Overview

Muscles affected by polymyositis (frontal view) Muscles affected by polymyositis (back view)
Polymyositis mostly affects the muscles of the hips and thighs, the upper arms, the top part of the back, the shoulder area and the neck.

What is polymyositis (PM)?

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 response to cell damage.

Another word for inflammatory myopathy is myositis. The myo root means muscle, and the itis root means inflammation; so a myositis is an inflammatory muscle disease.

What are the symptoms of PM?

The muscles of the shoulders, upper arms, hips, thighs and neck display the most weakness in PM. There also can be pain or tenderness in the affected areas, as well as swallowing problems and inflammation of the heart and lung muscle tissues. For more, see Signs and Symptoms.

What causes PM?

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.

PM is not a genetic disorder, although there may be genetic factors that make it more or less likely that an inflammatory myopathy will develop. For more, see Causes/Inheritance.

What is the progression of PM?

PM usually begins after age 20, and its progression is gradual. Although inflammatory myopathies like PM can lead to great discomfort for at least a period of time, effective treatments are available, and for the most part these conditions aren’t life-threatening. In fact, many people recover partially or completely from PM.

What is the status of research on PM?

New research is rapidly leading to increased understanding of PM and to more successful treatments. Scientists are examining factors that may trigger PM such as viruses, certain drugs or vaccines. All these factors are being studied so inflammatory myopathies like PM can someday be better understood, treated or perhaps prevented entirely. For more, see Research.

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