Nerve and muscle: nerve conduction studies: practice question

A Physiology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Physiology · Nerve and muscle: nerve conduction studies

Sample item

A nerve conduction study in a patient with progressive limb weakness shows markedly reduced compound muscle action potential amplitude with only slightly reduced conduction velocity. Which pathology does this pattern favour?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

D. Axonal loss

Reduced amplitude with near-normal velocity indicates loss of axons, since fewer fibres conduct the response while the survivors conduct normally. Demyelination slows conduction markedly, prolongs latency and causes conduction block without early amplitude loss.

Option by option

  • A. Primary myopathy

    Primary myopathy has normal nerve conduction studies and abnormal EMG with small motor units.

  • B. Segmental demyelination

    Demyelination gives marked slowing of velocity and prolonged latency.

  • C. Neuromuscular junction blockade

    Neuromuscular junction disorders show decrement or increment on repetitive stimulation with normal nerve conduction.

  • D. Axonal loss (correct)

    Correct. Low amplitude with preserved velocity points to axon loss.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is D, Axonal loss. Reduced amplitude with near-normal velocity indicates loss of axons, since fewer fibres conduct the response while the survivors conduct normally.

Why is "Primary myopathy" not the answer?

Primary myopathy has normal nerve conduction studies and abnormal EMG with small motor units.

Why is "Segmental demyelination" not the answer?

Demyelination gives marked slowing of velocity and prolonged latency.

Why is "Neuromuscular junction blockade" not the answer?

Neuromuscular junction disorders show decrement or increment on repetitive stimulation with normal nerve conduction.

What concept does this question test?

It tests Nerve and muscle: nerve conduction studies in Physiology. Demyelination slows conduction markedly, prolongs latency and causes conduction block without early amplitude loss.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Nerve and muscle: nerve conduction studies?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.