The length of time a patient with myositis can live cannot be generalized and is related to the severity of the patient’s condition. In general, the disease usually does not affect life expectancy if the patient does not develop organ damage and receives regular hospital treatment; however, if the patient is older and has combined organ damage, the prognosis is poor. Myositis is an inflammatory disease of the skeletal muscles caused by multiple etiologies, with acute or subacute onset and a history of hypothermia or cold before the disease. The main manifestation is muscle weakness with pain mainly in the proximal extremities. Hormonal therapy is effective in most patients, and when hormonal therapy is unsatisfactory, immunosuppressive agents or immunoglobulins may be added to the treatment. Most patients can be cured by regular treatment. However, some patients with repeated episodes of muscle pain and without formal treatment may develop major organ lesions, such as pulmonary fibrosis and abnormal thyroid function, etc. The prognosis for such patients is poor, especially for elderly patients with combined tumors that can affect their life expectancy. In conclusion, the approximate life expectancy of myositis varies from person to person, and it is recommended that it must be treated actively to prevent serious complications, which in turn can affect life expectancy. Daily rest and physical exercise under the guidance of a doctor and a balanced and nutritious diet can help promote recovery.