A 20-year-old woman has recurrent muscle cramps and episodes of weakness. Blood pressure is 104/66 mmHg. Labs: potassium 2.6 mEq/L, bicarbonate 30 mEq/L, magnesium 1.1 mg/dL, renin and aldosterone both elevated. Spot urine calcium-to-creatinine ratio is low. Echocardiogram is unremarkable. What is the MOST likely diagnosis?

• A Liddle syndrome due to ENaC gain of function
• B Gitelman syndrome due to SLC12A3 mutation ✓
• C Primary hyperaldosteronism
• D Bartter syndrome type I due to NKCC2 mutation

Explanation

Gitelman syndrome is an autosomal recessive defect of the thiazide-sensitive sodium chloride cotransporter in the distal convoluted tubule, causing salt wasting with hypokalaemic metabolic alkalosis, hypomagnesaemia, hypocalciuria, and normal or low blood pressure with secondary hyperaldosteronism. Liddle syndrome gives the same alkalosis but with hypertension and suppressed renin and aldosterone, which kills that distractor. Bartter mimics loop dysfunction and features hypercalciuria rather than hypocalciuria, often presenting earlier with nephrocalcinosis.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.