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Drug-Induced SIADH — ESENeph MCQ

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EasyElectrolyte DisordersDrug-Induced SIADHESENeph

A 30-year-old woman with epilepsy on Carbamazepine presents with serum sodium of 126 mmol/L. She is euvolaemic. Urine osmolality is 350 mOsm/kg and urine sodium is 40 mmol/L. TSH and cortisol are normal. What is the cause?

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Correct answer: D — Drug-induced SIADH from Carbamazepine

Carbamazepine is a well-known cause of SIADH (syndrome of inappropriate ADH secretion). It enhances the effect of ADH on the collecting duct. The biochemical picture confirms SIADH: hyponatraemia with euvolaemia, concentrated urine (>100 mOsm/kg), and elevated urine sodium (>30 mmol/L) with normal thyroid/adrenal function. Management involves switching anticonvulsant if possible, fluid restriction, and monitoring sodium. Other drug causes include SSRIs, Cyclophosphamide, and Oxcarbazepine.

Reference: Spasovski et al 2014 – Hyponatraemia Guideline; BNF 2024 – Carbamazepine ADRs