What are the characteristics of skin damage caused by rheumatic diseases?

There are two typical rashes: ① purple-red spots around the orbit, mostly located in the upper eyelid, which can appear on one side or both sides for the first time; Acute onset is obviously swollen and not concave, and chronic onset is not obvious. This rash gradually spread to the forehead, cheekbones, ears, neck and upper chest "V" area, scalp and behind the ears can also be involved. This kind of eyelid-centered purplish red staining of edema around the orbit is often the characteristic of dermatomyositis diagnosis. ② Another characteristic skin lesion is located on the joint extension surface, such as the metacarpophalangeal joint extension surface and the proximal interphalangeal joint. Polygonal flat or purple millet-to-rice-sized papules and spots appear on the extension surface of elbow joint and knee joint or the inside and outside carina of ankle joint, and then gradually shrink, and the capillaries of the upper complex are dilated, hypopigmentation and scaly, with occasional surface damage, which is called "Gao Xue sign". In addition to the above two characteristic rashes, there is also a heterochromic rash. The lesions are multiple keratopapules, mottled pigmentation and telangiectasia, which can be confined to the "V" area of the upper chest or multiple places. Another nail root fold can be seen in the thickening of nail skin, dark red spots and stiff capillary dilatation, which is also helpful for diagnosis. On the basis of heterochromic lesions, there are occasional bright red, fiery red or brownish red systemic plaques, which are slightly swollen and look like drunkenness, accompanied by more dark brown or grayish brown needle-cap-shaped large pigment spots, and a large number of capillaries are coiled or branched. This kind of skin lesion often suggests malignant tumor, which is called malignant erythema. Dermatomyositis rash usually has no conscious symptoms, and a few patients have severe itching. Most patients' rashes are light-sensitive, that is, they get worse after illumination, and the rashes can recur.