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Polymyositis is a rare inflammatory disease. It 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. This 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 to 6 weeks. You will stay on a low dose of a corticosteroid medicine after that. Medicines to suppress the immune system 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. Rituximab appears to be the most promising.
If the condition is associated with a tumor, it may improve if the tumor is removed.
Response to treatment varies based on the complications. As many as 1 in 5 people may die within 5 years of having the condition.
Many people, especially children, recover from the illness and do not need ongoing treatment. For most adults, however, immunosuppressant drugs are needed to control the disease.
In adults, death may result from:
The major causes of death are cancer and lung disease.
Complications may include:
Call your health care provider if you have symptoms of this disorder. Seek emergency treatment if you have shortness of breath and difficulty swallowing.
Greenberg SA. Inflammatory myopathies. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 69.
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: Elsevier Saunders; 2012:chap 85.
Oddis CV, Reed AM, Aggarwal R, et al. Rituximab in the treatment of refractory adult and juvenile dermatomyositis and adult polymyositis: a randomized, placebo-phase trial. Arthritis Rheum. 2013; 65:314. PMID: 23124935 www.ncbi.nlm.nih.gov/pubmed/23124935.
Reviewed By: Gordon A. Starkebaum, MD, Professor of Medicine, Division of Rheumatology, University of Washington School of Medicine, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.