Reticulocyanosis is a skin spasmodic disorder that is a skin manifestation of certain diseases, and can occur in some normal people in cold environments. Gangrene is a specific morphological change such as black or dark green coloration after tissue necrosis due to secondary infection by putrefactive bacteria and other factors. Both are seen together in the skin lesions of polyarteritis nodosa. Nodular polyarteritis, also known as periarteritis nodosa and necrotizing arteritis and polyarteritis, is a fatal disease. It is a fatal disease with a fast-developing clinical course and a wide range of lesions, usually involving the arterial system throughout the body. The clinical manifestations are complex and varied, and vary according to the site or organ involved in the lesion. Because the symptoms involve several different systems, this disease can also be misdiagnosed as other similar diseases, such as skin, respiratory tract, heart, central nervous system or urinary tract diseases. 1, heavy allergic purpura The symptoms of this disease and nodular polyarteritis are very similar, but there are differences: ① Purpura cases of rash in the lower extremities, and more transient, while nodular arteritis rash often involves the whole body, a longer period of time. The abdominal symptoms are more severe in the former and less severe in the latter. ③ The prognosis of the former is not as serious as that of the latter. 2.Chronic nephritis Due to the abnormalities seen in urine, hypertension and sometimes an increase in blood urea nitrogen, nodular polyarteritis is often misdiagnosed as simple chronic nephritis, and it is advisable to pay attention to it. Pulmonary hemorrhagic nephritis syndrome is characterized by hemoptysis, anemia, and nephritis, often with fever, cough, and dyspnea, and rhonchi may be heard on auscultation. Sputum smear examination can see macrophages, containing ferritin. It is easily complicated by azotemia and renal failure. Prognosis is serious. Adrenocorticotropic hormone and antimetabolites can be tried. Focal or diffuse glomerulonephritis and intra-alveolar hemorrhage are the main lesions of this disease. 3.Multiple aortitis (pulselessness) Hypertension is the prominent clinical manifestation. If there are also symptoms of aortic occlusion, fever, rash, arthritis, or increased blood sedimentation rate, this disease should be considered. 4.Systemic lupus erythematosus (SLE) Most of them have renal injury, which should be differentiated from nodular polyarteritis, but SLE is mostly seen in girls, with typical rash, positive antinuclear antibody and lupus cell test, which can be differentiated. 5, Kawasaki disease, also known as cutaneous mucocutaneous lymph node syndrome, first reported in Japan, is an acute febrile rash disease of unknown etiology, common in infants and young children, and its main clinical features are persistent fever, polymorphic erythema of the skin, congestion of the mucous membranes of the oral cavity, congestion of the conjunctiva of the two eyes, swelling of the hands and feet, and swelling of the cervical lymph nodes, and there is often coronary artery damage. Kawasaki disease is similar to infantile polyarteritis nodosa, but the former is a self-limiting disease with a better prognosis. The most common early manifestations are unexplained fever, hypertension, acute abdominal pain, glomerulonephritis, insufficient coronary blood supply, peripheral neuropathy and muscle and joint lesions. There may be no local symptoms or only limited skin lesions. According to the involvement of tissues and organs, nodular polyarteritis is clinically classified into systemic (systemic) and limited types.