Neuroanatomy: subacute combined degeneration: 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 · Neuroanatomy: subacute combined degeneration

Sample item

A 58-year-old strict vegan has tingling in both feet, loss of vibration and joint position sense, spastic weakness of the legs, brisk knee jerks and extensor plantar responses. He is anaemic with a raised mean corpuscular volume. Which pair of spinal cord tracts is chiefly degenerating?

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

The answer and the reasoning

A. Dorsal columns and corticospinal tracts

Vitamin B12 deficiency causes subacute combined degeneration, a demyelination of the dorsal columns and the lateral corticospinal tracts. The dorsal column loss explains the impaired vibration and position sense, and the corticospinal loss explains the spasticity and extensor plantars. Pain and temperature sensation are usually spared.

Option by option

  • A. Dorsal columns and corticospinal tracts (correct)

    Correct. Dorsal column loss gives the sensory ataxia and corticospinal loss gives the spastic weakness with extensor plantars.

  • B. Anterior horns and spinocerebellar tracts

    Anterior horn loss gives wasted, flaccid weakness rather than spasticity, and spinocerebellar damage does not explain loss of vibration sense.

  • C. Dorsal columns and spinothalamic tracts

    The dorsal column loss is correct, but spinothalamic fibres are usually spared, so pain and temperature stay normal.

  • D. Spinothalamic and corticospinal tracts

    Spinothalamic loss would remove pain and temperature, and the impaired vibration and position sense would be left unexplained.

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 A, Dorsal columns and corticospinal tracts. Vitamin B12 deficiency causes subacute combined degeneration, a demyelination of the dorsal columns and the lateral corticospinal tracts.

Why is "Anterior horns and spinocerebellar tracts" not the answer?

Anterior horn loss gives wasted, flaccid weakness rather than spasticity, and spinocerebellar damage does not explain loss of vibration sense.

Why is "Dorsal columns and spinothalamic tracts" not the answer?

The dorsal column loss is correct, but spinothalamic fibres are usually spared, so pain and temperature stay normal.

Why is "Spinothalamic and corticospinal tracts" not the answer?

Spinothalamic loss would remove pain and temperature, and the impaired vibration and position sense would be left unexplained.

What concept does this question test?

It tests Neuroanatomy: subacute combined degeneration in Anatomy. The dorsal column loss explains the impaired vibration and position sense, and the corticospinal loss explains the spasticity and extensor plantars. Pain and temperature sensation are usually spared.

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 Neuroanatomy: subacute combined degeneration?

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.