Paramyotonia congenita is an inherited condition that causes stiffness and enlargement of muscles, particularly leg muscles.
Paramyotonia congenita is passed on in families as an autosomal dominant trait. This means that males and females are affected equally; it also means that if one parent has the trait, the offspring have a 75% chance of also having the condition.
Paramyotonia congenita is present from birth on. In some cases, the symptoms appear to grow more mild as the patient ages.
Causes and symptoms
Paramyotonia congenita is believed to be caused by a defect in the chloride channels of the muscles. As a result, the relaxation phase of the muscles is impaired, resulting in prolonged muscle contraction and stiffness. This "overuse" of the muscle results in the muscle becoming enlarged and bulky (called muscle hypertrophy).
Symptoms of paramyotonia congenita include stiffness and enlargement of various muscle groups, particularly those in the legs. The muscle stiffness of paramyotonia congenita is often exacerbated by cold temperatures and inactivity and relieved by warmth and exercise .
Electromyographic (EMG) testing involves placing a needle electrode into a muscle and measuring its electrical activity. EMG testing in paramyotonia congenita may reveal differences between electrical activity in a warm muscle and electrical activity in a cooled muscle. There are a number of genetic defects that are associated with the chloride channel defect of paramyotonia congenita, some of which can be revealed through genetic testing.
Paramyotonia congenita is diagnosed and treated by neurologists.
Paramyotonia congenita is usually mild enough not to require any treatment at all. If muscle stiffness is truly problematic, quinine or anticonvulsant medications (such as phenytoin) may improve functioning.
Paramyotonia congenita has an excellent prognosis. Although annoying, it does not cause significant disability, and the patient usually learns to make lifestyle adjustments that prevent exacerbations (for example, dressing warmly and avoiding exposure to cold).
Brown, Robert H., and Jerry R. Mendell. "Muscular Dystrophies and Other Muscle Diseases." In Harrison's Principles of Internal Medicine, edited by Eugene Braunwald, et al. NY: McGraw-Hill Professional, 2001.
Rose, Michael, and Robert C. Griggs. "Hereditary Nondegenerative Neuromuscular Disease." In Textbook of Clinical Neurology, edited by Christopher G. Goetz. Philadelphia: W. B. Saunders Company, 2003.
National Institute of Neurological Disorders and Stroke (NINDS). NINDS Myotonia Congenita Information Page. November 8, 2001. <http://www.ninds.nih.gov/health_and_medical/disorders/myotoniacongenita.htm> (June 3, 2004).
Rosalyn Carson-DeWitt, MD