[Renal manifestations in vasculitides of small and medium-sized vessels]

Small-vessel vasculitides, in particular, are frequently manifested in the kidneys. A distinction is made between antineutrophil cytoplasmic antibody (ANCA)-associated vasculitides (AAV) and immune complex vasculitides. Even within the AAVs there are differences with respect to renal involvement, which manifest as necrotizing glomerulonephritis (GN) but renal involvement is much rarer in eosinophilic granulomatosis with polyangiitis than in microscopic polyangiitis and granulomatosis with polyangiitis. Disease progression, organ manifestation and prognosis vary according to the ANCA status. In immune complex vasculitides (cryoglobulinemic vasculitis, IgA vasculitis, hypocomplementemic urticarial vasculitis and antiglomerular basement membrane, GBM, disease), endothelial-adjacent activation of neutrophilic granulocytes leads to local vessel wall damage with subsequent ischemic tissue damage, similar to AAV. The sparse evidence of immune complexes is different in pauci-immune AAV. Polyarteritis nodosa is a disease with variable clinical presentations with necrotizing vasculitis of small and medium-sized arteries. Intrarenal aneurysms and hemorrhages but not GN lead to renal damage. Diagnostically, the detection of specific autoantibodies (e.g. anti-GBM), cryoglobulins or increased complement turnover can be decisive. Renal biopsy with qualified immunohistopathology is particularly important in cases of initial manifestation and unclear constellation of findings. The treatment of renal vasculitis is adapted to the severity, stage of disease, extrarenal organ manifestation and pathogenesis. It ranges from glucocorticoid monotherapy to moderate immunosuppression, up to targeted biologic therapy, chemotherapy and plasmapheresis.