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What is polymyositis?

Polymyositis is an inflammatory muscle disease that causes muscle weakness. Myositis means inflammation of muscle. Usually, polymyositis affects the muscles that are closest to the trunk of the body. Eventually, people with polymyositis have trouble when rising from a sitting position, climbing stairs, lifting objects, or reaching overhead. In some cases, muscles that are not close to the trunk of the body become affected as the disease progresses.

Polymyositis develops gradually over time, and it rarely affects persons younger than age 18. It is more common in women (by about two to one).

If the condition is accompanied by an inflammatory process that strikes the skin as well, it is called dermatomyositis.

Polymyositis can be present in combination with other illnesses. Both polymyositis and dermatomyositis can sometimes be associated with cancers, including lymphoma, breast, lung, ovarian, and colon cancer.

What causes polymyositis?

The cause of polymyositis is not known, but there are indications that heredity plays a role in the disease.

Current research suggests that the condition may occur when immune system cells infiltrate and attack muscle tissue (an autoimmune process).

Research into the workings of the immune system and what causes it to malfunction may result in more knowledge about the causes of polymyositis.

What are the symptoms of polymyositis?

The following are some symptoms of polymyositis. These symptoms may come and go:

  • Muscle weakness: This is the most common symptom. The muscles involved usually are those closest to the trunk of the body, and the onset of weakness is usually gradual, occurring over three to six months or rarely the symptoms come on rapidly.
  • Difficulty getting up from chairs, climbing stairs, or lifting objects: Some people also have trouble with getting up after lying down.
  • Difficulty swallowing
  • Muscle ache: In some cases, muscles ache and are tender to the touch.
  • Fatigue
  • Shortness of breath due to heart and lung involvement
  • Patchy red or violet rash around the eyes: Some people also get patchy, red skin over the knuckles, elbows and knees or a red rash on the neck and upper chest.
  • Fever
  • Weight loss

How is polymyositis diagnosed?

The diagnosis of the disease usually begins with a physician’s exam and blood testing. People who have polymyositis often have unusually high levels of muscle enzymes. The enzymes are released into the blood by muscle that is being damaged by inflammation. Routine blood and urine tests can check for internal organ abnormalities. Chest X-rays, mammograms, PAP smears, and other screening tests might be considered to look for signs of cancers that may arise with polymyositis. Additional testing can rule out other conditions resembling polymyositis.

Electromyography (EMG) and nerve conduction velocity studies are electrical tests of muscle and nerves that can show abnormal findings typical of polymyositis. These tests also can rule out other nerve-muscle diseases. Imaging of the muscles can show areas of muscle inflammation and can be used to find muscle biopsy sites.

Muscle biopsy is a surgical procedure in which muscle tissue is removed and examined. A muscle biopsy is used to confirm the presence of muscle inflammation typical only of polymyositis.

How is polymyositis treated?

Polymyositis is treated with high doses of corticosteroids as a first course of treatment. Corticosteroids are given because they can effectively decrease the inflammation in the muscles. Corticosteroids do not always adequately improve polymyositis. In these patients immunosuppressive medications are considered. These medicines include:

  • Methotrexate (brand names Rheumatrex® and Trexall®)
  • Azathioprine (brand name Imuran® and Azasan®)
  • Cyclophosphamide (brand name Cytoxan®)
  • Chlorambucil (brand name Leukeran®)
  • Cyclosporine (brand name Sandimmune®, Gengraf®, and Neoral®)
  • Tacrolimus (brand name Astagraf XL®, Hecoria®, Prograf®)
  • Mycophenolate (brand name CellCept®, Myfortic®)
  • Rituximab (brand name Rituxan®)

In severe cases of polymyositis, the intravenous infusion of immunoglobulins (IVIG) has been an effective treatment. Physical therapy also is important in the treatment of polymyositis.

With early medical treatment of the disease and disease flares, patients with polymyositis can do well. The disease frequently becomes inactive, enabling the patient to focus on muscle rehabilitation.

For more information, please see the following:

Muscular Dystrophy Association - USA
National Office
222 S. Riverside Plaza, Suite 1500
Chicago, IL 60606
Toll free: 800-572-1717

National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) Information Clearinghouse
National Institutes of Health
1 AMS Circle
Bethesda, MD 20892-3675
Tel: 301-495-4484
Toll free: 877-22-NIAMS (877-226-4267)

Myositis Association
1737 King Street
Suite 600
Alexandria, VA 22314
Tel: 703-299-4850 (DC Area)
Toll free: 800-821-7356
Fax: 703-535-6752

National Organization for Rare Disorders (NORD)
55 Kenosia Avenue
Danbury, CT 06810
Tel: 203-744-0100
Fax: 203-798-2291