Reticular cyanosis is a skin spasmosis, a skin manifestation of certain diseases, and some normal people also develop reticular cyanosis in cold environments. Gangrene is a specific morphologic change of black and dark green color due to secondary infection by spoilage bacteria and other factors after tissue necrosis. Both are seen together in the skin lesions of polyarteritis nodosa. Polyarteritis nodosa, also known as periarteritis nodosa and necrotizing arteritis, polyarteritis, etc., is a fatal disease. The clinical course is rapid and extensive, usually involving the systemic arterial system, and the clinical manifestations are complex and variable, depending on the site or organ involved. Polyarteritis nodosa belongs to a variety of conditions in TCM because of its diverse clinical manifestations. It is believed to be closely related to fire, heat, phlegm and blood stagnation, which ultimately leads to obstruction of blood vessels and veins, Qi and blood stagnation, and blood stagnation and paralysis. Many sources have found that viral infections are closely related to polyarteritis nodosa. 30% to 50% of patients with hepatitis B virus infection, hepatitis B surface antibody (HTLV-1), human immunodeficiency virus (HIV), etc. may be associated with vasculitis. Immune complexes formed by viral antigens and antibodies are deposited in the vessel wall, causing necrotizing arteritis. Drugs such as sulfonamides, penicillin, etc., as well as after serum injection can also be the cause of this disease, and tumor antibodies can induce immune complexes leading to vasculitis. A few patients with hairy cell leukemia develop this disease after the disease, and cutaneous nodular polyarteritis has been reported in association with segmental ileitis. In conclusion, the etiology of this disease is multifactorial and its development is associated with immune dysregulation. The above factors lead to vascular endothelial cell damage, releasing a large number of chemokines and cytokines, such as interleukin (IL-1) and tumor necrosis factor (TNF), which aggravate endothelial cell damage, and anti-neutrophil plasma antibodies (ANCA), which can also damage the vascular endothelium, causing loss of vascular regulating ability, vascular spasm, ischemic changes, thrombosis and vascular obstruction.