Polymyositis is one type of inflammatory myopathy. Inflammatory myopathies are muscle diseases that involve redness, soreness, and swelling (inflammation) of the muscles. Polymyositis causes decreased muscle power. It affects the connective tissues of the body (connective tissue disease). It is often associated with diseases in which the body attacks its own cells (autoimmune diseases). Polymyositis begins gradually. It generally affects adults in their 30s to 50s.


The cause is often unknown. Some cases are caused by a bacteria, virus, or parasite infection. This can trigger autoantibodies, which attack normal, healthy cells.


  • The most common symptom is muscle weakness. This often affects muscles close to the trunk of the body (proximal). Muscles not close to the trunk (distal) may also be affected later on in the disease.

  • Eventually, patients have trouble:

  • Rising from a sitting position.

  • Climbing stairs.

  • Lifting objects.

  • Reaching overhead.

  • Trouble swallowing (dysphagia) may occur.

  • Rarely, the muscles ache and are tender to touch.

Associated conditions include:

  • Fingers, toes, nose, and ears that turn pale when exposed to cold (Raynaud's phenomenon).

  • Other connective tissue diseases. This may include lupus, rheumatoid arthritis, or scleroderma.

  • Heart disease. This is caused by inflammation of the heart muscle.


Diagnosis can be difficult. It is based on symptoms and a thorough exam. Further testing may be done, including:

  • Blood tests to check for high levels of muscle enzymes, which suggest muscle damage, and specific autoantibodies.

  • Computerized magnetic scan (MRI).

  • Test to check electrical activity of the muscle (electromyography).

  • Exam of a muscle tissue sample (biopsy).


There is no cure. Treatment can improve muscle strength and function. The earlier treatment is started, the more effective it is. Early treatment often means fewer complications.

  • Drug treatments may include:

  • Corticosteroids, especially prednisone. Patients often improve in about 2 to 4 weeks. However, drug therapy may be needed for years. Long-term use of corticosteroids can have serious side effects. Your caregiver may advise supplements or may prescribe other medicines.

  • Corticosteroid-sparing agents.

  • Intravenous immunoglobulin (IVIG). This contains healthy antibodies from blood donors.

  • Immunosuppressive therapies, such as tacrolimus.

  • Physical therapy is often advised. This helps stop muscles from wasting away (atrophy).

  • Chewing and swallowing can be more difficult later on in the disease. A registered dietitian can teach you how to make foods that are easy to eat.

  • Speech therapy can be helpful if your swallowing muscles are weakened.

Results from therapy vary depending on the severity of the disease. Rarely, the disease may be life-threatening to patients with severe, progressive muscle weakness, dysphagia, malnutrition, pneumonia, or respiratory failure.


  • Stay active. An exercise routine can help you build and maintain muscle strength. It is important to get a detailed plan and recommendations from your caregiver or physical therapist before starting an exercise program.

  • Rest when you are tired. Do not wait until you are exhausted to rest. Learn to pace yourself.


You develop new or worsening muscle weakness.


  • You have trouble swallowing or speaking.

  • You develop shortness of breath.


The Myositis Association: www.myositis.org

National Institute of Neurological Disorders and Stroke: www.ninds.nih.gov