Polymyositis is a chronic, progressive disease of connective tissue characterized by edema, inflammation, and degeneration of skeletal muscles. When the disease occurs with skin involvement, it is called dermatomyositis. Polymyositis and dermatomyositis develop slowly and have frequent exacerbations and remissions. Adults between ages 30 and 50 are most often affected. Women develop this condition twice as often as men, and it is much more common in African Americans.
Polymyositis is an idiopathic disease. Viral, parasitic, and bacterial infections are rarely found, so an autoimmune etiology is suspected. Nearly one-third of cases are associated with other connective-tissue disorders, such as RA and systemic lupus erythematosus. Other cases, particularly among elderly persons, are associated with malignancies, especially of the lung and breast.
Signs and Symptoms
Polymyositis usually develops insidiously over a period of a few months to a few years. The most frequent initial manifestation of the disease is muscle weakness in the hips and thighs. Consequently, the affected individual often reports difficulty in ascending or descending stairs or difficulty in rising from a sitting or kneeling position. Occasionally, the disease localizes in specific muscle groups, weakening only the neck, shoulder, or quadriceps muscles. Later symptoms include dysphagia and respiratory difficulties. In rare instances, the disease may appear as an acute condition, with the rapid onset and development of the symptoms noted.
When the disease develops as dermatomyositis, the previously mentioned symptoms may be preceded or accompanied by the appearance of a telltale lilac-colored rash on the eyelids, bridge of the nose, the cheeks, forehead, chest, elbows, and knees. The rash-covered portions of the body may itch severely. Dermatomyositis also may be accompanied by edema around the eye sockets.
A muscle biopsy may reveal tissue changes characteristic of polymyositis, such as muscle fiber necrosis, infiltration of the muscle tissue with inflammatory cells (leukocytes), and patterns of tissue degeneration and regeneration. Blood testing typically indicates increased serum levels of creatine kinase (CK), an enzyme normally present in skeletal muscles. The ESR also is usually elevated.
High doses of corticosteroid drugs are often administered to bring the disease under control, followed by lower maintenance doses over a period of years. Cytotoxic drugs also may be used to lower the number of inflammatory cells affecting the muscles, especially if the response to corticosteroids is poor. Injections of immunoglobulins may inhibit the attack of muscle tissue by antibodies. Bed rest during an acute attack is beneficial. Physiotherapy and physical rehabilitation to regain muscle function are important components of the treatment process.
Drug therapy using the biologic injectable rituximab has been tested using small groups of clients. It has been found to improve muscle strength and skin rash. The U.S. Food and Drug Administration has not approved this drug for treatment of polymyositis, so it would need to be prescribed as an off-label usage. No other significant complementary therapy is indicated.
Encourage clients to pace activities to counteract muscle weakness. Explain the disease and its complications to clients and family members. Advise a low-sodium diet to prevent fluid retention. Discuss the side effects of corticosteroid therapy (weight gain, hypertension, edema, acne, and easy bruising), and remind clients that side effects are diminished after drugs are discontinued.
The prognosis is variable. Roughly half of those affected by polymyositis recover within 5 years and can discontinue therapy. Some individuals must remain on drug therapy indefinitely; others die from acute cardiac, pulmonary, or renal complications. Generally, the prognosis worsens with age.
There is no specific prevention for polymyositis.