Severe muscle weakness due to hypokalemia as a manifestation of small-cellcarcinoma

We describe the case of a 56-year-old man with severe muscle weakness due t o heavy hypokalemia (serum potassium 1.44 mmol/l) associated with inappropr iate kaliuria and alkalemia, Subsequent investigation revealed the presence of ectopic ACTH hypersecretion due to a small-cell lung carcinoma, A signi ficant clinical/laboratory improvement was achieved following chemotherapy- induced regression of the primary tumor. The profound hypokalemia was proba bly the result of cortisol hypersecretion, which in concert with the ACTH-i nduced decreased 11 beta-hydroxysteroid dehydrogenase activity can exhibit an increased mineralocorticoid activity. In addition, other ACTH-dependent mineralocorticoids may play a contributory role in the development of sever e hypokalemia.