Classification of ANCA-associated vasculitis: differences based on ANCA specificity and clinicopathologic phenotype

The classification of vasculitis according to a schema with universal acceptance is challenging, given the heterogeneous and protean nature of these diseases. Formal nomenclature and classification criteria for anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) have suffered several changes since their first description; none provides comprehensive diagnostic and classification criteria. Different factors account for the difficulties in the classification of vasculitis, including the incomplete understanding of the pathogenesis, the multisystemic nature of the disease, the non-specific patterns of vascular involvement, the overlap between entities, and the presence of various classification systems. The present article reviews the classification of AAV considering different points of view, including clinical, serologic, pathogenetic, organ predilection, therapeutic, and prognostic factors, and provides perspectives on future challenges in the understanding of AAV. There is an unmet need for a unifying view of the disease spectrum that considers the constantly evolving paradigms.