Electrophysiological analysis of warming up phenomenon in myotonia.

The after discharges following grip and percussion in myotonia of 4 cases with myotonic dystrophy were evaluated in repetitive percussion or grip, in cold exposure and in warm exposure electromyographically. By repetition, the after discharges reduced markedly. After 2 or 3 trials, after discharges disappeared or became short duration. During local cooling (15 degrees C-20 degrees C), the amplitude and the prolongation in the duration of after discharges were marked, although these enhanced after discharges were reduced by repetition even in cooling. During local warming (40 degrees C-42 degrees C), the after discharges became less marked or disappeared. Both the warming of muscle and the repetitive movements reduced the duration of abnormal after discharges. These effect might be explained on the same mechanism which was the change of the ion transport in muscle membrane, and could be called as warming up phenomenon together. The degree of these after discharges are close related to the degree of myotonic phenomenon. Myotonia is the disorder of primarily the electrical excitabilities, not the contractile properties. So the method of evaluation of after discharges electromyographically is very valuable compared to the measurement of the relaxation process which was used popular in evaluation of myotonia in the past.