MPO and granulomatosis with polyangiitis: ANCA, anti-neutrophil cytoplasmic antibody; PR3, anti-proteinase 3; MPO, anti-myeloperoxidase; GPA, granulomatosis with polyangiitis; MPA, microscopic polyangiitis; BVAS, Birmingham Vasculitis Activity Score; VDI, Vasculitis Damage Index; RTX, rituximab; CY, cyclophosphamide; GC, glucocorticoid