Histopathologic classification of anti-neutrophil cytoplasmic antibody-associated glomerulonephritis: achievements, limitations, and perspectives

Clinical and histological factors have been identified as predictors of early and late renal outcome in ANCA-associated vasculitides (AAV). The presence and severity of kidney involvement at diagnosis are associated with poor prognosis in both patient and renal survival. Histologic findings remain the gold standard for diagnosing patients with AAV. In order to quantify the extent of the morphological parameters in the renal biopsies and to identify the histopathological lesions that predict renal outcome, several scoring systems have been proposed to systematically assess kidney biopsies in AAV. Renal pathologists from an international working group proposed in 2010 a new histopathological classification. This scheme comprises four general categories, based on the predominance of the glomerular histological lesions: focal (≥50% normal glomeruli); crescentic (≥50% glomeruli with cellular crescents); mixed (<50% normal, <50% crescentic, <50% globally sclerotic glomeruli), and sclerotic (≥50% globally sclerotic glomeruli). This article reviews the background and the main studies that have validated the histopathologic classification of ANCA-associated glomerulonephritis, the conclusions derived from these studies, and the perspectives for the assessment of renal outcome in AAV.