Electrolytes: cerebral salt wasting: 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 · Electrolytes: cerebral salt wasting

Sample item

On day 5 after a subarachnoid haemorrhage, a 50-year-old man has serum sodium 122 mmol/L. He has dry mucous membranes, postural hypotension and a low central venous pressure. Urine sodium is 70 mmol/L and urine osmolality is 480 mOsm/kg. What is the most appropriate management?

ADemeclocyclineBIsotonic saline volume replacement, with fludrocortisone if neededCTolvaptanDStrict fluid restriction

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

The answer and the reasoning

B. Isotonic saline volume replacement, with fludrocortisone if needed

Cerebral salt wasting after intracranial disease causes renal sodium loss and true volume depletion, which resembles SIADH biochemically (high urine sodium and osmolality) but differs in volume status. Treatment is to replace sodium and volume with isotonic or hypertonic saline, and fludrocortisone can help. Fluid restriction would worsen hypovolaemia and increase the risk of vasospasm and cerebral infarction after subarachnoid haemorrhage.

Option by option

A. Demeclocycline
Demeclocycline induces nephrogenic diabetes insipidus for chronic SIADH and would aggravate volume loss.
B. Isotonic saline volume replacement, with fludrocortisone if needed (correct)
Correct. The patient is hypovolaemic and salt-depleted, so volume and sodium replacement is needed.
C. Tolvaptan
Tolvaptan, a vasopressin antagonist, promotes water loss and would worsen hypovolaemia.
D. Strict fluid restriction
Fluid restriction suits euvolaemic SIADH and here would worsen volume depletion and delayed cerebral ischaemia.

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, Isotonic saline volume replacement, with fludrocortisone if needed. Cerebral salt wasting after intracranial disease causes renal sodium loss and true volume depletion, which resembles SIADH biochemically (high urine sodium and osmolality) but differs in volume status.

Why is "Demeclocycline" not the answer?

Demeclocycline induces nephrogenic diabetes insipidus for chronic SIADH and would aggravate volume loss.

Why is "Tolvaptan" not the answer?

Tolvaptan, a vasopressin antagonist, promotes water loss and would worsen hypovolaemia.

Why is "Strict fluid restriction" not the answer?

Fluid restriction suits euvolaemic SIADH and here would worsen volume depletion and delayed cerebral ischaemia.

What concept does this question test?

It tests Electrolytes: cerebral salt wasting in General Medicine. Treatment is to replace sodium and volume with isotonic or hypertonic saline, and fludrocortisone can help. Fluid restriction would worsen hypovolaemia and increase the risk of vasospasm and cerebral infarction after subarachnoid haemorrhage.

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 Electrolytes: cerebral salt wasting?

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.