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:
- Muscle weakness, stiffness, or soreness
- Problems swallowing
- Purple color to the upper eyelids
- Purple-red skin rash
- Shortness of breath
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.
Tests may include:
- Blood tests to check muscle enzyme levels
- Blood tests for autoimmune diseases
- Magnetic resonance imaging
- Muscle biopsy
- Skin biopsy
- Other screening tests for cancer
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.