Hypokalemic weakness in hyperaldosteronism: activity-dependent conduction block.

The authors describe a 48-year-old man who presented with acute weakness. Serum K+ was 1.7 mmol/L, and investigations established hyperaldosteronism. Nerve excitability studies during hypokalemia demonstrated that axons were of high threshold with a fanning out of threshold electrotonus, consistent with hyperpolarization. Activity-dependent conduction block was induced by voluntary contraction. Excitability abnormalities resolved with K+ replacement. Activity-dependent conduction block induced by normal activity may contribute to weakness and paralysis developing with hypokalemia.