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Postoperative SIAD — SCE Endocrinology MCQ

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HardPituitaryPostoperative SIADSCE Endocrinology

A 44-year-old woman has persistent hyponatraemia after pituitary surgery. Sodium is 122 mmol/L, serum osmolality 260 mOsm/kg, urine osmolality 620 mOsm/kg and urine sodium 78 mmol/L. She is euvolaemic and cortisol replacement is adequate. What is the most likely diagnosis?

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Correct answer: C — Syndrome of inappropriate antidiuresis after pituitary surgery

Euvolaemic hypotonic hyponatraemia with inappropriately concentrated urine and high urine sodium after pituitary surgery supports SIAD. Diabetes insipidus causes hypernatraemia with dilute urine. The pearl is that pituitary surgery can produce a triphasic water-balance pattern.

Reference: Society for Endocrinology guidance on pituitary surgery water balance