Polymyositis
Definition
Polymyositis (PM) is an inflammatory muscle disease with an unknown cause. The disease has a gradual onset and generally begins in the second decade of life and, thus, it rarely affects persons under the age of 18. It causes muscles to exhibit varying degrees of decreased strength, usually affecting those muscles that are closest to the trunk of the body. Trouble with swallowing (dysphagia) may occur with polymyositis.
Description
In polymyositis, muscles exhibit varying degrees of weakness, evolving gradually over weeks to months. It is known that PM begins when white blood cells, the immune cells of inflammation, spontaneously invade muscles, and is thus termed an autoimmune disease. In PM, muscle fibers are found to be in varying stages of necrosis (tissue death) and regeneration. The muscles affected are typically those closest to the trunk or torso, resulting in weakness that can be severe....
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