A systemic connective tissue disease, which is characterized by inflammation and degeneration of the muscles.

Causes, incidence, and risk factors

The cause of this disorder is unknown. It is thought that an autoimmune reaction or a viral infection of the skeletal muscle may cause the disease. It can affect people at any age, but most commonly occurs in those between 50 to 70 years old, or in children between 5 to 15 years old. It affects women twice as often as men. Muscle weakness may appear suddenly or occur slowly over weeks or months. There may be difficulty with raising the arms over the head, rising from a sitting position, or climbing stairs. The voice may be affected through weakness of the throat muscles. Joint pain , inflammation of the heart , and pulmonary (lung) disease may occur. A similar condition, called dermatomyositis , is evident when a dusky, red rash appears over the face, neck, shoulders, upper chest, and back. A malignancy may be associated with this disorder. The annual incidence of polymyositis ranges from 2 to 10 new cases per million persons.

Signs and tests

Treatment

The disease is treated with corticosteroid medications. When an improvement in muscle strength is achieved, usually in 4 to 6 weeks, the medication is slowly tapered off. Maintenance therapy with prednisone is usually continued indefinitely. In people who fail to respond to corticosteroids, medications to suppress the immune system may be indicated. If the condition is associated with a tumor , the condition may improve if the tumor is removed.

Expectations (prognosis)

Remission (a period when no symptoms are present) and recovery have been reported, especially in children. In adults, death may result from severe and prolonged muscle weakness , malnutrition , pneumonia , or respiratory failure. The probable outcome is usually worse if chest involvement is present.

Complications

Calling your health care provider

Call your health care provider if symptoms of this disorder occur; shortness of breath and difficulty swallowing can indicate an urgent need for treatment.