Polymyositis (PM)

Clinical Trials

About clinical trials




MDA-supported scientists are studying the underlying mechanisms that cause inflammatory myopathies, the group of diseases to which polymyositis (PM) belongs. Understanding precisely why and how the immune system attacks muscle tissue in PM will likely lead to better treatments for the disease.

One research team is studying inflammatory myopathies in dogs. These diseases appear to be similar in dogs and humans, and it is believed that this project may generate deeper understanding of human PM, and lead to new tools for diagnosis and treatment.

Medical Management

Polymyositis (PM) is a highly treatable disease. Some people recover completely, while others experience greatly diminished symptoms for long periods of time. Several years of treatment to suppress the immune system may be necessary to achieve these results.

Those who don’t recover completely may need to continue on at least a low dose of medication to control the autoimmune attack of PM throughout their lives.


In most cases, the cause of an inflammatory myopathy like polymyositis (PM) is unclear. For some reason, the body’s immune system turns against its own muscles and damages muscle tissue in an autoimmune process.

Viruses might be a trigger for autoimmune myositis. People with the HIV virus, which causes AIDS, can develop a myositis, as can people with a virus called HTLV-1. Some myositis cases have followed infection with the Coxsackie B virus.


As with other muscle diseases, a doctor diagnoses polymyositis (PM) by considering an individual’s history, family medical history and the results of a careful physical examination. This may be followed by some lab tests, perhaps of the electrical activity inside the muscles and usually a muscle biopsy.

Signs and Symptoms

Polymyositis (PM) is more common in females than males and usually begins after age 20. Over a period of weeks or months, several muscles become weak and gradually get weaker. Most affected are the muscles of the hips and thighs, the upper arms, the top part of the back, the shoulder area and the muscles that move the neck.

Many people with PM have pain or tenderness in the affected areas. The person may have trouble extending the knee, stepping down or climbing stairs.


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.



