[Clinical reasoning and decision-making in practice. A woman with hypokalaemia].

A 39-year-old woman had been investigated elsewhere due to symptomatic hypokalaemia, renal potassium wasting and metabolic alkalosis. Vomiting was considered to be the underlying cause but the patient repeatedly denied this behaviour. After extensive investigations, Bartter's syndrome was finally diagnosed. Eighteen months later the patient was readmitted due to progressive renal insufficiency. On the basis of a very low urinary chloride excretion and the aforementioned laboratory results, it was concluded that the metabolic disturbances were due to vomiting and the diagnosis of Bartter's syndrome was rejected. Upon being confronted with these findings, the patient finally admitted to vomiting, but stated that this happened involuntarily after meals. She had a stenotic ulcer in the pylorus and a gastric biopsy demonstrated the presence of Helicobacter pylori associated gastritis. Eradication therapy was given and the symptoms disappeared. The renal insufficiency was partly accounted for by hypovolaemia and partly by tubulointerstitial nephropathy (demonstrated by kidney biopsy) which was probably due to the chronic hypokalaemia. This case illustrates the difficulty of establishing the differential diagnosis of hypokalaemia, especially in the case of denied vomiting. However, it also shows that in such cases the correct diagnosis can be made if objective parameters are used.