What is myositis?
Myositis is the general term for swelling of the muscles. Injury, infection, certain medicines and even exercise can cause muscle swelling. The swelling will go away once the injury or infection is treated, once you rest your muscles from exercise, or once you stop taking the medicine.

Often people who have temporary myositis from one of these causes are concerned when they find the TMA web site and read about the serious, chronic form of myositis. When we talk about myositis, we mean the inflammatory myopathies.

What are inflammatory myopathies?
Myositis is the popular term used to describe a number of inflammatory myopathies:

• dermatomyositis (DM)
• inclusion-body myositis (IBM)
• juvenile forms of myositis (JM)
• polymyositis (PM)

These diseases cause swelling and loss of muscle. They are also called idiopathic inflammatory myopathies. “Idiopathic” means the causes are unknown.

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.

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
  

For more specific signs and symptoms, click the different disease types listed above.

Updated March 2007