What is myositis?
Myositis means muscle inflammation, and can be caused by infection, injury, certain medicines, exercise, and chronic disease. Some of the chronic, or persistent, forms are idiopathic inflammatory myopathies, and those are the diseases we discuss here. "Idiopathic" means that the cause is unknown.
What are inflammatory myopathies?
The inflammatory myopathies are a group of diseases that involve chronic muscle inflammation, accompanied by weakness:
- dermatomyositis (DM)
- inclusion-body myositis (IBM)
- juvenile forms of myositis (JM)
- polymyositis (PM)
Recent research notes that there are other ways to classify myositis types based on both laboratory and clinical differences. For instance, myositis can be associated with cancer, or it may involve the skin only, or it may be one of several diseases affecting a patient. It's important to know that these diseases are systemic, meaning they affect other systems besides the muscles.
Inflammatory myopathies are thought to be autoimmune diseases, meaning the body's immune system, which normally fights infections and viruses, is misdirected and attacks the body's own normal, healthy tissue through inflammation, or swelling. All of these diseases can cause muscle weakness, but each type is different. Learn more about autoimmunity.
Educate yourself and others with TMA publications
Myositis 101. Learn the facts about a complicated and poorly-understood disease. TMA has published an introductory brochure that will help you understand the symptoms, treatment and complications of myositis. For your free copy, or to arrange for more than one copy for an awareness campaign, email
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Signs and symptoms:
- Muscle weakness, sometimes with muscle pain
- General tiredness and fatigue
- Trouble climbing stairs, standing from a seated position, or reaching up
- Difficulty swallowing or breathing
- Rash on knuckles, chest, face and back
- Persistent dry cough
For more specific signs and symptoms, click the different disease types listed above.
Updated October 2014