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Central diabetes insipidus — MCCQE Part 1 MCQ

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HardPolyuria/PolydipsiaCentral diabetes insipidusMCCQE Part 1

A 38-year-old man has polyuria, polydipsia, nocturia. Random glucose 4.5 mmol/L. Na 150, serum osmolality 305, urine osmolality 120. After DDAVP, urine osmolality rises to 600. Most likely diagnosis?

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Correct answer: A — Central diabetes insipidus

Hypernatraemia + high serum osmolality + dilute urine = DI. Response to DDAVP (urine osmolality >600) = central DI. Nephrogenic DI: no response to DDAVP. MRI pituitary indicated.

Reference: Endocrine Society / Canadian guidelines