increased amplitude of the CMAP
- Normal variation in conduction velocity
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 2: In a sensory nerve conduction study, which parameter is most sensitive for detecting early axonal loss?
- Conduction velocity
- Distal latency
- Amplitude of the SNAP (Correct answer)
- 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 3: A compound muscle action potential (CMAP) with normal distal latency but reduced amplitude most likely indicates:
- Demyelinating neuropathy
- Axonal motor neuropathy (Correct answer)
- Neuromuscular junction disorder
- Central nervous system lesion
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 4: Which NCS finding is characteristic of carpal tunnel syndrome?
- Reduced median motor CMAP amplitude
- Prolonged median sensory peak latency across the wrist (Correct answer)
- Absent ulnar sensory response
- Slowed peroneal motor conduction velocity
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 5: Temporal dispersion in a motor nerve conduction study refers to:
- Increased CMAP amplitude with repetitive stimulation
- Broadening and reduction of CMAP with proximal stimulation (Correct answer)
- Absent F-waves bilaterally
- Increased conduction velocity across a segment
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 6: In ulnar neuropathy at the elbow, the most diagnostic NCS finding is:
- Absent ulnar sensory response at the wrist
- Focal slowing of ulnar motor conduction velocity across the elbow segment (Correct answer)
- Prolonged median distal motor latency
- Reduced radial sensory amplitude
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.
EDT EDT Nerve Conduction Studies Interpretation 1
What does a prolonged distal latency in a motor nerve conduction study primarily indicate?