Successful treatment with tocainide of recessive generalized congenital myotonia

A patient with recessive generalized congenital myotonia and severe, disabling weakness underwent various forms of treatment while being monitored electrophysiologically. Phenytoin, verapamil, and acetazolamide were ineffective, but tocainide yielded good results. Improvement was dose-dependent, and was limited by irritability and action tremor when the patient was taking 1,600 mg per day.