A 20-year-old woman has recurrent episodes of carpopedal spasm. Labs: K 2.7, Mg 1.1 mEq/L, HCO3 32 mEq/L, arterial pH 7.50, normal blood pressure, urine calcium-to-creatinine ratio markedly low. The most likely diagnosis is:
- A Bartter syndrome
- B Gitelman syndrome ✓
- C Primary hyperaldosteronism
- D Liddle syndrome
Correct answer: B. Gitelman syndrome
Explanation
Gitelman syndrome results from mutations in the thiazide-sensitive Na-Cl cotransporter in the distal convoluted tubule, producing hypokalemic metabolic alkalosis with hypomagnesemia and characteristically LOW urinary calcium. Bartter syndrome mimics a loop-diuretic effect and gives hypercalciuria, which is the key discriminator. Both hyperaldosteronism and Liddle syndrome cause hypertension, which is absent here.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
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