Syndrome of inappropriate antidiuretic hormone secretion (SIADH) and enalapril

A 69-year-old woman with a history of diabetes and hypertension, was referred to the Hospital of Laredo because of hyponatraemia. She had weakness and slight dyspnoea with no evidence of extracellular fluid volume depletion or oedema. Serum sodium level on admission was 125 mol l-1, plasma osmolality 270 mosmol kg-1, simultaneous urine osmolality was 580 mosmol kg-1 and urine sodium 32.6 mmol l-1. She had been treated with enalapril (20 mg) daily for 4 months. She was diagnosed with the Syndrome of inappropriate secretion of antidiuretic hormone (SIADH) that was reversed after cessation of treatment with enalapril and reappeared on reintroduction of the drug at the same daily doses.