DM is a diffuse inflammation of the skin and muscles, with erythema and edema of the skin and weakness, pain and swelling of the muscles, which may be accompanied by arthralgia and damage to multiple organs such as lungs and heart muscles. The etiology and pathogenesis of PM are not yet understood. The diagnosis of poorly dilated esophageal peristalsis and barium retention in the pyriform fossa: skin and muscle are the two main groups of symptoms, with skin often preceding muscle for weeks to years, or with myositis or muscle and skin simultaneously. Skin and muscle symptoms are often not parallel and can be very severe in one and mild in the other. In individual cases, the first organ to show symptoms may not be the skin or muscle, but the heart, lungs or pleura, manifesting as pericardial tamponade, pulmonary fibrosis or pleurisy. 1. Skin symptoms: Typical lesions are edematous purplish spots on both upper eyelids, spreading to the periorbital area and gradually expanding to the face, neck, and upper chest V-zone (Figures 1 to 3). The purplish papules on the extremities of the elbows and knees, especially on the extensor side of the metacarpophalangeal and interphalangeal joints, are accompanied by dilated capillaries, hypopigmentation and covered with fine scales, called Gottron’s sign or Grottron’s papules. Edematous purplish macules on the upper eyelid and Gottron’s sign are important for the diagnosis of DM, especially the former, which appears earliest and is significant for early diagnosis. Other types of skin lesions in DM include heterochromia, erythroderma, cutaneous vasculitis, urticaria, and calcium deposits. There is an increased likelihood of the presence of cutaneous heterochromatosis with malignancy. Cutaneous vasculitis and cutaneous calcium deposits occur mostly in JDM, and those with cutaneous vasculitis are prone to have systemic vasculitis at the same time, often with severe symptoms and poor prognosis when not treated properly. Those with cutaneous calcium deposits tend to have mild damage to important organs and a better prognosis, but there have been reports of extensive calcium deposits in the abdominal wall causing acute abdomen and intra-abdominal hemorrhage. Rarely occurring types of lesions include patchy cutaneous mucin deposits with blistering or maculopapular lesions. Mucin deposits tend to occur in middle-aged and older female patients and can be the first symptom of DM. The prognosis for blisters or herpes is poor. 2, muscle symptoms: involvement of transverse muscle, but the involvement of skeletal muscle is much more common than the myocardium. Smooth muscle is rarely involved. The proximal muscles of the extremities are most vulnerable, such as the deltoid and quadriceps. The onset is mostly symmetrical. The diseased muscles have symptoms such as weakness and pain, and show corresponding motor deficits, such as difficulty in raising the upper limbs, inability to lift the lower limbs and inability to stand up after squatting. In more severe cases, head lifting is difficult and turning over is not possible, showing the involvement of the neck and trunk muscles. In severe cases, the limbs could not be moved in bed or could only move a few centimeters, and even minor muscle contractions could not be seen. The involvement of esophageal and pharyngeal muscles may cause difficulty in swallowing, coughing and choking, and change in pronunciation. Shortness of breath and dyspnea may occur with respiratory muscle involvement. The eye muscles may be involved with diplopia. A small number of patients may not have myalgia and only show muscle weakness. 3. Other system symptoms. Gastrointestinal system: Gastrointestinal symptoms are the most common among the systemic damage, manifested as abdominal distension, decreased appetite, digestion and malabsorption, constipation or diarrhea. Nearly 1/3 of patients have dysphagia, mainly difficulty in swallowing solid food. 2/3 of patients can find abnormalities in barium esophagogram performed in the horizontal position, such as esophageal dilatation, poor peristalsis, slow passage of contrast and retention of barium in the pyriform fossa. jdm can also cause intestinal necrosis due to vasculitis, gastrointestinal ulceration and bleeding. Liver function abnormalities are more common in active disease. Individual patients may have gallbladder sclerosis and cholestatic hepatitis, when anti-mitochondrial antibodies can be detected.