Classification of Antineutrophil Cytoplasmic Antibody-associated Vasculitis

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a group of systemic vasculitides, that are characterized by inflammation in the small vessels, ranging from capillaries to arterioles or venules. AAV is divided into three variants based on the clinical manifestations and histological findings such as microscopic polyangiitis (MPA), granulomatosis with polyangiitis (GPA) and eosinophilic GPA (EGPA). MPA often induces rapid progressive necrotising glomerulonephritis, and occasionally induces diffuse alveolar hemorrhage. In contrast, GPA preferentially affects the respiratory tracts from the bronchus to the nasal cavity. GPA can also involve the kidneys, but the frequency of renal involvement is less than MPA. EGPA is based on allergic components such as asthma, peripheral eosinophilia, migratory eosinophilic pneumonia and eosinophil infiltration. Since 1982, when the association between ANCA and systemic vasculitis was first reported, several classification criteria for AAV have been proposed. This review describes the classification criteria for and nomenclature of AAV from the 1990 American College of Rheumatology (ACR) classification criteria to the 2012 revised Chapel Hill consensus conference (CHCC) nomenclature of Vasculitides. New classification trials for AAV such as AAV based on the ANCA-types (myeloperoxidase-ANCA vasculitis, proteinase 3-ANCA vasculitis and ANCA negative vasculitis) and the ACR/European League Against Rheumatism (EULAR) 2017 provisional classification criteria for GPA were also introduced. In addition, the histopathological classification of ANCA-associated glomerulonephritis and the revised 2017 international consensus on testing of ANCAs in GPA and MPA are also discussed.