A 21-year-old woman is evaluated for recurrent muscle cramps and an episode of tetany. BP 108/68 mmHg. Serum potassium 2.6 mEq/L, magnesium 1.2 mg/dL, chloride 114 mEq/L, bicarbonate 31 mEq/L, calcium 9.0 mg/dL. Twenty-four hour urine calcium excretion is markedly low. Plasma renin and aldosterone are mildly elevated. What is the diagnosis?

• A Gitelman syndrome ✓
• B Bartter syndrome type III
• C Primary hyperaldosteronism
• D Liddle syndrome

Explanation

Gitelman syndrome is an inherited defect of the distal convoluted tubule thiazide-sensitive NaCl cotransporter, producing a phenocopy of chronic thiazide use: hypokalaemic metabolic alkalosis, hypomagnesaemia causing tetany, and characteristically HYPOcalciuria, with normal or low blood pressure. The single fact that separates it from Bartter syndrome is the urine calcium: Bartter mimics the loop of Henle defect and gives HYPERcalciuria with onset in infancy. Primary hyperaldosteronism and Liddle syndrome cause hypertension, absent here.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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