The inflammatory myopathies are a group of diseases, with no known cause, that involve chronic muscle inflammation accompanied by muscle weakness.
The majority of these disorders are considered to be autoimmune disorders, in which the body’s immune response system that normally defends against infection and disease attacks its own muscle fibers, blood vessels, connective tissue, organs, or joints.
These rare disorders may affect both adults and children and may include:
- Polymyositis, which affects skeletal muscles (involved with making movement).
- Dermatomyositis, which includes a skin rash and progressive muscle weakness.
General symptoms of chronic inflammatory myopathy include progressive muscle weakness that starts in the proximal muscles--those muscles closest to the trunk of the body. Other symptoms include fatigue after walking or standing, tripping or falling, and difficulty swallowing or breathing. Polymyositis and dermatomyositis are more common in women than in men. Dermatomyositis is more common in children.
Most cases of dermatomyositis respond to therapy. Approximately one-third of individuals with juvenile-onset dermatomyositis recover from their illness, one-third have a relapsing-remitting course of disease, and the other third have a more chronic course of illness. The prognosis for polymyositis varies. Most individuals respond fairly well to therapy, but some people have a more severe disease that does not respond adequately to therapies and may have significant disability.
The chronic inflammatory myopathies can’t be cured, but many of the symptoms can be treated. Options include medication, physical therapy, and rest. Polymyositis and dermatomyositis are first treated with high doses of corticosteroid drugs such as prednisone. Immunosuppressant drug may reduce inflammation in individuals who do not respond well to prednisone. Some individuals may use a topical cream to treat skin problems associated with the disorder.
Keeping active is important. Rehabilitation medicine can help manage symptoms by prescribing therapies, medications, braces, or equipment to maximize function. Physical therapy is usually recommended to prevent muscle atrophy as well as to maintain muscle strength and range of motion. Occupation therapy may be needed to help with arm splints, energy conservation strategies, and recommend adaptive equipment.
NIH: National Institute of Neurological Disorders and Stroke