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Dermatomyositis

Dermatomyositis is a muscle disease that involves inflammation and a skin rash. It is a type of inflammatory myopathy.

Causes

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 this condition. It most often occurs in children age 5 to 15 and adults age 40 to 60. It affects women more often than men.

Polymyositis is a similar condition, but the symptoms do not include a skin rash.

Symptoms

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.

Exams and Tests

The health care provider will do a physical exam. Tests may include:

Treatment

The disease is treated with anti-inflammatory medicines called corticosteroids. Medicines to suppress the immune system may be used to replace the corticosteroids. These may include azathioprine, methotrexate or mycophenolate.

If the condition does not respond to these medicines, other drugs, such as biologics may be tried. Rituximab appears to be the most promising.

When your muscles get stronger, your provider may tell you to slowly cut back on your doses. Many 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.

Outlook (Prognosis)

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
  • Lung failure

The major causes of death with this condition are cancer and lung disease.

Possible Complications

Complications may include:

When to Contact a Medical Professional

Call your provider if you have muscle weakness or other symptoms of this condition.

References

Nagaraju K, Gladue HS, Lundberg IE. Inflammatory diseases of muscle and other myopathies. In: Firestein GS, Budd RC, Gabriel SE, McInnes IB, O'Dell JR, eds. Kelley and Firestein's Textbook of Rheumatology. 10th ed. Philadelphia, PA: Elsevier; 2017:chap 85.

National Organization for Rare Disorders. Dermatomyositis. Rarediseases.org Web site. rarediseases.org/rare-diseases/dermatomyositis/. Accessed March 7, 2017.

Review Date 2/8/2017

Updated by: Gordon A. Starkebaum, MD, Professor of Medicine, Division of Rheumatology, University of Washington School of Medicine, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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