Page 202 - The Vasculitides, Volume 1: General Considerations and Systemic Vasculitis

178 Constantina Yiannakis, Lorna Ward and Matthew David Morgan

Introduction

The anti-neutrophil cytoplasm antibody (ANCA)-associated vasculitides (AAV) include
are a group of rare life-threatening, autoimmune disorders that include microscopic
polyangiitis (MPA) and its renal limited variant (RLV); granulomatosis with polyangiitis
(GPA), previously known as Wegener granulomatosis (WG), and eosinophilic granulomatosis
with polyangiitis (EGPA), formerly Churg-Strauss syndrome. Although each disease has
distinctive features, there is considerable overlap in their clinical expression. This article
reviews the current understanding of classification and pathogenesis of AAV with an
emphasis on MPA, RLV, and GPA.

Epidemiology

The AAV occur with an annual incidence of <10 per million population [1, 2] and a peak
age of onset in the seventh to eighth decade of life [3]. They form a highly heterogeneous
group, both in terms of severity and organ involvement, and clinical manifestations.

Nomenclature and Classification

Although there are no diagnostic criteria, the Chapel Hill Consensus Conference (CHCC)
(Table 1) [4a] provided useful nomenclature and definitions for the classification of the
vasculitides, classifying AAV as small-vessel vasculitides (SVV) according to the caliber of
the vessels involved and the associated clinicopathological features. Table 2 shows an extent
and severity categorization of AAV utilized by the European Vasculitis Study Group
(EUVAS) [5]. The 2012 Revised CHCC classification and validated diagnostic criteria was
recently published [4b].

Table 1. Chapel Hill Consensus Conference on the Nomenclature of
Systemic Vasculitis: Definitions*

Granulomatosis with polyangiitis Granulomatous inflammation involving the respiratory
(GPA) tract, and necrotizing vasculitis affecting small to
medium-sized vessels (e.g. capillaries, venules, arterioles,
Microscopic polyangiitis (MPA) and arteries). Necrotising glomerulonephritis is common.
Necrotising vasculitis, with few or no immune deposits,
Renal limited vasculitis (RLV) affecting small vessels (i.e. capillaries, venules, or
*Adapted from reference [4a]. arterioles). Necrotizing arteritis involving small and
medium-sized arteries may be present. Necrotising
glomerulonephritis is very common. Pulmonary
capillaritis often occurs.
Pauci-immune necrotizing glomerulonephritis with no
apparent extra-renal features at presentations.

Complimentary Contributor Copy