Polymyositis is a relatively uncommon inflammatory disease that causes significant muscle weakness.
Causes, incidence, and risk factors
Polymyositis is a skeletal muscle disease also known as idiopathic inflammatory myopathy. The cause of this disorder is unknown. It is thought that an autoimmune reaction or a viral infection of the skeletal muscle may cause the disease.
It can affect people at any age, but most commonly occurs in those between 50 and 70 years old, or in children between 5 and 15 years old. 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.
A similar condition, called


