ANCA-associated vasculitides (AAV) are necrotizing vasculitis, with few or no immune deposit, predominantly affecting small vessels. Among AAV, granulomatosis with polyangiitis (GPA) is characterized by granulomatous necrotizing vasculitis with the upper and lower respiratory tract involvement, eosinophilic granulomatosis with polyangiitis (EGPA) is characterized by eosinophil-rich and necrotizing granulomatous inflammation with asthma and eosinophilia, and microscopic polyangiitis (MPA) is characterized by necrotizing arteritis with glomerulonephritis and pulmonary capillaritis.
