MYOTONIA

muscular disorder involving difficulty in relaxing voluntary muscles after contraction. All the bodily muscles or only a few may be affected. The cause of the disorder is unknown, but it seems to be a difficulty inherent in the muscles themselves and not in the nervous system (myopathy). One rather rare form of the disorder, thought to be inherited in most instances, is known as myotonia congenita, or Thomsen's disease. The disease is first noticed in early childhood. The eyelids and eyes can be affected; the eyes appear to be stuck in one position, and the lids remain closed after forceful shutting. There may also be difficulty in swallowing or in talking owing to prolonged contraction of the throat muscles. A quick movement causes muscle stiffening. The muscles show no weakness when used, and the fibres are usually more developed than in the normal person. There is some suggestion that this overdevelopment is caused by involuntary and repeated isometric exercise during attempts to make the muscle react normally or that there might be some replacement of the tissue with fat and fibrous scar tissue. Some cases of muscular dystrophy, in which there is usually a gradual weakening of the muscles, also show stages of myotonia. This form is also inherited, but it does not become apparent until the third or fourth decade; the muscles do not overdevelop but gradually degenerate. The stiffening effect of the myotonia may precede the degeneration by two to three years. Most instances of myotonia can be distinguished from muscular dystrophy because the myotonia fails to show the dystrophy symptoms of weakness, cataracts, baldness, and gonadal atrophy. Symptoms of myotonia can be alleviated by administration of analgesics, anesthetics, and anticonvulsant drugs.