Reticulocutaneous cyanosis is a skin spasm, a cutaneous manifestation of certain diseases, and some normal people also develop reticulocutaneous 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 of the disease is fast developing and extensive, usually involving the systemic arterial system. The clinical manifestations are complex and variable, varying according to the site or organ involved. The presence of both reticular cyanosis and gangrene can be seen in polyarteritis nodosa. The causes of polyarteritis nodosa are not well understood, but are generally considered to be related to the following factors: 1. immune complexes: according to research, in some patients with hepatitis B combined with this disease, the hepatitis B virus and the immune complexes formed by it, play an important role in the development of the disease. 2. 2, allergic factors: Some scholars believe that allergy to drugs such as penicillin, sulfonamide and injected serum is also the cause of the disease. The occurrence of the disease can be caused by a variety of reasons, and its pathogenesis is related to the dysregulation of immune mechanisms, as described by various authors. The disease belongs to the category of various diseases in TCM because of its diverse clinical manifestations. It is believed to be closely related to fire and heat, phlegm and blood stagnation, which ultimately leads to obstruction of blood vessels and veins, Qi and blood stagnation, and blood stagnation and paralysis.