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 2 to 1).

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 3 to 6 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.

Last reviewed by a Cleveland Clinic medical professional on 04/02/2019.


  • Muscular Dystrophy Association. Polymyositis (PM). Accessed 4/3/2019.
  • Myositis Association. Polymyositis. Accessed 4/3/2019.
  • Hellmann DB, Imboden JB, Jr. Rheumatologic & Immunologic Disorders. In: Papadakis MA, McPhee SJ, Rabow MW. eds. Current Medical Diagnosis & Treatment 2015. New York, NY: McGraw-Hill; 2014.
  • Ropper AH, Samuels MA, Klein JP. Chapter 48. Diseases of Muscle. In: Ropper AH, Samuels MA, Klein JP. eds. Adams & Victor's Principles of Neurology, 10e. New York, NY: McGraw-Hill; 2014.

Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy