Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitides (AAVs) are a heterogeneous group of inflammatory diseases that includes granulomatosis with polyangiitis (GPA, Wegener’s granulomatosis), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (EGPA, Churg-Strauss syndrome), and is characterized by small vessel necrotizing vasculitis and the presence of autoantibodies targeting either proteinase 3 (PR3) or myeloperoxidase (MPO). Here, MPO is linked to microscopic polyangiitis.