Polymyositis and Dermatomyositis

  • Medical Author:
    William C. Shiel Jr., MD, FACP, FACR

    Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

  • Medical Editor: Catherine Burt Driver, MD
    Catherine Burt Driver, MD

    Catherine Burt Driver, MD

    Catherine Burt Driver, MD, is board certified in internal medicine and rheumatology by the American Board of Internal Medicine. Dr. Driver is a member of the American College of Rheumatology. She currently is in active practice in the field of rheumatology in Mission Viejo, Calif., where she is a partner in Mission Internal Medical Group.

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Myositis (Muscle Inflammation)...Check the Meds!

Statin drugs are known to cause muscle pains and inflammation around the muscle cells (myositis). It should also be noted that the risk of muscle injury is greater when a statin is combined with other drugs that also cause muscle damage by themselves.

Polymyositis facts

  • Polymyositis and dermatomyositis (PM/DM) are chronic inflammatory diseases of muscle.
  • Muscle weakness is the most common symptom of PM/DM.
  • The cause of PM/DM is unknown.
  • Diagnosis of PM/DM involves physical examination of muscle strength, blood tests for muscle enzymes, electrical tests of muscle and nerves, and is confirmed by muscle biopsy.
  • Treatment of PM/DM involves high doses of cortisone-related medications, immune suppression, and physical therapy.

What is polymyositis?

Polymyositis is a disease of muscle featuring inflammation of the muscle fibers. The cause of the disease is not known. It begins when white blood cells, the immune cells of inflammation, spontaneously invade muscles. The muscles affected are typically those closest to the trunk or torso. This results in weakness that can be severe. Polymyositis is a chronic illness featuring progressive muscle weakness with periods of increased symptoms, called flares or relapses, and minimal or no symptoms, known as remissions.

Polymyositis is slightly more common in females. It affects all age groups, although its onset is most common in middle childhood and in the 20s. Polymyositis occurs throughout the world. Polymyositis can be associated with skin rash and is then referred to as "dermatomyositis." Dermatomyositis in children is referred to as juvenile dermatomyositis. "Amyopathic dermatomyositis" is the term used to describe people who have skin changes compatible with dermatomyositis but do not have diseased muscle involvement.

Polymyositis can also affect other areas of the body and is, therefore, referred to as a systemic illness. Occasionally, it is associated with cancer or with other diseases of connective tissue (such as systemic lupus erythematosus, scleroderma, and rheumatoid arthritis).

Medically Reviewed by a Doctor on 2/19/2015
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