Dermatomyositis is a muscle disease that involves inflammation and a skin rash. It is a type of inflammatory myopathy.
The cause of dermatomyositis is unknown. Experts think it may be due to a viral infection of the muscles or a problem with the body's immune system. It may also occur in people who have cancer in the abdomen, lung, or other parts of the body.
Anyone can develop dermatomyositis. It most often occurs in children age 5 to 15 and adults age 40 to 60. Women develop this condition more often than men.
Polymyositis is a similar condition, but the symptoms do not include a skin rash.
Symptoms may include:
The muscle weakness may come on suddenly or develop slowly over weeks or months. You may have trouble raising your arms over your head, getting up from a sitting position, and climbing stairs.
The rash may appear on your face, knuckles, neck, shoulders, upper chest, and back.
The disease is treated with anti-inflammatory medicines called corticosteroids. You may also take drugs to suppress the immune system such as methotrexate, azathioprine, and hydroxychloroquine to treat the skin rash.
If the condition does not respond to these medicines, other drugs that suppress the immune system may be tried.
When your muscles get stronger, your doctor may tell you to slowly cut back on your doses. Most people with this condition must take a medicine called prednisone for the rest of their lives.
If a cancer is causing the condition, the muscle weakness and rash may get better when the tumor is removed.
Symptoms may go away completely in some people, such as children.
The condition may be fatal in adults due to severe muscle weakness, malnutrition, pneumonia, or lung failure. The major causes of death with this condition are cancer and lung disease.
Call your health care provider if you have muscle weakness or other symptoms of this condition.
Jorizzo JL, Vleugels RA. In: Bolognia JL, Jorizzo JL, Schaffer JV, et al, eds. Dermatology. 3rd ed. Philadelphia, PA: Elsevier Mosby; 2012:chap 42.
Last reviewed on: 1/20/2015
Reviewed by: Gordon A. Starkebaum, MD, professor of medicine, division of rheumatology, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.