ANCA vasculitis: to lump or split?

Abstract

Why we should study MPA and GPA separatelyThe three types of vasculitis associated with ANCA [ANCA-associated vasculitis (AAV)] are granulomatosis with polyangiitis (Wegener’s) (GPA), microscopic polyangiitis (MPA) and eosinophilic granulomatosis with polyangiitis (Churg–Strauss syndrome) (EGPA). They have been classified together in the majority of classification systems published since the introduction of ANCA, including the most recent 2012 Chapel Hill classification system [1]. GPA and MPA have been considered together in clinical and treatment studies because they share many clinical features: for example, renal involvement is identical in both diseases with a pauci immune focal segmental necrotizing glomerulonephritis. Granulomatous involvement, particularly of the upper respiratory tract, is a characteristic feature of GPA, but not of MPA; eosinophilia, asthma and atopy typically occur in EGPA. More than 90% of GPA and MPA patients are ANCA positive. In most European studies, the ANCA antigen specificity of GPA is predominantly proteinase 3 (PR3), and in MPA is predominantly myeloperoxidase (MPO). Only 50% of EGPA patients are ANCA positive, mostly MPO. GPA and MPA are traditionally treated in the same way with glucocorticoids and immunosuppressive drugs.