Polymyositis is an inflammatory muscle disease that causes varying degrees of decreased muscle power. The disease has a gradual onset and generally begins in the second decade of life. Polymyositis rarely affects persons under the age of 18. The most common symptom is muscle weakness, usually affecting those muscles that are closest to the trunk of the body (proximal). Eventually, patients have difficulty rising from a sitting position, climbing stairs, lifting objects, or reaching overhead. In some cases, distal muscles (those not close to the trunk of the body) may also be affected later in the course of the disease. Trouble with swallowing (dysphagia) may occur. Very rarely, the muscles ache and are tender to touch. The disease may be associated with other collagen vascular, autoimmune or infectious disorders
Treatment for polymyositis generally consists of a steroid drug called prednisone. For patients in whom prednisone is not effective, immunosuppressants such as azathioprine and methotrexate may be prescribed. Intravenous immunoglobulin has also helped difficult cases. Physical therapy is usually recommended to avoid muscle atrophy.
The prognosis for polymyositis varies. Response to therapy varies from very good to satisfactory. Some patients have a more severe disease that does not respond adequately to therapies and are left with significant disability. Death is rare but may occur in patients with severe and progressive muscle weakness, dysphagia, malnutrition, pneumonia, or respiratory failure.