There is no effective treatment, but gene therapy is being studied. The illness progresses very slowly and, because the legs are only mildly affected, patients maintain the ability to walk. The disorder's striking feature is myotonia, the failure of muscles to relax normally after sudden, vigorous use. The genetic abnormality causing myotonic dystrophy is now known to reside on chromosome 19. In older patients, especially men, polymyositis is often linked to cancer for unknown reasons.
Patients have difficulty lifting, raising their arms overhead, and climbing stairs.
Medical evaluation must rule out the possibility of unrecognized malignancy. This disease causes fluctuating muscle weakness, especially in muscles controlling eye movements, eye opening, facial mobility, and swallowing. In severe cases, the condition affects all muscles of the body, including those involved with respiration. The severity of weakness can vary from day to day or even in the course of a single day. The disease is caused by a defect in neuromuscular transmission, in which the chemical signal between motor nerves and muscles is improperly transmitted.