Hypokalaemia tetraparesis and rhabdomyolysis: aetiology discovered on a normal lung radiograph

A 21-year-old woman was referred to our unit to elucidate the aetiology of three episodes of hypokalaemic tetraparesis that had occurred over the last 8 years. The third episode had led to emergency hospitalization for severe rhabdomyolysis (creatine phosphokinase level up to 20 000 IU/l) associated with life-threatening hypokalaemia (1.21mmol/l). On her island, the tertiary care facility in which she had been admitted had simply performed measurements of serum electrolytes and had not been impressed by bicarbonate levels of 16mmol/l that had been attributed to diarrhoea. This was unlikely, however, as the urinary potassium level was 29mmol per 24 h. She had rapidly recovered with intravenous potassium infusions. She had no salient personal or family history. She had never passed urinary stones. She denied intake of any drug and had a strong dislike of liquorice. When questioned, she remembered that the three episodes of tetraparesis had occurred after a bout of diarrhoea. On arrival at our hospital she looked healthy. Her blood pressure was 115/60mmHg and her body weight was 45 kg. Muscular strength and reflexes were normal. Serum creatinine was 97 mmol/l and creatinine clearance derived from the Cockcroft and Gault equation was 67ml/min/1.73m. Serum electrolytes were (mmol/l): Na, 141; K, 2.9; Cl, 113; HCO 3 , 17; Ca, 2.10; and PO4 1.1. Serum albumin level was 39 g/l. Urinary potassium was 50mmol per 24 h. The diagnostic work-up included a chest radiograph. The lungs were normal. However, the diagnosis was made on this film, which is shown in Figure 1.