Toe-extension myotonia in myotonic dystrophy type 1.

Abstract

Myotonia is a cardinal symptom of adult-onset myotonic dystrophy type 1 (DM1). Myotonia, delayed relaxation following contraction, is most prominent in the hand and forearm muscles. Two sisters with genetically confirmed DM1 exhibited toe-extension myotonia (video on the Neurology® Web site at [Neurology.org][1]) in contrast to toe-flexion myotonia that can occur in DM1. There was a typical warm-up phenomenon. A variant phenotype of Charcot-Marie-Tooth–like polyneuropathy1 was not present. Mutations in the CLCN1 gene encoding the skeletal muscle chloride channel, in addition to abnormal splicing, can enhance myotonia in DM type 2.2 However, in our patients sequencing of the CLCN1 gene did not show mutations. Acknowledgment: The authors thank Drs. Thornton and Moxley (University of Rochester, NY) for discussions; and Hirity Shimellis, Angela Kokkinis, and Dara Bakar for help with patient care and making of the video. [1]: http://neurology.org/lookup/doi/10.1212/WNL.0000000000001734