Polymyositis: How common is it?

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.

It is called dermatomyositis when the skin is also affected. It can cause skin rashes all over the body.

Both polymyositis and dermatomyositis are chronic diseases. This means that they can last a very long time.

With both forms of the disease, there may be times when the symptoms are stronger (active periods) and then periods when the symptoms lessen (remissions).



Dermatomyositis and polymyositis are twice as common in women as in men. They  can occur at any age but are most common in children and adults over age 50. More adults than children get these diseases. One to five new cases per 100,000 are seen each year.

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.

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