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Myotonic dystrophy type 1 (DM1) and type 2 (DM2) are separate genetic diseases with some overlapping and some unique clinical features. Differences between the two diseases in electrical myotonia have been reported but have not been studied systematically. In this study, researchers compared myotonic potential (MP) severity, type, and distribution in 16 patients with genetically confirmed DM1 and 17 patients with genetically confirmed DM2 who underwent prospective, blinded EMG examination.
MPs were elicited more frequently in DM1 (54% of muscle EMG examinations) than in DM2 (41%). In both conditions, MPs were more prominent distally than proximally. However, greater proximal MPs were seen in DM2 than in DM1. The authors did not observe compl…