Myositis.

Symptoms

Symptoms

We do not know what causes myositis. But because myositis has many forms, it probably has many causes. Some scientists think that myositis results when a person with a certain genetic background is exposed to particular chemicals, viruses, or other infectious agents.

Whatever triggers these diseases also results in abnormalities in the immune system. The immune system consists of groups of cells called lymphocytes that circulate throughout the body. In healthy people, these lymphocytes act as a defense force that produces substances that attack viruses, bacteria, and other agents of disease. But in many people with myositis, there is an abnormality in the immune system that results in the production of proteins called autoantibodies. Autoantibodies and some of the lymphocytes turn against the body's own tissues and may cause damage.

Because illnesses associated with autoantibodies are called autoimmune diseases, many doctors consider myositis to be an autoimmune disease. Some autoantibodies found in people with myositis are found in other autoimmune diseases, but a few special ones are only found in people with myositis. These are called myositis-specific autoantibodies. They seem to be useful in helping doctors predict the problems that some people might develop and how they might respond to treatment.

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