a hereditary neuromuscular disease in which a contracted muscle is unable to relax for a long time; muscular relaxation proceeds very slowly. Depending on the clinical course of the disease, congenital, atrophic, cold, and paradoxical forms of myotonia are distinguished. The disease may occur in several members of a family; males are more often affected. There are no marked morphological changes in the nervous system or the muscles. There may be dysfunctions of the autonomic nervous system and the endocrine glands. Increased sensitivity to acetylcholine and potassium are characteristic of the disease. The principal sign of myotonia is impaired myofibril contractility, that is, relaxation of contracted muscles is greatly impaired. The muscles are firm to the touch. Myotonia progresses slowly, with general deterioration frequently setting in after overexposure to low temperatures, mental stress, and excessive fatigue. Treatment includes hormone therapy, vitamin therapy, and physical therapy.