Polymyositis is a systemic connective tissue disease 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 and 70 years old, or in children between 5 and 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 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 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. Each year, between 2 and 10 people per million develop the disease.
- muscle weakness, proximal muscles (shoulders, hips, etc.)
- muscle pain
- difficulty swallowing
- Shortness of breath
- hand tremor
Signs and tests
- MRI of affected muscles
- muscle biopsy
- serum creatinine, elevated
- serum aldolase, elevated
- CPK, elevated
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 may be continued indefinitely. In people who fail to respond to corticosteroids, medications to suppress the immune system may be used.
If the condition is associated with a tumor, the condition may improve if the tumor is removed.
Remission (a period when no symptoms are present) and recovery occur in many patients, especially children. For most others, immunosuppressant drugs can control the disease. In adults, death may result from severe and prolonged muscle weakness, malnutrition, Pneumonia, or respiratory failure. The probable outcome is usually worse if there is chest involvement.
- associated malignancy
- heart disease, lung disease, or abdominal complications
- calcium deposits in the affected muscles, especially in children with the disease
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.
by Brenda A. Kuper, M.D.