The antineutrophilic cytoplasmic autoantibody (ANCA)-associated vasculitides (AAV) are comprised of Granulomatosis with Polyangiitis (GPA, formerly Wegener’s Granulomatosis), Microscopic Polyangiitis (MPA) and Eosinophilic Granulomatosis with Polyangiitis (EGPA, formerly Churg-Strauss Syndrome). They share the features of small vessel vasculitis but are otherwise a heterogeneous group with different preferences of organ involvement and frequency of ANCA positivity.

In general, GPA and EGPA are characterized by granulomatous lesions (especially of the respiratory tract) and small- to medium-size vessel vasculitis in biopsy specimens, whereas MPA is a small- to medium-size vessel vasculitis without granuloma. Protease proteinase 3 (PR3) and myeloperoxidase (MPO) ANCA are present in almost all patients with MPA and GPA in the active generalized stage of the disease; in EGPA, ANCA are present in less than 40 percent and their presence is associated with typical vasculitis manifestations such as glomerulonephritis.¹

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