Dermatomyositis and polymyositis are rare diseases that cause inflammation and weakness of muscles and some skin tissues. They are also known as “idiopathic inflammatory myopathies.” They affect both adults (usually ages 45 to 60) and children (usually ages 10 to 15), more females than males.
The cause is unknown, but they are thought to be autoimmune disorders. In autoimmune disorders, the immune system attacks the body’s own tissues. Small blood vessels in muscles and some skin tissues get damaged, which weakens muscle fibers and makes them break down. The disorders aren’t contagious or passed from parents to children.
Symptoms of dermatomyositis are a rash (on the face, chest, back, elbows, knees, and knuckles) and weakness of neck, shoulder, upper arm, hip, and thigh muscles. People may have trouble getting out of chairs, climbing stairs, lifting things, or reaching over their heads. Sometimes, trouble swallowing, sore muscles, tiredness, fever, hard bumps under the skin, and weight loss occur. The disease may also affect the lungs, heart, or gut. No rash occurs in polymyositis, but other symptoms are the same.
The health care provider makes a diagnosis based on your history, physical examination, blood tests, electromyography, and muscle biopsy. Blood tests can show muscle breakdown, inflammation, or antibodies. Electromyography measures how muscles are working. In a biopsy, the doctor removes a small piece of muscle that is sent for study.
Treatments may help the rash and muscle strength improve, but some muscles may be permanently weak. However, treatment may last for months or even years. Sometimes, the disease goes away on its own.
Corticosteroid drugs, especially prednisone, are the main treatment for inflammation. If corticosteroids don’t work, immunosuppressant drugs and immunoglobulins may be tried. Skin cream (such as prednisone and tacrolimus) may be used for the rash.
Muscle exercises are an important part of treatment. They’re for flexibility and help strengthen muscles. A physical therapist can create the right exercise program.
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Copyright © 2016 by Saunders, an imprint of Elsevier, Inc.
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