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Polymyositis

by Robert S. Dinsmoor

A rare inflammatory condition that weakens various muscles throughout the body. The word polymyositis is actually Greek for “inflammation of multiple muscles.” It is estimated that 30,000 people in the United States have polymyositis (PM) or related disorders (such as dermatomyositis and inclusion body myositis) that cause muscle weakness and pain. In some people, PM lasts a matter of months and then disappears. In others, it can get worse with time and be difficult to treat.

The underlying cause of PM is not thoroughly understood. What is known is that white blood cells infiltrate the muscle cells and release certain enzymes that damage muscle fibers. When PM affects the upper extremities, people may have trouble with such routine tasks as lifting things, brushing their hair, shaving, and hanging up clothing. When it affects the lower extremities, people may have difficulty walking up stairs or rising from low seats or a squatting position. PM can also affect muscles of the esophagus, causing difficulty in swallowing; muscles of the chest, making breathing difficult; and the heart muscle, leading to irregular heartbeats or even heart failure.

A number of other disorders, such as underactive thyroid gland, muscular dystrophy, chronic alcoholism, and HIV infection, can cause symptoms similar to those of PM, so it can be difficult to diagnose. Once diagnosed, it can be treated with drugs to reduce inflammation and the damage it causes. Usually, the first line of therapy is corticosteroids. Corticosteroids have some serious side effects, however. If they are used at high doses for a long time, they can cause weakness and wasting of the muscles, and muscle weakness is already the main problem in PM. Once the inflammation of PM is under control, therefore, the corticosteroid dose is tapered, that is, gradually decreased. If the tapering causes PM symptoms to return, which sometimes happens, or if the corticosteroids don’t adequately relieve inflammation in the first place, powerful immunosuppressive drugs such as azathioprine and methotrexate can be added. Recently, doctors have begun using injections of immune gamma globulin (an immunizing agent from human blood) to treat people with PM. This is sometimes extremely effective. In addition, a program of physical therapy is used to prevent muscle shortening, maintain the individual’s range of motion, and restore the ability to carry out normal daily activities.

For more information about polymyositis, call the Myositis Association of America at (800) 821-7356 or visit its Web site at www.myositis.org.

Last Reviewed on June 27, 2012

Robert S. Dinsmoor is a medical writer and editor based in Massachusetts.

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