During most of the 20th century, the medical literature on systemic vasculitis has been dominated by “splitters,” who sought to characterize the precise clinical and pathologic differences among these diseases. However, in the past decade in particular, those interested in renal vasculitis have tended to become “lumpers,” who stressed overlap, particularly among patients with microscopic polyarteritis, necrotizing and crescentic glomerulonephritis, and Wegener's granulomatosis. The discovery of antineutrophil cytoplasmic antibodies has provided additional evidence of commonality among these renal vasculitides. The overlapping extended, to a considerable extent, to therapy as well. In the presence of severe glomerulonephritis, there is general consensus that methylprednisolone and cyclophosphamide are the preferred induction therapies. Controlled trials mostly fail to support the efficacy of adjunctive plasma exchange. Attempts to minimize risks of cyclophosphamide therapy focus on maintenance therapy with azathioprine or intermittent pulse cyclophosphamide. Contemporary series show that 5-year patient and kidney survival rates with antineutrophil cytoplasmic antibody-associated renal vasculitis range from 60% to 80%.
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