An 82-year-old woman becomes confused and unsteady over three days while being treated for depression and hypertension. She is euvolaemic, her serum sodium is 124 mmol/L (reference range 135–145), serum osmolality is 258 mOsm/kg (reference range 275–295), urine osmolality is 480 mOsm/kg (reference range less than 100 when plasma is hypo-osmolar) and urine sodium is 62 mmol/L (reference range variable). Thyroid function and an 08:00 serum cortisol are normal, and she is not taking a diuretic. Which one of the following is the most likely cause?
Keep going — a set of ten like this one, one at a time.
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