Myotonia congenita is an inherited neuromuscular disorder characterized by the inability of muscles to quickly relax after a voluntary contraction. The condition is present from early childhood, but symptoms can be mild. Most children will be 2 or 3 years old when parents first notice their muscle stiffness, particularly in the legs, often provoked by sudden activity after rest. The disease doesn’t cause muscle wasting; in fact, it may cause muscle enlargement. Muscle strength is increased. There are two forms of the disorder: Becker-type, which is the most common form; and Thomsen’s disease, which is a rare and milder form. The disorder is caused by mutations in a gene responsible for shutting off electrical excitation in the muscles.
Most people with myotonia congenita don’t require special treatments. Stiff muscles usually resolve with exercise, or light movement, especially after resting. For individuals whose symptoms are more limiting, doctors have had some success with medications such as quinine, or anticonvulsant drugs such as phenytoin. Physical therapy and other rehabilitative therapies are also sometimes used to improve muscle function.
Most individuals with myotonia congenita lead long, productive lives. Although muscle stiffness may interfere with walking, grasping, chewing, and swallowing, it is usually relieved with exercise.
The National Institute of Neurological Disorders and Stroke (NINDS) conducts research related to myotonia congenita and also supports additional research through grants to major research institutions across the country. Current research is exploring how, at the molecular level, the defective gene in myotonia congenita causes the specific symptoms of the disorder. Additional research is focused on developing animal models of the disorder to test potential treatments and therapies. Information from the National Library of Medicine’s MedlinePlus Myotonia Congenita