A 40-year-old woman has a serum potassium of 2.8 mEq/L, normal blood pressure, and urinary potassium excretion of 60 mEq/day (raised). Serum bicarbonate is 30 mEq/L. Blood gas shows metabolic alkalosis. Serum aldosterone and renin are BOTH suppressed. Which is the MOST likely diagnosis?

• A Primary hyperaldosteronism
• B Gitelman syndrome
• C Liddle syndrome ✓
• D Apparent mineralocorticoid excess (AME)

Explanation

Liddle syndrome is a gain-of-function mutation in ENaC (epithelial sodium channel) causing sodium retention, hypokalaemia, metabolic alkalosis, and hypertension with SUPPRESSED renin and aldosterone — differentiating it from primary hyperaldosteronism where aldosterone is elevated. This is the key diagnostic clue. AME (11β-HSD2 deficiency) presents similarly but is caused by cortisol acting on mineralocorticoid receptors; urine cortisol-to-cortisone ratio is elevated. Gitelman syndrome presents with low BP, low magnesium, and normal/elevated renin. Liddle syndrome responds to amiloride/triamterene (ENaC blockers), not spironolactone.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.