Clinical features of ANCA-associated vasculitis

The primary ANCA-associated vasculitides are granulomatosis with polyangiitis (Wegener's, GPA), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (EGPA, Churg-Strauss syndrome, CSS). They predominantly affect small (and medium-sized) vessels and share a variable association with ANCA (anti-neutrophil cytoplasm antibody) directed against neutrophil proteinase 3 (PR3, mainly in GPA) and myeloperoxidase (MPO, mainly in MPA and CSS). Crescentic necrotizing glomerulonephritis and alveolar haemorrhage due to pulmonary capillaritis represent classical (vasculitic) organ manifestations of the ANCA-associated vasculitides (AAV). MPA occurs as a 'pure' small (to medium-size) vessel vasculitis, whereas GPA and CSS are characterized by additional distinct clinical and pathological features. In GPA, granulomatous lesions of the upper and/or lower respiratory tract are a hallmark of the disease. Granulomatous lesions may be large in appearance and occur as space-consuming, infiltrating, and destructive inflammatory masses. GPA is believed to follow a stagewise course with an initial localized form, restricted granulomatous lesions of the upper and/or lower respiratory tract without clinical signs of vasculitis, and a consecutive generalization to systemic vasculitis which may be either non-organ-threatening (early systemic) or organ- and life- threatening (generalized GPA). Rarely, patients arrest in the localized stage and do not progress to systemic disease. In EGPA asthma, hypereosinophilia and eosinophilic organ infiltration (e.g. eosinophilic myocarditis) are typical features of the disease apart from vasculitis. Similarly to GPA, EGPA follows a stagewise course: asthma and eosinophilia may precede full-blown disease for several months or years. Recent cohort studies suggest different phenotypes in EGPA (predominantly vasculitic and MPO-ANCA-positive and predominantly with eosinophilic organ infiltration, usually ANCA-negative). This chapter focuses on the clinical features of the primary AAV and their outcome.