The vascular response is central to the inflammatory process. How is diffuse erythema of the skin diagnosed? Early dermatomyositis: The skin damage is often on the entire facial skin, including the forehead, cheeks, cheekbones, ears and chin, in addition to the eyelids, showing diffuse redness and swelling, with no normal skin visible on the entire face. At this time, with a finger gently press the red and swollen skin on the face, there is a soft and hard feeling like pressing on a rubber block. Cosmetic allergy caused by solar dermatitis: although the facial skin is also red and swollen, but under close observation, the redness is limited to the two sides of the cheeks, chin, erythema edges are clear, the face can be seen a lot of normal color skin, at this time, such as gently pressing the skin with a finger at the red and swollen place, there is a soft sense of feeling as if pressed on the cotton. 1.Systemic erythema Lupus lesions with zygomatic cheek edema butterfly-shaped erythema, dark erythema on the extensor surfaces of fingers (toes) joints and peri-nail-centered edematous purple erythema, purple erythema on the extensor surfaces of interphalangeal joints and metacarpal joints (toes) joints as well as stiff capillary dilatation of erythema on the nail root folds make a difference, and the renal involvement is the major factor in the multisystemic lesions in SLE, while dermatomyositis is dominated by the proximal muscles of the limbs involved, and hoarseness of voice and phagocytic difficulties are also common. Dumbness and dysphagia are also common. In addition, serum myoplasmic enzyme and urinary creatine excretion are significantly higher in patients with dermatomyositis, and electromyography and muscle biopsy can be used for differentiation when needed. 2, systemic scleroderma dermatomyositis late lesions such as skin sclerosis, subcutaneous adipose tissue calcium deposits, histology can also be seen in connective tissue swelling, sclerosis, atrophy near the skin, etc., but in the early stage of systemic scleroderma, Raynaud’s phenomenon, facial and limb end swelling, sclerosis and later atrophy for its characteristics, muscle lesions dermatomyositis early lesions has been significant for substantial myositis, while in systemic scleroderma muscle lesions usually have a significant increase in serum plasma enzymes and urinary creatine excretion measurements, when needed, electromyography and muscle biopsy can differentiate. In systemic scleroderma, muscle lesions usually appear in the late stage and can be distinguished from interstitial myositis.