An Unusual Cause of Hypokalemia to Consider

Apparent mineralocorticoid excess syndrome is a rare disorder that can be acquired through inhibition of the enzyme 11 β-hydroxysteroid dehydrogenase type 2 by various substances such as bile acids. We report the case of a 61-year-old woman presenting with painless jaundice. Computed tomography demonstrated a pulmonary as well as a pancreatic tumor, with multiple metastases and dilated bile ducts. Laboratory findings showed persistent hypokalemia despite aggressive enteral and parenteral supplementation, as well as hypertension, metabolic alkalosis, and elevated cholestasis enzymes. Urinary potassium excretion was inappropriately high. Plasma aldosterone concentration was 0.97 ng/dL (26.91 pmol/L) (reference range, 2.21-25.30 ng/dL [61.31-701.82 pmol/L]) and direct renin concentration was 3.9 mIU/L (2.1 ng/L) (reference range, 4.4-46.1 mIU/L [2.53-27.42 ng/L]). Endogenous hypercortisolism was ruled out. After the placement of a metal biliary stent via endoscopic retrograde cholangiopancreatography and the subsequent decrease in cholestasis enzyme levels, potassium levels, hypertension, and metabolic alkalosis gradually normalized. The case was ultimately diagnosed as apparent mineralocorticoid excess syndrome resulting from 11 β-hydroxysteroid dehydrogenase type 2 inhibition caused by elevated bile acids secondary to malignant obstruction of the biliary tract.