Polymyositis/Dermatomyositis

What are polymyositis and dermatomyositis?

Polymyositis (PM) is a chronic disease that causes inflammation and weakness of the muscles. Dermatomyositis (DM) is a related disease in which a skin rash occurs along with the muscle problems of polymyositis. In about half of the people who have PM or DM, the heart muscle is affected. These diseases are rare.

How do they occur?

PM or DM probably occurs when the body's immune system attacks its own tissues. It is not known why this happens. An underlying cancer may also be related to the disease. PM or DM occurs twice as often in women as men. They occur most often between ages 50 and 70, or in children 5 to 15 years old.

What are the symptoms?

Polymyositis can begin suddenly or slowly. Symptoms may include:

weakness, especially in the hips, thighs, upper arms, and shoulders
muscle and joint pain
weight loss
fatigue
fever
tremors of the hands
shortness of breath, even at rest
problems swallowing.

If you have dermatomyositis, you also have a violet or deep reddish-purple rash.

How are they diagnosed?

Your health care provider will ask about your medical history and your symptoms. Your provider will examine you. The inflammation causes a breakdown of muscle cells, so you may have a blood test to look for abnormal amounts of broken cells. Other types of tests might include:

biopsy of the involved area (the removal of a small sample of muscle after an anesthetic) to check for inflammation
an electromyogram, or EMG, a test that looks at muscle strength and function.

How are they treated?

There is no known cure for PM/DM. If diagnosed with polymyositis, treatments might include:

ongoing physical therapy to prevent further weakness
supportive care for other symptoms such as shortness of breath or pain
prednisone or other anti-inflammatory drugs. These drugs work better for some people than for others. If further treatment is needed, powerful drugs that interfere with the body's normal immune system may be used. These are the same drugs used to control the rejection problem in heart and kidney transplants and must be used very carefully.

You may need to see a rheumatologist, a specialist in diseases of the connective tissue.

Call your health care provider right away if you have shortness of breath and trouble swallowing.

How long will effects last?

It is difficult to predict the course of this disease. Once diagnosed you might:

have a severe episode at the time of diagnosis, and then do well
have ongoing flare-ups of the disease, but little progression
have it affect your breathing muscles or heart. If you have these complications, you will need to work even more closely with your health care provider to manage your disease.

Disclaimer: This content is reviewed periodically and is subject to change as new health information becomes available. The information provided is intended to be informative and educational and is not a replacement for professional medical evaluation, advice, diagnosis or treatment by a healthcare professional.

HIA File BJM3226F.HTM Release 9.0/2006