Polymyositis

Polymyositis is a group of diffuse inflammatory muscle diseases of unknown etiology, with main clinical manifestations characterized by symmetric proximal limb muscle weakness, neck muscle weakness, pharyngeal muscle weakness, muscle tenderness, and elevated serum enzymes. Most scholars believe that this disease is related to autoimmune disorders. Some scholars also consider it to be associated with viral infections or genetic factors. The onset is mostly subacute, and it can occur at any age, with a higher prevalence in women aged 20-40. Some patients may have a history of infection before onset, with symmetric proximal limb muscle weakness, pain, and tenderness as the main signs. It can involve the pharyngeal muscles, respiratory muscles, and neck muscles. Muscle atrophy may occur in the late stage. Some cases may be complicated by skin or visceral involvement, or malignant tumors. Some patients have malignant tumors before onset, and approximately 20% of patients are complicated by other autoimmune diseases such as systemic lupus erythematosus, scleroderma, rheumatoid arthritis, and Sjögren's syndrome. Due to differences in the extent of involvement and associated conditions, the clinical manifestations of this disease are diverse. Usually, the disease reaches its peak within weeks to months, with generalized muscle weakness; in severe cases, respiratory muscle weakness can be life-threatening. Therefore, early diagnosis and treatment are very important. As long as hormones or immunosuppressants are applied promptly, the prognosis of simple polymyositis can be expected to be good, while those complicated by malignant tumors and multiple connective tissue diseases have a poorer prognosis.