May also be called: Idiopathic Inflammatory Myopathy

Polymyositis (pol-ee-my-uh-SY-tis) is an uncommon inflammatory disease that causes weakness, pain, and swelling in skeletal muscles (voluntary muscles that connect bones). It is one of three diseases that are classified as chronic inflammatory myopathies or myositis.

More to Know

Polymyositis can occur in people of all ages, but is most common in adults over the age of 30. Women are more likely to get the disease than men.

With polymyositis, something causes the immune system to attack healthy muscle tissue. Muscles most affected by polymyositis include the hips, thighs, shoulders, neck, and upper arms.

In addition to progressive muscle weakness, swelling and tenderness, people with polymyositis may have shortness of breath, fatigue, joint pain, fever, difficulty swallowing or speaking, loss of appetite, and weight loss. Symptoms appear very gradually, can vary greatly, and tend to get worse over time.

There is no cure for polymyositis, but it can be treated with immunosuppressant medications and intravenous gamma globulin (a donated blood product with healthy antibodies). A doctor might also recommend physical therapy and speech therapy to help improve muscle function.

Keep in Mind

Polymyositis is a serious disease than can result in life-threatening complications such as heart disease, lung disease, and pneumonia. With treatment, however, most people see improvement in their condition. Some might even experience remission (an absence of symptoms).

All A to Z dictionary entries are regularly reviewed by KidsHealth medical experts.