Neurology: narcolepsy mechanism: 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.

Try it

General Medicine · Neurology: narcolepsy mechanism

Sample item

A 19-year-old has excessive daytime sleepiness with irresistible sleep attacks, sudden loss of muscle tone on laughing, and vivid hallucinations on falling asleep. Which neurochemical abnormality underlies this condition?

ALoss of cholinergic neurones in the nucleus basalisBLoss of hypothalamic neurones that produce orexinCExcess GABA release from the reticular formationDDegeneration of dopaminergic neurones in the substantia nigra

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

The answer and the reasoning

B. Loss of hypothalamic neurones that produce orexin

Narcolepsy type 1 results from loss of lateral hypothalamic neurones producing orexin (hypocretin), which stabilises wakefulness. This allows REM features such as cataplexy and hypnagogic hallucinations to intrude. CSF orexin is low.

Option by option

A. Loss of cholinergic neurones in the nucleus basalis
Basal forebrain cholinergic loss is associated with Alzheimer disease.
B. Loss of hypothalamic neurones that produce orexin (correct)
Correct. Loss of orexin neurones causes cataplexy, sleep attacks and hypnagogic hallucinations.
C. Excess GABA release from the reticular formation
Excess GABA is not the mechanism of narcolepsy.
D. Degeneration of dopaminergic neurones in the substantia nigra
Nigral dopaminergic loss causes Parkinson disease.

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.

Questions about this General Medicine question

What is the answer to this General Medicine question?

The best answer is B, Loss of hypothalamic neurones that produce orexin. Narcolepsy type 1 results from loss of lateral hypothalamic neurones producing orexin (hypocretin), which stabilises wakefulness.

Why is "Loss of cholinergic neurones in the nucleus basalis" not the answer?

Basal forebrain cholinergic loss is associated with Alzheimer disease.

Why is "Excess GABA release from the reticular formation" not the answer?

Excess GABA is not the mechanism of narcolepsy.

Why is "Degeneration of dopaminergic neurones in the substantia nigra" not the answer?

Nigral dopaminergic loss causes Parkinson disease.

What concept does this question test?

It tests Neurology: narcolepsy mechanism in General Medicine. This allows REM features such as cataplexy and hypnagogic hallucinations to intrude. CSF orexin is low.

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 Neurology: narcolepsy mechanism?

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.