[Differential diagnostic dilemmas after use of an out-of-date antihypertensive medication. Case report].

Hydrochlorothiazide became one of the most commonly prescribed first-line antihypertensive medication, though its use is often complicated with serious side-effects. A 66-year-old female patient with a history of hypertension had suffered a transient loss of consciousness, and referred to our cardiology unit with an ST-segment elevation and giant negative T-waves in V1-2 ECG leads, long QT-segment and elevated serum creatine-kinase (5392 U/L) and troponin I (4,357 ng/ml) levels. Acute myocardial infarction was not proven (later coronarography revealed preserved coronary circulation), but severe hyponatraemia and hypokalaemia was detected, explaining a possible symptomatic seizure, and which could be accounted for a 25 mg daily hydrochlorothiazide antihypertensive treatment and - as a precipitating insult - a one-week history of gastroenteritis. The case-report presents a unique differential diagnostic question where thiazide-induced hyponatraemia and hypokalaemia resulted in a clinical picture sharing some similarities with acute myocardial infarction. This case underlines the serious side-effects of an inappropriately used common antihypertensive medication. Orv. Hetil., 2017, 158(11), 426-431.