Granuloma annulare is a benign inflammatory skin lesion of unknown etiology that occurs in the dermis or subcutaneous tissue and is characterized by annular papules or nodular lesions. Etiology and pathogenesis】 The etiology is unknown and may be related to trauma, insect bites, sun exposure, pressure, drugs, and viral infections. Anti-thyroid antibodies have been measured in the blood of patients with disseminated granuloma annulare, and other immunological methods such as direct immunofluorescence and macrophage inhibition tests have been studied, suggesting that delayed metaplasia plays an important role in the pathogenesis, but the nature of the antigen is unclear; IgM and C3 deposition at the junction of the vessel wall and epidermis dermis have been detected with fluorescent antibodies, suggesting that the disease is related to vasculitis. The relationship between granuloma annulare and diabetes mellitus has been studied extensively. 21% of patients with disseminated granuloma annulare and 10% of patients with limited granuloma annulare have diabetes mellitus, and some patients with insulin-dependent diabetes mellitus and limited granuloma annulare have increased HLA-B8 detection rate, and some patients with granuloma annulare have increased HLA-A31 and B35. Clinical manifestations】 Children and young people are more affected, and women are two to three times more affected than men. The preferred site is the extensor side of the distal extremities, with the dorsum of the hand and forearm being particularly common, and any part of the body can be involved except the mucosa. The typical lesions start as small, smooth, hard papules, which can be normal-skinned, light red or purple, and gradually recede in the center of the lesion and become circumscribed, runner-shaped or bow-shaped, with a diameter of 1 cm to 5 cm, sometimes larger, and one or several in number; there is no conscious manifestation, and sometimes there is mild pruritus. The disease is generally self-limiting, most of them are naturally absorbed within 2 years, some can be up to 25 years, the disease has a high recurrence rate, 40% of patients recur in the original place, but the recurrent lesions fade faster. In addition to the above-mentioned typical lesions, there are also the following special clinical types: 1. giant granuloma annulare: solitary, deeper infiltration, persistent annular erythema or annular flat moss-like changes. 2. Subcutaneous nodular granuloma annulare: it is found on the lower extremities and buttocks, mostly in children, with deeper infiltration and purplish or reddish subcutaneous nodules, but ulcers may occur in the center of the nodules. 3, penetrating granuloma annulare: most likely on the back of the hands and limbs, the central lesions are often umbilical concave, like infectious molluscum contagiosum-like lesions, seasonally related, can be aggravated in summer. 4. Disseminated granuloma annulare: It occurs on the wrist, forearm, and sometimes all over the body, but does not involve the scalp and palmoplantar, mostly as 1mm to 2mm sized, skin-colored, round papules, which can be isolated or fused into patches. In addition, granuloma annulare can occur in AIDS patients at any stage of the disease, with typical and mostly disseminated granuloma annulare (60%) and limited granuloma annulare in only 40%. Histopathology】 The basic pathology is focal collagen fiber degeneration, inflammatory reaction and fibrosis, the lesions can be in the upper and middle dermis, and can also involve the deep dermis and subcutaneous tissue, collagen fiber degeneration can have incomplete degeneration of small lesions and complete degeneration of large lesions, surrounded by fenestrated inflammatory cells. Diagnosis and differential diagnosis】 Since there are many clinical types of granuloma annulare, the diagnosis must be determined by combining with pathology. The disease should be differentiated from lipoid progressive necrosis, nodular disease, tinea corporis, lichen planus, persistent elevated erythema, and infectious molluscum contagiosum.