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Central diabetes insipidus — SCE Endocrinology MCQ

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HardPituitaryCentral diabetes insipidusSCE Endocrinology

A 41-year-old man passes 7 litres of urine daily after transsphenoidal surgery. Serum sodium is 151 mmol/L, plasma osmolality 306 mOsm/kg and urine osmolality 92 mOsm/kg. After desmopressin, urine osmolality rises to 510 mOsm/kg. What is the most likely diagnosis?

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Correct answer: ECentral diabetes insipidus

Hypernatraemia with dilute urine indicates water diuresis, and a strong response to desmopressin confirms central arginine vasopressin deficiency. Nephrogenic diabetes insipidus would show little response to desmopressin. The pearl is that postoperative pituitary water balance can change rapidly and needs close sodium monitoring.

Reference: Society for Endocrinology guidance on arginine vasopressin deficiency