AbstractA 76‐year‐old man was admitted with general fatigue, weight loss, fever, headache, renal failure, and a high serum level of myeloperoxidase‐antineutrophil cytoplasmic antibody. Biopsy revealed citrullinated histone H3 (citH3)‐positive neutrophils adherent to the temporal artery endothelium. Three days after completing pulse steroid therapy, he suffered from a sudden disturbance of consciousness and died. On autopsy, the kidneys showed the most severe vasculitis with dense infiltration of citH3‐positive neutrophils. The lungs showed intra‐alveolar hemorrhage due to capillaritis. Severe brain hemorrhage was found in the left frontal lobe and putamen with uncal herniation. No vasculitis or thrombi was observed in the brain. The right dura mater was thickened due to fibrosis and inflammation. In conclusion, autopsy revealed systemic vasculitis with infiltration of abundant citH3‐positive neutrophils, suggesting that the neutrophil extracellular trap formation and citH3 might play important roles in the early phases and development of microscopic polyangiitis.