Neurology: internuclear ophthalmoplegia: practice question

A General Medicine 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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General Medicine · Neurology: internuclear ophthalmoplegia

Sample item

A 28-year-old woman with relapsing neurological episodes cannot adduct her right eye on looking to the left, while the left eye abducts with nystagmus. Convergence is preserved. Which structure is damaged?

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

The answer and the reasoning

A. Right medial longitudinal fasciculus

Internuclear ophthalmoplegia is named by the side of failed adduction and results from a lesion of the medial longitudinal fasciculus on that side. The abducting eye shows nystagmus, and convergence is spared because the medial rectus subnucleus and nerve are intact. In young adults the usual cause is multiple sclerosis.

Option by option

  • A. Right medial longitudinal fasciculus (correct)

    Correct. The right MLF carries the signal for right medial rectus adduction during left gaze.

  • B. Left medial longitudinal fasciculus

    A left MLF lesion causes failure of left eye adduction on right gaze.

  • C. Right oculomotor nerve

    A third nerve palsy would impair convergence and usually cause ptosis and a dilated pupil.

  • D. Right abducens nucleus

    An abducens nucleus lesion causes a horizontal gaze palsy and not isolated failure of adduction.

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.

More General Medicine questions

Questions about this General Medicine question

What is the answer to this General Medicine question?

The best answer is A, Right medial longitudinal fasciculus. Internuclear ophthalmoplegia is named by the side of failed adduction and results from a lesion of the medial longitudinal fasciculus on that side.

Why is "Left medial longitudinal fasciculus" not the answer?

A left MLF lesion causes failure of left eye adduction on right gaze.

Why is "Right oculomotor nerve" not the answer?

A third nerve palsy would impair convergence and usually cause ptosis and a dilated pupil.

Why is "Right abducens nucleus" not the answer?

An abducens nucleus lesion causes a horizontal gaze palsy and not isolated failure of adduction.

What concept does this question test?

It tests Neurology: internuclear ophthalmoplegia in General Medicine. The abducting eye shows nystagmus, and convergence is spared because the medial rectus subnucleus and nerve are intact. In young adults the usual cause is multiple sclerosis.

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 Neurology: internuclear ophthalmoplegia?

For each disease know the classic presentation, the best test, and the first-line treatment. Then use the flashcards and the other General Medicine 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.