Microscopic polyangiitis.

Abstract

Microscopic polyangiitis is a systemic vasculitis affecting smal-l and medium-sized vessels and is characteristically associated with a focal and segmental necrotizing glomerulonephritis. It may present as a pulmonary-renal syndrome with rapidly progressive glomerulonephritis and alveolar hemorrhage, but the pattern of disease will vary according to the organ systems involved. Granulomatous disease of the upper or lower respiratory tract is not a feature, and its presence suggests the diagnosis of Wegener's granulomatosis. The etiology of the condition is unclear, but most patients have antineutrophil cytoplasm antibodies (ANCA) with specificity for either myeloperoxidase (MPO) or proteinase 3 (PR3), and there is increasing evidence that these may be pathogenic. Current treatment includes an induction phase using cyclophosphamide and steroids to attain remission, followed by a maintenance phase in which the levels of immunosuppression are gradually reduced. Azathioprine may be substituted for cyclophosphamide at 3 months. Adjunctive plasma exchange or intravenous methylprednisolone is used in the management of either or both severe renal disease and alveolar hemorrhage, and new evidence suggests that plasma exchange is more effective in recovery of renal function. Overall, 1-year survival in systemic vasculitis is around 85%, and up to 50% of patients relapse, although relapse is less common in those with MPO-ANCA. Newer therapies are being explored in an attempt to increase the efficacy and reduce the toxicity of treatment.