Polymyositis (pol-e-my-o-SY-tis) is a condition in which swelling and irritation, called inflammation, happens when the immune system attacks its own muscle tissues. Polymyositis causes weakness of the muscles involved in body movement, called skeletal muscles. Muscle weakness most often happens on both sides of the body at the same time.
The condition, also called an autoimmune condition, isn’t common. Having this condition can make it hard to climb stairs, rise from sitting, lift objects or reach up.
Polymyositis most often affects adults in their 40s to 60s. Symptoms tend to come on slowly, over weeks or months.
There’s no cure for polymyositis. But treatment can improve muscle strength and help muscles work better. Treatments include medicines and physical therapy.
