Polymyositis (PM) is more common in females than males and
usually begins after age 20. Over a period of weeks or months,
several muscles become weak and gradually get weaker. Most
affected are the muscles of the hips and thighs, the upper arms,
the top part of the back, the shoulder area and the muscles that
move the neck. Many people with PM have pain or tenderness in
the affected areas. The person may have trouble extending the
knee, stepping down or climbing stairs. Lifting things, fixing
the hair or putting things on a high shelf may be difficult. It
can be hard to raise the head off the bed when lying down. PM
also can affect the heart muscle, causing a condition called
inflammatory cardiomyopathy. The muscles involved in breathing
may be affected and a few people develop some inflammation of
the lung tissues themselves, another respiratory complication.
Of course, the heart, respiratory and swallowing problems are
the most serious effects of PM and need close monitoring.