Polymyositis is a rare inflammatory disease that leads to muscle weakness, swelling tenderness, and tissue damage. It is part of a larger group of diseases called myositis.
Polymyositis affects the skeletal muscles. It is also known as idiopathic inflammatory myopathy. The exact cause is unknown, but it may be related to an autoimmune reaction or infection.
Polymyositis can affect people at any age. It most common in adults between ages 50 and 70, and in children ages 5 to 15. It affects women twice as often as men. It is more common in African Americans than Caucasians.
Polymyositis is a systemic disease, which means it affects the whole body. Muscle weakness and tenderness can be signs of polymyositis. A rash is a sign of a similar condition, dermatomyositis.
Common symptoms include:
You may also have:
Tests may include:
People with this condition also must be watched carefully for signs of cancer.
The main treatment is with corticosteroid medicines. The dose of medicine is slowly tapered off as muscle strength improves. This takes about 4-6 weeks. You will stay on a low dose of a corticosteroid medicine after that. Medicines to suppress the immune system, such as methotrexate and azathioprine, may be used for people who do not respond to corticosteroids.
Intravenous gamma globulin has been tried, with mixed results. Biologic drugs also may play in part in treating this condition but it is too soon to know.
If the condition is associated with a tumor, it may improve if the tumor is removed.
Response to treatment varies based on the complications. The 5-year mortality rate can be as high as 1 in 5 patients.
Many people, especially children, a period when no symptoms are present and recover. For most other people, immunosuppressant drugs can control the disease.
In adults, death may result from:
The major causes of death are cancer and lung disease.
Call your health care provider if you have symptoms of this disorder. Seek emergency treatment if you have shortness of breath and difficulty swallowing.
Nagaraju K, Lundberg IE. Inflammatory Diseases of Muscle and Other Myopathies. In: Firestein GS, Budd RC, Gabriel SE, et al, eds. Kelley's Textbook of Rheumatology. 9th ed. Philadelphia, Pa: Saunders Elsevier;2012:chap 85.
Miller FW, Polymyositis and Dermatomyositis. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 277.