The most typical clinical manifestations of myositis are muscle weakness and myalgia. Myositis usually has a relatively insidious onset, and only a few patients will have subacute or acute symptoms, such as fever, decreased appetite, weight loss, etc. The first muscles involved in myositis are usually the limb girdle muscles, proximal limb muscles, neck muscles, especially the pelvic girdle muscles, and lower limb muscles, which usually manifest as difficulty in squatting, going up and down stairs, raising arms, and dressing. If the condition is severe, it may also manifest as limited turning, difficulty in swallowing and breathing. If myositis is not effectively controlled, it can also involve the organs and cause damage to the digestive tract, lungs, and heart, which can manifest as interstitial pneumonia, myocarditis, cardiac arrhythmia, etc.