Therapy of myotonia;

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Abstract
In a randomized, double-blind and crossover study diphenylhydantoin was as effective as procainamide in relieving myotonia, subjectively and objectively. Diphenylhydantoin was better tolerated than procainamide. Diphenylhydantoin did not increase preexisting cardiac conductive defects while procainamide did so in 3 of 5 patients. Myotonia may be due to an unstable muscle fiber membrane. Diphenylhydantoin may provide stabilization of the myotonic muscle membrane by inducing a favorable decrease in intracellular Na.