Mexiletine for Nondystrophic Myotonia

The nondystrophic myotonias (NDMs) are a group of rare disorders (prevalence 1:100,000) of skeletal muscle excitability, caused by mutations in skeletal muscle chloride and sodium channels. Stiffness is the most common and most severe symptom of the NDMs, which may also cause muscle pain, fatigue, and weakness. To date, treatment for this group of disorders has been largely anecdotal. Now, researchers from the Consortium for Clinical Investigation of Neurologic Channelopathies (CINCH) have examined the safety and efficacy of mexiletine, a class 1b antiarrhythmic drug that has high affinity for muscle sodium channels. In this randomized, double blind, placebo-controlled, crossover trial, the researchers randomized 59 patients with NDM to rec…