Distribution of electrical myotonia in myotonic muscular dystrophy

Twenty-five successive patients with myotonic dystrophy were examined to determine the anatomical distribution of electrical myotonia. Proximal and distal limb muscles and orbicularis oris and masseter muscles were examined. Electrical myotonia was present in all muscles examined in only 3 patients. Moreover, of the 15 muscles examined, none showed myotonic discharges in every patient, the highest individual muscle involvement being 96%.