Pathology of ANCA-associated vasculitis.

According to the recent 2012 Chapel Hill Consensus Conference, ANCA-associated vasculitis is classified in the group of small vessel vasculitis. Pauci-immune necrotizing crescentic glomerulonephritis is the morphological hallmark of ANCA-associated vasculitis. Crescentic damage of the glomerular tuft is characterized by macrophage accumulation through vascular cell adhesion molecule-1 (VCAM-1) activation. Macrophages have a key role in chronic progression of renal damage due to production of substances involved in matrix remodelling [transforming growth factor-beta (TGFβ)]. Diffuse interstitial infiltration of T and B lymphocytes and macrophages is another frequent morphological feature. Tubulitis is considered an important marker of worse prognosis. Unfortunately, the renal changes on long-term follow-up are largely unknown due to the small number of studies with repeat biopsy in these disorders. Although a standardized score for renal biopsies was developed previously, a final histopathologic classification is still lacking. The European Vasculitis Study Group (EUVAS) proposed a classification system based on glomerular pathology as assessed by light microscopy.