Background Hypokalaemia (HK) is found in up to 20% of people with eating disorders and is a clinically relevant electrolyte abnormality, since it can cause life-threatening conditions, such as cardiac arrhythmias, myopathy, rhabdomyolysis, and nephropathy. HK in eating disorders usually develops as a result of diuretic improper use and gastrointestinal losses.

This report describes a teen girl with a severe HK. A thorough medical history and proper laboratory tests allowed an early and accurate diagnosis and treatment.

Clinical case A 15-year-old female patient was admitted to our emergency department with a four month history of weakness, dizziness, light-headedness, nausea and abdominal pain, and mild myalgia. On admission, she was fully responsive. Physical examination was unremarkable, blood pressure was 115/78 mmHg, heart rate 81 bpm. Blood tests revealed severe HK (1.9 mmol/L), hyponatremia (125 mmol/L), hypochloraemia (77 mmol/L), hypomagnesaemia (0.68 mmol/L), metabolic alkalosis (HCO₃^-28.2 mmol/L) and pre-renal acute kidney insufficiency (creatinine 71µmol/l). ECG showed severe abnormalities of ventricular repolarization (QTc max 0.52 msec).

Intravenous K⁺ supplementation, together with rehydration was immediately undertaken. Over the following 48–72 hours, electrolytes, metabolic alkalosis, kidney insufficiency and the ECG intervals gradually normalised.

The adolescent denied diarrhoea, vomiting, and any ingestion of laxatives, and diuretics. Nevertheless, finally urine screening for diuretics showed a large amount of furosemide. On ultrasound scan signs of mild nephrocalcinosis were found as well, indicating chronic abuse of diuretics.

When faced with the positive result of diuretic intake, the patient finally admitted the drug abuse and self-dietary restrictions over the last months. The patient agreed to stop taking diuretics and to undergo a psychiatric evaluation.

Conclusions HK is the most relevant electrolyte abnormality in patients with eating disorders. Only a minority of adolescents with eating disorders abuse diuretics and correct and prompt diagnosis can be very difficult, as these patients often deny diuretic intake.

Concealed diuretic abuse, associated or not with surreptitious vomiting and laxative abuse, should always be taken into account in young women with eating disorders.

Urine screening for diuretics should be performed in patients who deny diuretic intake.