Investigations in systemic vasculitis - The role of renal pathology.

ANCA-associated vasculitis (AAV) describes a group of small-vessel vasculitides with frequent renal involvement. The first description of these conditions can be traced back to the 19th-century paper on necrotizing vasculitis by Kussmaul and Maier. Since then, our understanding of the pathogenesis has improved and the histopathological lesions have been described in detail. Characteristic histologic lesions in ANCA-associated glomerulonephritis (AAGN) are fibrinoid necrosis and crescents, often accompanied by tubulointerstitial inflammation. The discovery of ANCAs has not rendered renal biopsies obsolete in the diagnostic process. Currently, renal biopsies remain the gold standard for the diagnosis of AAV in conjunction with ANCA serology. In addition to diagnosis, renal biopsies are useful for patient prognosis. The evaluation of renal histological samples from patients with new-onset AAV who participated in clinical trials led to the proposal of the histopathological classification for AAGN. The prognostic value of this classification continues to be validated and an update is expected soon.