Polymyositis and dermatomyositis are connective tissue disorders that affect tendons, ligaments, and the dense collagen-based tissue covering the ends of muscles. Swelling and tenderness of the muscles (polymyositis) and, in some cases, the skin (dermatomyositis) are symptoms of these diseases. Arms and legs become weak as a result of the disease.
Cardiovascular complications are a leading cause of death in myositis. Despite this, cardiac involvement in polymyositis and dermatomyositis is uncommon clinically.