Electrolytes: osmotic demyelination: 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 · Electrolytes: osmotic demyelination

Sample item

A chronic alcohol-dependent woman with serum sodium 108 mmol/L is given hypertonic saline, and sodium rises to 128 mmol/L within 24 hours. Three days later she develops dysarthria, dysphagia and spastic quadriparesis. What is the most likely cause?

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

The answer and the reasoning

A. Osmotic demyelination from overly rapid correction

In chronic hyponatraemia brain cells have lost osmolytes, so a rapid rise in sodium shrinks them and injures oligodendrocytes, mainly in the pons. Features appear 2 to 6 days later. Alcohol use, malnutrition, hypokalaemia and liver disease raise the risk, and correction should not exceed about 8 mmol/L in 24 hours.

Option by option

  • A. Osmotic demyelination from overly rapid correction (correct)

    Correct. A rise of 20 mmol/L in a day, then delayed bulbar and pyramidal signs, is typical of osmotic demyelination.

  • B. Cerebral oedema from persisting hyponatraemia

    Cerebral oedema worsens when sodium falls, and sodium has risen here.

  • C. Wernicke encephalopathy

    Wernicke encephalopathy gives confusion, ophthalmoplegia and ataxia, not delayed spastic quadriparesis.

  • D. Acute inflammatory demyelinating polyneuropathy

    Guillain-Barre syndrome causes flaccid weakness with areflexia, not spasticity and bulbar signs after sodium correction.

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, Osmotic demyelination from overly rapid correction. In chronic hyponatraemia brain cells have lost osmolytes, so a rapid rise in sodium shrinks them and injures oligodendrocytes, mainly in the pons.

Why is "Cerebral oedema from persisting hyponatraemia" not the answer?

Cerebral oedema worsens when sodium falls, and sodium has risen here.

Why is "Wernicke encephalopathy" not the answer?

Wernicke encephalopathy gives confusion, ophthalmoplegia and ataxia, not delayed spastic quadriparesis.

Why is "Acute inflammatory demyelinating polyneuropathy" not the answer?

Guillain-Barre syndrome causes flaccid weakness with areflexia, not spasticity and bulbar signs after sodium correction.

What concept does this question test?

It tests Electrolytes: osmotic demyelination in General Medicine. Features appear 2 to 6 days later. Alcohol use, malnutrition, hypokalaemia and liver disease raise the risk, and correction should not exceed about 8 mmol/L in 24 hours.

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 Electrolytes: osmotic demyelination?

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.