Neurophysiology: lower motor neurone lesion: 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 · Neurophysiology: lower motor neurone lesion

Sample item

A 3-year-old unvaccinated child has fever followed by sudden asymmetrical weakness of the right leg. On examination there is reduced tone, absent knee and ankle jerks and a flexor plantar response. Which additional findings are expected with this lesion?

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

The answer and the reasoning

D. Fasciculations and rapid muscle wasting from loss of trophic input

Poliovirus destroys anterior horn cells, producing a lower motor neurone lesion with flaccid weakness, areflexia, fasciculations and marked early atrophy because of denervation. In upper motor neurone lesions tone is increased, reflexes are brisk and the plantar response is extensor, with only disuse atrophy later.

Option by option

  • A. Spasticity with clasp-knife rigidity and brisk reflexes

    Spasticity and brisk reflexes are upper motor neurone signs.

  • B. Extensor plantar response with preserved bulk

    An extensor plantar response with preserved bulk is characteristic of an upper motor neurone lesion.

  • C. Clonus and emotional lability

    Clonus and emotional lability suggest an upper motor neurone or pseudobulbar lesion.

  • D. Fasciculations and rapid muscle wasting from loss of trophic input (correct)

    Correct. Denervation gives atrophy and fasciculations.

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, Fasciculations and rapid muscle wasting from loss of trophic input. Poliovirus destroys anterior horn cells, producing a lower motor neurone lesion with flaccid weakness, areflexia, fasciculations and marked early atrophy because of denervation.

Why is "Spasticity with clasp-knife rigidity and brisk reflexes" not the answer?

Spasticity and brisk reflexes are upper motor neurone signs.

Why is "Extensor plantar response with preserved bulk" not the answer?

An extensor plantar response with preserved bulk is characteristic of an upper motor neurone lesion.

Why is "Clonus and emotional lability" not the answer?

Clonus and emotional lability suggest an upper motor neurone or pseudobulbar lesion.

What concept does this question test?

It tests Neurophysiology: lower motor neurone lesion in Physiology. In upper motor neurone lesions tone is increased, reflexes are brisk and the plantar response is extensor, with only disuse atrophy later.

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 Neurophysiology: lower motor neurone lesion?

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.