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SSRI-induced SIADH — SCE Acute Medicine MCQ

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HardMedicine in the elderlySSRI-induced SIADHSCE Acute Medicine

A 70-year-old woman is admitted after a fall and new confusion. She is afebrile, pain-free and has no focal neurology. Sodium is 118 mmol/L, serum osmolality 255 mOsm/kg, urine osmolality 540 mOsm/kg and urine sodium 52 mmol/L. She started sertraline three weeks ago. What is the most likely underlying cause?

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Correct answer: A — Syndrome of inappropriate antidiuresis triggered by sertraline

The low serum osmolality with inappropriately concentrated urine and high urine sodium is typical of SIADH. SSRIs are common precipitants in older adults and can present with falls or delirium rather than seizures. Primary polydipsia would have dilute urine, while hypovolaemia usually has low urine sodium unless diuretics are confounding.

Reference: NICE CKS Hyponatraemia; Society for Endocrinology Emergency Guidance