The outlook varies, depending on the type of myositis.
Idiopathic inflammatory myopathies. With proper treatment, most people with polymyositis or dermatomyositis eventually regain at least some muscle strength. Often, muscle strength returns to normal. Typically, inclusion body myositis does not improve with treatment. However, the illness usually progresses slowly and does not affect a person's lifespan unless complications lead to serious illness, such as pneumonia caused by swallowing or breathing problems. Eventually, some patients need a cane to help them walk. Others require a wheelchair. If a person with dermatomyositis develops cancer, the prognosis may be worse. Medications taken to treat these muscle diseases may cause complications that affect prognosis. For example, serious infections may complicate the use of immune suppressing medications.
Infectious myositis. Once the flu passes, muscle symptoms improve. Treatment usually is effective, although recovery can be slow in people with trichinosis. For pyomyositis, the prognosis is good if the infection is treated promptly. If not, the infection can pass into the bloodstream and spread throughout the body.
Benign acute myositis. Children typically walk normally again within a few days.
Myositis ossificans. The prognosis is very good. If the bony lump does not disappear on its own, your doctor may recommend surgery to remove it.
Drug-induced myositis. The prognosis is very good. In most cases, symptoms subside when the drug is stopped.