Dermatomyositis, also known as cutaneous heterochromic dermatomyositis, is an autoimmune connective tissue disease that involves mainly the transverse muscles and is a non-purulent inflammatory lesion with a lymphocytic infiltrate that may or may not be associated with multiple skin lesions or with various visceral lesions. Polymyositis refers to this group of disorders without skin lesions. The clinical manifestations can occur at any age, with a slight female predominance. Some cases are preceded by symptoms such as irregular fever, Raynaud’s phenomenon, arthralgia, headache, anxiety, and fatigue. The onset of the disease is mostly slow, with a few cases having an acute or subacute onset. Muscle and skin are the two main groups of symptoms of the disease, the skin lesions often precede the muscle for several weeks to years, a few have myopathy first, followed by skin lesions, some patients have muscle and skin at the same time. 1, muscle symptoms usually involves transverse muscle, sometimes smooth muscle and cardiac muscle can also be involved. Any part of the muscle can be invaded, but often the muscles of the limbs are the first to be affected, and the proximal muscles of the liver are more vulnerable than the distal ones. The muscles of the scapular and pelvic girdles are usually the first to be affected, followed by the upper arm and femoral muscles, and to a lesser extent the muscles of other areas. The lesions are often symmetrical, and in a few cases the damage can be limited to one limb muscle group, or a single muscle or many muscles in succession, one after the other; usually the patient feels weakness, followed by muscle pain, pressing pain and motor pain; and then various motor dysfunctions and specific postures due to decreased muscle strength. The symptoms may vary depending on the number, severity, and location of the muscle lesions, and usually include difficulty in raising the arms, head movement, or standing up after squatting, and poor gait. When the pharynx, upper esophagus and palate muscles are involved, hoarseness and difficulty in swallowing may occur; when the diaphragm and intercostal muscles are involved, shortness of breath and difficulty in breathing may occur; when the heart muscles are involved, heart failure may occur; when the eye muscles are involved, diplopia may occur. 2, skin symptoms The skin lesions of this disease are diverse, some are the first symptoms; some are specific and helpful for diagnosis; some appear to suggest concomitant visceral malignancy; some are related to prognosis. The lesions are often not parallel to the degree of muscle involvement, sometimes the lesions can be more extensive with only mild myositis, and conversely there are severe muscle lesions with only mild lesions, sometimes the lesions reflect the degree of muscle lesions. The lesions are usually purplish on the face, especially on the upper eyelids, and gradually expand diffusely to the forehead, cheek, preauricular, neck, and upper chest V-zones, as well as the scalp and postauricular region. Dendritic capillaries are clearly dilated near the lid margin of the closed eye, and occasionally capillaries with pinhead-sized petechiae at the tip of the bend are seen; the periorbital puffy purplish-red patches centered on the eyelid are characteristic. The appearance of purple-red papules and spots on the extensor surfaces of the elbows and knees, especially the metacarpophalangeal and interphalangeal joints, which later become atrophic, with capillary dilation, hypopigmentation and fine scales overlying, and occasionally ulceration, called Gottron’s sign, is also characteristic, and rigid capillary dilation and petechiae can be seen in the nail root crease, which helps in the diagnosis. In some cases, the rash may also appear on the trunk as diffuse or limited dark red spots or papules on the skin of the anterior sternum or between the scapular muscles or the lower back, usually without pruritus, pain, or sensory abnormalities, but in a few cases there may be severe itching, and the damage is transient, recurrent, and then fuses with each other and persists, covered with fine scales, and the oral mucosa also appears erythematous.