General anatomy: peripheral nerve injury: practice question

A Anatomy 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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Anatomy · General anatomy: peripheral nerve injury

Sample item

After a closed crush injury to the arm, a 30-year-old man has wrist drop. At 3 weeks, electromyography shows fibrillation potentials in the denervated muscles, and the nerve sheaths are in continuity. What is the injury and expected recovery?

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

The answer and the reasoning

B. Axonotmesis, with regrowth at about 1 mm per day along intact endoneurial tubes

In axonotmesis the axon and myelin are disrupted but the endoneurium, perineurium and epineurium remain, so Wallerian degeneration occurs distally and axons regrow along the intact tubes at about 1 mm per day. Fibrillation potentials at 2 to 3 weeks indicate axonal loss, which does not occur in neurapraxia. Neurotmesis is complete transection that needs surgery.

Option by option

  • A. Neurapraxia, with recovery in days to weeks because the axon is preserved

    Neurapraxia is a conduction block without axonal loss, so fibrillations and Wallerian degeneration do not appear.

  • B. Axonotmesis, with regrowth at about 1 mm per day along intact endoneurial tubes (correct)

    Correct. Axonal loss with preserved sheaths regenerates slowly, at roughly 1 mm per day.

  • C. Axonotmesis, with regrowth at about 1 cm per day along intact endoneurial tubes

    The category is right but the rate is overstated by a factor of 10; regeneration is about 1 mm per day.

  • D. Neurotmesis, with no recovery unless the nerve is surgically repaired

    Neurotmesis involves loss of continuity of the connective tissue sheaths, which is not described here.

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 Anatomy question

What is the answer to this Anatomy question?

The best answer is B, Axonotmesis, with regrowth at about 1 mm per day along intact endoneurial tubes. In axonotmesis the axon and myelin are disrupted but the endoneurium, perineurium and epineurium remain, so Wallerian degeneration occurs distally and axons regrow along the intact tubes at about 1 mm per day.

Why is "Neurapraxia, with recovery in days to weeks because the axon is prese…" not the answer?

Neurapraxia is a conduction block without axonal loss, so fibrillations and Wallerian degeneration do not appear.

Why is "Axonotmesis, with regrowth at about 1 cm per day along intact endoneu…" not the answer?

The category is right but the rate is overstated by a factor of 10; regeneration is about 1 mm per day.

Why is "Neurotmesis, with no recovery unless the nerve is surgically repaired" not the answer?

Neurotmesis involves loss of continuity of the connective tissue sheaths, which is not described here.

What concept does this question test?

It tests General anatomy: peripheral nerve injury in Anatomy. Fibrillation potentials at 2 to 3 weeks indicate axonal loss, which does not occur in neurapraxia. Neurotmesis is complete transection that needs surgery.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. 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 General anatomy: peripheral nerve injury?

Learn every nerve by its route, its muscles and what a lesion looks like at the bedside. That one habit answers a large share of questions. Then use the flashcards and the other Anatomy 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.