Myotonia in ion channel diseases of muscle.

Ion channel dysfunctions of the muscular cell membrane are usually inheritable, rare diseases. They may become manifest as relatively mild symptoms of muscle stiffness and pain, myotonia or paralysis. We describe two young patients who had an inherited ion channel disease of the muscular cell membrane with mild symptoms. The first patient had a chloride channel dysfunction of the muscular cell membrane, the second one a sodium channel dysfunction. In electromyography findings typical of the respective ion channel disease were detected in both patients. Closer examination of the patients' myotonic sequences occurring in electromyography of the relaxed muscle revealed differences that already enable the evaluation of the type of ion channel disease.