Systemic vasculitis is a rare but severe group of diseases characterized by inflammation and necrosis of blood vessels. The size of the vessel affected varies among the different forms of vasculitis and there are three main subgroups: large, medium and small vessel vasculitis. Among small vessel vasculitis, the antineutrophil cytoplasmic antibody (ANCA)-associated forms are of particular importance. This subgroup includes: microscopic polyangiitis, granulomatosis with polyangiitis (Wegener’s), eosinophilic granulomatosis with polyangiitis (Churg–Strauss) and the form limited to the kidney. ANCA are serum autoantibodies directed against proteins present in the cytoplasmic granules of neutrophils and represent the serological markers of small vessel vasculitis. Renal involvement is present in the majority of patients with ANCA-associated vasculitis (AAV) and the consequences of a missed or delayed diagnosis of renal vasculitis are potentially life threatening. Patient survival and the risk of end-stage renal disease are closely associated with renal function at presentation. The gold standard for diagnosis remains renal biopsy. In 2010, a new histopathological classification based on the percent of normal glomeruli, cellular crescent or global sclerotic glomeruli was proposed. The aim of this classification was to predict the renal prognosis. Nowadays, remission can be achieved and maintained in most cases with a combination of high-dose steroid and immunosuppressive drugs. This therapy has to be continued for at least 24 months after a substantial remission has been obtained because early cessation of treatment is associated with an increased risk of relapse. For this reason, patients should be regularly monitored in order to promptly diagnose and treat a possible recurrence of AAV. This review will focus on kidney involvement in AAV with an overview of the clinical–pathological characteristics and therapeutic strategy for these conditions.
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