EDT EDT Nerve Conduction Studies Interpretation 2 — Questions and Answers
Question 1: What is the significance of conduction block in a nerve conduction study?
- It indicates axonal degeneration along the entire nerve
- It suggests focal demyelination preventing impulse propagation across a segment (Correct answer)
- It is a normal finding in older patients
- It indicates a central nervous system disorder
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 2: F-wave studies are used primarily to evaluate:
- Distal sensory nerve function
- Proximal motor nerve and root conduction (Correct answer)
- Neuromuscular junction transmission
- Autonomic nervous system 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 3: When is the H-reflex most clinically useful in EDX testing?
- Evaluating C6 radiculopathy
- Evaluating S1 radiculopathy (Correct answer)
- Evaluating carpal tunnel syndrome
- Evaluating ulnar neuropathy
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 4: In a patient with polyneuropathy, which pattern of NCS abnormalities suggests primary demyelination?
- Symmetric reduction in CMAP and SNAP amplitudes
- Uniform slowing of conduction velocities with prolonged distal latencies (Correct answer)
- Absent F-waves with normal distal latencies
- 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 5: The normal range for median motor distal latency in adults is approximately:
- 1–2 ms
- 2–4 ms (Correct answer)
- 5–7 ms
- 8–10 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 6: Which nerve is tested to evaluate C8/T1 radiculopathy using motor NCS?
- Median nerve (APB recording)
- Ulnar nerve (ADM recording) (Correct answer)
- Radial nerve (EIP recording)
- Musculocutaneous nerve
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.
EDT EDT Nerve Conduction Studies Interpretation 2
What is the significance of conduction block in a nerve conduction study?