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 of the disease is rapid and extensive, usually involving the systemic arterial system, with complex and variable clinical manifestations that vary according to the site or organ involved. The most common early manifestations are fever of unknown origin, hypertension, acute abdominal pain, glomerulonephritis, coronary artery insufficiency, peripheral neuropathy, and muscle and joint lesions. Nodular polyarteritis is clinically classified into two types: systemic (systemic) and limited, based on the involvement of tissues and organs. The cutaneous type is mainly based on the manifestation of skin lesions, especially subcutaneous nodules distributed along superficial arteries, polymorphic lesions, and skin biopsy can make a clear diagnosis if necessary. The systemic type has no uniform criteria for diagnosis because of the extensive involvement of the system and multiple clinical manifestations. ③Can exclude testicular pain or pressure pain due to infection, trauma or other causes. ④Myalgia, weakness or tenderness in the lower limbs. ⑤ Mononeuritis or polyneuropathy. ⑥Diastolic blood pressure ≥ 12.0kPa (90mmHg). (vii) Elevated creatinine urea nitrogen level. ⑧HBsAg or HBsAb(+). ⑨Arteriography shows visceral artery infarction or aneurysm formation. (Excluding arteriosclerosis, myofibrillar dysplasia or other non-inflammatory causes.) ⑩Small and medium artery biopsy shows granulocytes or with mononuclear cell infiltration in the arterial wall. Those with at least 3 positive of the above 10 may be considered to have nodular polyarteritis. The biopsy and angiographic abnormalities are important diagnostic factors.