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. The clinical manifestations are complex and variable, varying depending on the site or organ involved. What are the tests for polyarteritis nodosa? The total number of white blood cells and neutrophils are often increased, and there may be varying degrees of anemia due to blood loss or renal insufficiency. Immunological examination of gammaglobulin, total complement and C3 complement level decrease often reflect the active stage of the disease, rheumatoid factor, anti-nuclear antibody is positive or low titer positive, ANCA may occasionally be positive, about 30% of cases can be measured positive HBsAg. 3, pathological biopsy is important for diagnosis. However, the lesions are segmentally distributed, and it is vital to select the appropriate organ, site for biopsy, which can be seen in small and medium-sized arterial necrotizing vasculitis. If biopsy is difficult or the results are negative, angiography can be performed. Aneurysmal dilatation or segmental stenosis of small and medium-sized arteries in the kidney, liver, mesentery, and other internal organs are often found and are valuable in the diagnosis of the disease. The most common early manifestations are fever of unknown origin, hypertension, acute abdominal pain, glomerulonephritis, inadequate coronary artery supply, peripheral neuropathy and muscle and joint lesions. Nodular polyarteritis is clinically classified into two types: systemic (systemic) and limited, depending on the involvement of tissues and organs.