[The Gitelman syndrome--a differential diagnosis of Bartter syndrome].

BACKGROUND

Hypokalemia due to renal potassium wasting in the absence of hypertension, moderate metabolic alkalosis, hyperreninism and hyperaldosteronism suggest the presence of Bartter's syndrome. The underlying cause is an inherited defect of sodium chloride reabsorption in the thick ascending limb of Henle. A differential diagnosis of Bartter's syndrome is Gitelman's syndrome, another hypokalemia-hypomagnesemia syndrome, which is thought to be caused by a transport defect in the distal tube.

PATIENTS AND METHODS

We report 3 patients presenting with signs primarily suggestive of Bartter's syndrome, who turned out to have Gitelman's syndrome after determining the excretion of calcium in the urine.

RESULTS

Two women, 36- and 55-year old, suffered from paresthesias in the hands and feet and from tetanic convulsions. The brother of the 36-year old woman presented in our hospital because of an accidentally discovered hypokalemia without any clinical symptoms. In all patients the outstanding biochemical features were hypokalemia, hypomagnesemia and moderate metabolic alcalosis. The renin and aldosterone values were inappropriately high. The most characteristic finding in the urine, besides the presence of hyperkaliuria was the diminution of calcium excretion, despite normocalcemia.

CONCLUSION

The association between sodium and calcium reabsorption in the loop of Henle predicts hypercalciuria in patients with a defect in salt reabsorption in this segment, as in Bartter's syndrome. In Gitelman's syndrome the laboratory features resemble the findings in Bartter's syndrome, except for the presence of hypocalciuria. Since hypocalciuria follows also the administration of thiazide diuretics, which act in the early part of distal tube, a transport defect in this part of the tube is thought to be responsible for the electrolyte disturbances in Gitelman's syndrome. The measurement of the urinary calcium excretion in patients with an unclear hypokalemia-hypomagnesemia-syndrome allows easily the differentiation between Bartter's and Gitelman's syndrome.