Polymyositis

Polymyositis is a rare autoimmune disease that makes your immune system attack your muscles.

It’s a type of myositis. Myositis causes chronic inflammation in your muscles — swelling that comes and goes over a long time. Eventually, this inflammation makes your muscles feel weak.

If you have polymyositis, you may have inflammation in multiple muscles at the same time. It usually affects the muscles on or near the center of your body, including in your:

Arms.
Hips and thighs.
Chest.
Back.
Abdomen.
Neck.

Experts aren’t certain what causes polymyositis, and there’s no cure for it. A healthcare provider will treat the symptoms you’re experiencing and suggest ways to manage how much they affect your daily routine.