May is ALS Awareness Month. Learn more about what you can do to end ALS with MDA.

An icon that marks all of our informational disease pages

Polymyositis (PM)


In most cases, the cause of the idiopathic inflammatory myopathies (IIM), the disease group that encompasses polymyositis (PM), is unclear. For some reason, the body’s immune system turns against its own tissues 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 IIM will develop. A combination of genetic, immune, and environmental factors is thought to contribute to development of the IIMs. Some environmental triggers that have been associated with IIMs include viral infection and certain medications.


  1. Findlay AR, Goyal NA, Mozaffar T. An overview of polymyositis and dermatomyositis. Muscle Nerve. 2015;51(5):638-656. doi:10.1002/MUS.24566
  2. Baig S, Paik JJ. Inflammatory muscle disease – An update. Best Pract Res Clin Rheumatol. 2020;34(1):101484. doi:10.1016/j.berh.2019.101484

Last update: Feb 2023
Reviewed by Julie Paik, MD, MHS; Johns Hopkins University

Looking for more information, support or ways to get involved?

Find MDA
in your Community