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.