Diagnosis and clinical approach in Gitelman's syndrome

Hypokalemia, defined as a plasma potassium concentration <3.5 mmol/l, is the most common electrolyte abnormality encountered in our clinical practice. Unfortunately, in many cases, the etiologies were unclear and resulted in a wrong treatment. Indeed, the true etiology could be such a 'rare' one and could be found by doing a comprehensive work up. One of this is Gitelman's syndrome, a rare genetic disorder characterized by hypokalemic alkalosis, hypomagnesemia, hypocalciuria, and secondary aldosteronism without hypertension. Since this disorder is found in 1% Caucasian populations, this is one of the most frequently inherited renal tubular disorders. A 27 year old man came to emergency room with weakness and generalised muscle cramps. He was investigated three months before for a similar electrolyte disturbance which was found to be inconclusive. The routine laboratory data in emergency room revealed a potassium concentration of 2.3 mmol/l. He had never used diuretics or hormonal therapy nor had history of vomiting or diarrhea. He had normal blood pressure and the blood gas analysis revealed metabolic alkalosis. On his ECG (electrocardiography), we found the prominent U wave. Despite his low concentration of serum potassium and cloride, the concentration of these electrolytes in urine were extremely high. We also found hipomagnesemia. The calcium concentration in serum was normal with slightly hypocalciuria. Even with aggressive oral and intravenous potassium suplementation, the patient remained hypokalemic. In cases when the etiology of hypokalemia is unclear, we should perform some investigations to confirm the diagnosis and give the proper treatment. In Gitelman's syndrome, where the defect in the distal tubule cannot be corrected, the treatment must be a life-long. Most patients require oral potassium and magnesium supplementation, since drug therapy is usually incompletely effective.