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Post-Surgical Central DI — RACP Adult Medicine MCQ

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ModerateEndocrinologyPost-Surgical Central DIRACP Adult Medicine

A 35-year-old man post-transsphenoidal pituitary surgery develops polyuria (8 L/day) and polydipsia 24 hours post-operatively. Na⁺ is 152 mmol/L. Urine osmolality is 120 mOsm/kg (dilute). Serum osmolality is 310 mOsm/kg. After DDAVP administration, urine osmolality rises to 650 mOsm/kg. What is the most likely cause?

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Correct answer: A — Central diabetes insipidus

Post-pituitary surgery with polyuria, hypernatraemia, dilute urine (inappropriately low osmolality for serum hypertonicity), and response to DDAVP (urine concentrates) is central diabetes insipidus. ADH deficiency from surgical damage to the posterior pituitary or stalk. Post-surgical CDI may be transient (days-weeks) or permanent. Treatment: DDAVP (desmopressin) intranasal or oral. Monitor for triphasic response (CDI → SIADH → CDI).

Reference: eTG Endocrine – 2024 – DI; Endocrine Society 2023