Polymyositis is one of the inflammatory myopathies, a group of muscle diseases that involves inflammation of the muscles or associated tissues, such as the blood vessels that supply the muscles. A myopathy is a muscle disease, and inflammation is the response to cell damage.
In most cases, the cause of an inflammatory myopathy is unclear. For some reason, the body’s immune system turns against its own muscles and damages muscle tissue in an autoimmune process. In PM, the inflammatory cells of the immune system directly attack muscle fibers.
Polymyositis signs and symptoms include: Progressive muscle weakness; difficulty swallowing; difficulty speaking; mild joint or muscle tenderness; fatigue or shortness of breath.
Polymyositis typically affects the muscles closest to the trunk, particularly those in the hips, thighs, shoulders, upper arms and neck. The weakness is symmetrical, meaning it involves muscles on both the left and right sides of ones body. The disease worsens over time. As muscle weakness progresses, a patient finds it difficult to climb stairs, rise from a seated position, lift objects or reach overhead.
Polymyositis is a highly treatable disease. Some people recover completely, while others experience greatly diminished symptoms for long periods of time. Several years of treatment to suppress the immune system may be necessary to achieve these results. Drugs that suppress the immune system are the mainstay of therapy for PM. The first drug used in the treatment of PM is usually a corticosteroid, such as prednisone. Those who don’t recover completely may need to continue on at least a low dose of medication to control the autoimmune attack of PM throughout their lives.
Polymyositis can occur at any age, but it mostly affects adults in their 30s, 40s or 50s. It's more common in blacks than in whites, and women are affected more often than men are. Polymyositis signs and symptoms usually develop gradually, over weeks or months.