Q. A friend of mine was recently diagnosed with something called polymyositis. She had been getting weaker over the past several months. Neither of us had ever heard of this condition before. What causes it? Is it contagious? How serious is it? Where can we get more information about this problem?

A. Polymyositis is a rare condition that weakens muscles. The cause is unknown, but there are several treatments that can help.

The word polymyositis in Greek literally means inflammation of multiple muscles. The ailment is one of several related disorders--dermatomyositis, juvenile myositis and inclusion body myositis are others--that can cause muscle weakness and pain. About 30,000 people in the United States have one of them.

Polymyositis may stem from a combination of factors, including genetics, viral infection and an autoimmune process. Autoimmune refers to the body's immune system going awry and attacking normal tissue, in this case the muscles. Polymyositis is not contagious.

Although the condition may start at any age, it typically affects young adults, women more often than men. It starts gradually, usually first weakening the hip and shoulder muscles. A person with polymyositis might have difficulty getting out of a chair or up from the floor. Climbing stairs gets more difficult, as does lifting things above one's head.

The weakness is usually painless. But some people have pain in their muscles or pain when using them. At times, the muscles can also be tender.

If polymyositis affects the muscles of the esophagus or chest, a person may have trouble swallowing or breathing normally. Occasionally the heart muscle is affected, which can lead to irregular heartbeats or even heart failure.

Because the early symptoms can be subtle or mimic common problems, polymyositis can be difficult to diagnose. Many people see several doctors over months or even years before the condition is recognized.

Once a doctor suspects the condition as a cause for a patient's muscle weakness, there are several tests to confirm it.

Other conditions that can cause muscle weakness that looks like polymyositis include hypothyroidism (underactive thyroid gland), muscular dystrophy, chronic alcoholism and infection with the human immunodeficiency virus (HIV) that causes AIDS.

Several medications can cause muscle weakness, so people experiencing the problem should be sure to check with a doctor or pharmacist to determine whether a drug might be to blame.

In about 10 percent of cases, polymyositis occurs in association with certain cancers. In fact, the muscle weakness can show up before the cancer is discovered. About a third of the time, the condition develops in the presence of other autoimmune disorders, such as scleroderma, rheumatoid arthritis and lupus.

When the condition develops along with certain kinds of skin rashes, it is called dermatomyositis. The rash tends to occur on the eyelids, face, knuckles, elbows and knees.

The treatments for polymyositis and dermatomyositis are similar. Steroids such as prednisone are used for months or even years. Long-term use of steroids can cause significant side effects, so patients should check with doctors for information on what to look out for and how to minimize risk.

If steroids aren't effective, a doctor might prescribe powerful drugs that block the actions of the immune system. Two medicines often used in severe cases are azathioprine and methotrexate. Another treatment is getting immune globulin (antibodies from blood bank blood) intravenously. In addition to medicines, physical therapy is often recommended.

Although complications of polymyositis can lead to premature death, most people with the condition are able to lead relatively normal lives.

For more information about any of these muscle disorders, contact the Myositis Association of America, 755 Cantrell Ave., Suite C, Harrisonburg, VA 22801. The association can be reached by telephone at 540-433-7686; its Web site address is www.myositis.org.

Jay Siwek, chairman of the department of family medicine at Georgetown University Medical Center, practices at the Fort Lincoln Family Medicine Center and Providence Hospital in Northeast Washington.

Consultation is a health education column and is not a substitute for medical advice from your physician. Send questions to Consultation, Health Section, The Washington Post, 1150 15th St. NW, Washington, DC 20071. Questions cannot be answered personally.