Psychotic disorders: psychogenic polydipsia: practice question

A Psychiatry 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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Psychiatry · Psychotic disorders: psychogenic polydipsia

Sample item

A 40-year-old man with chronic schizophrenia drinks about 8 litres of water daily. He is brought with confusion and a generalised seizure. Serum sodium is 118 mmol/L and the urine is very dilute. What is the most likely cause?

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

The answer and the reasoning

A. Primary polydipsia causing water intoxication

Compulsive water drinking in chronic psychosis overwhelms renal excretion and dilutes the serum sodium, while the kidney correctly makes dilute urine. Diabetes insipidus produces high sodium because water is lost, and SIADH gives concentrated urine.

Option by option

  • A. Primary polydipsia causing water intoxication (correct)

    Correct. Excess intake with appropriately dilute urine and low sodium points to primary polydipsia.

  • B. Syndrome of inappropriate antidiuretic hormone secretion

    SIADH produces inappropriately concentrated urine, not very dilute urine.

  • C. Lithium-induced nephrogenic diabetes insipidus

    Nephrogenic diabetes insipidus also causes water loss with a high or normal sodium, and the stem names no lithium.

  • D. Central diabetes insipidus

    Central diabetes insipidus loses water, so serum sodium rises rather than falls.

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 Psychiatry question

What is the answer to this Psychiatry question?

The best answer is A, Primary polydipsia causing water intoxication. Compulsive water drinking in chronic psychosis overwhelms renal excretion and dilutes the serum sodium, while the kidney correctly makes dilute urine.

Why is "Syndrome of inappropriate antidiuretic hormone secretion" not the answer?

SIADH produces inappropriately concentrated urine, not very dilute urine.

Why is "Lithium-induced nephrogenic diabetes insipidus" not the answer?

Nephrogenic diabetes insipidus also causes water loss with a high or normal sodium, and the stem names no lithium.

Why is "Central diabetes insipidus" not the answer?

Central diabetes insipidus loses water, so serum sodium rises rather than falls.

What concept does this question test?

It tests Psychotic disorders: psychogenic polydipsia in Psychiatry. Diabetes insipidus produces high sodium because water is lost, and SIADH gives concentrated urine.

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 Psychotic disorders: psychogenic polydipsia?

Learn each diagnosis by its core features and its first-line treatment. Then use the flashcards and the other Psychiatry 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.