82-year-old woman with a history of breast neoplasia treated with surgery and hormone therapy 20 years ago, hypertensive cardiomyopathy in sinus rhythm, hypercholesterolemia and moderate chronic hyponatremia around 133 mmol/L. He was treated with torasemide 5 mg/24h, isosorbide mononitrate 50 mg/24h, acetylsalicylic acid 100 mg/24h, pravastatin 20 mg/24h, candesartan 32 mg/24h, hydrochlorothiazide 12.5 mg/24h, atenolol 50 mg/24h and spironolactone 25 mg/24h.
She started treatment with sertraline 50 mg/24h, with her usual natraemia figures, for suspected depressive syndrome, six weeks before admission. After two weeks, his general condition worsened, with nausea, vomiting, needing help with daily activities and behavioural alterations. One month later, hyponatraemia of 119 mmol/L was detected, sertraline was discontinued and water restriction was started at home for three days, with no improvement in symptoms. She was admitted to Internal Medicine with a diagnosis of confusional syndrome secondary to urinary tract infection and/or hyponatraemia.
A diagnosis of hyponatraemia was made, probably secondary to sertraline. Laboratory tests on admission were compatible with SIADH. Thyroid hormone values (TSH: 4.04 mIU/L, free T4: 1.72 ng/dL, free T3: 3.13 pg/mL) and cortisol (19.7 μg/dL) were within the normal range. Hyponatraemia was treated on the first day with discontinuation of sertraline, torasemide, hydrochlorothiazide and spironolactone, oral water restriction, fluid therapy (1500 mL NaCl 0.9%/24h i.v.) and furosemide 20 mg/12h i.v. with initial improvement of natraemia. The rest of the home treatment was maintained during admission.
Treatment was continued for 4 days with water restriction to less than 500 mL daily, improving natraemia to 132 mmol/L, but two days later it decreased again, which led to the use of tolvaptan 15 mg/24h vo for two days and 30 mg one more day, which restored natraemia and led to hospital discharge. It was confirmed that natraemia was maintained acceptably in subsequent controls after hospital discharge.
Treatment at discharge was losartan 100 mg/24h, atenolol 50 mg/12h, trazodone 50 mg/24h, pravastatin 10 mg/24h, alendronic acid 70 mg/7 days, calcium carbonate/cholecalciferol 1250 mg/400 IU/24h and low sodium diet.

