What are the possible complications of polymyositis and dermatomyositis?
In a few cases drug treatment doesn’t work fully and your muscles can remain weak. It's not yet clear why this happens, but moderate exercise (so you start breathing faster but aren’t straining yourself) will still help to improve muscle strength.
Occasionally polymyositis can also affect breathing and swallowing. This may happen at the start of severe cases, when the muscles used become very weak. It may also cause weakening of your heart, and inflammation of your lungs may cause scarring. This affects how your lungs work. Lung and heart conditions can cause long-term breathlessness.
Children with dermatomyositis may develop painful calcium deposits in damaged muscles. These deposits, combined with immobility, can occasionally result in the joints becoming permanently bent (flexion contracture).
Polymyositis occasionally occurs in people who also have another autoimmune disease such as rheumatoid arthritis, lupus and scleroderma.
On rare occasions, myositis can be associated with cancer. Most people with polymyositis and dermatomyositis don’t develop cancer, but your doctor might arrange tests such as a chest x-ray or an ultrasound scan of your abdomen and pelvis to be on the safe side.