Polymyositis is a relatively uncommon inflammatory disease that leads to muscle weakness, swelling (inflammation), tenderness, and damage. It is part of a larger group of diseases called myositis.
Causes, incidence, and risk factors
Polymyositis is a skeletal muscle disease that is also known as idiopathic inflammatory myopathy. The cause is unknown. An autoimmune reaction or infection of the skeletal muscle may cause the disease.
Polymyositis can affect people at any age, but it most commonly occurs between ages 50 and 70, or in children ages 5 to 15. It affects women twice as often as men. It is more common in African Americans than Caucasians. Overall, about 1 in 100,000 people are diagnosed with some form of inflammatory myopathy each year.
Other types of inflammatory muscle diseases exist, including inclusion body myositis.
Polymyositis is a systemic disease, which means it affects the whole body. Symptoms include:
Patients with this condition must be carefully monitored for cancer.
The main treatment is with corticosteroid medications. When muscle strength improves, usually in 4 to 6 weeks, the medication is slowly tapered off. Maintenance therapy with prednisone may be continued indefinitely. In people who fail to respond to corticosteroids, medications to suppress the immune system, such as methotrexate and azathioprine, may be used.
Intravenous gamma globulin has been tried, with mixed results. It is too soon to know what role biologic drugs may play in treating this condition.
If the condition is associated with a tumor, it may improve if the tumor is removed.
Response to treatment varies, and it depends on whether there are complications. The 5-year mortality can be as high as 20%.
Many patients, especially children, go into remission (a period when no symptoms are present) and recover. For most other people, immunosuppressant drugs can control the disease.
Michael E. Makover, MD, professor attending in Rheumatology at the New York University Medical Center, New York, NY. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.