Microscopic polyangiitis (mpa)

[Ernesto]

Microscopic polyangiitis is a systemic necrotizing vasculitis without immune globulin deposition (pauci-immune) that affects mainly small vessels. It may begin as a pulmonary-renal syndrome with rapidly progressing glomerulonephritis and alveolar hemorrhage, but the pattern of disease depends on the organs affected. Diagnosis is made by clinical findings and sometimes confirmed by biopsy. Treatment, which depends on disease severity, includes corticosteroids and immunosuppressants.
(See also Overview of Vasculitis.)
Microscopic polyangiitis (MPA) is rare (about 13 to 19 cases/million). Pathogenesis is unknown. MPA affects small vessels and is pauci-immune (ie, immune globulin deposition is not seen on tissue biopsy), similar to granulomatosis with polyangiitis (GPA) and eosinophilic granulomatosis with polyangiitis (EGPA), which differentiates it from immune complex-mediated small-vessel vasculitides (eg, immunoglobulin A–associated vasculitis—formerly known as Henoch-Sch#246;nlein purpura) and small-vessel cutaneous vasculitis. MPA affects predominantly small vessels (including capillaries and postcapillary venules), unlike polyarteritis nodosa, which affects medium-sized muscular arteries. Older literature (ie, before 1994) did not adequately distinguish between polyarteritis nodosa and MPA―alveolar hemorrhage and glomerulonephritis can occur in MPA but not in polyarteritis nodosa. Rarely, MPA can occur in association with hepatitis B.
Clinical manifestations resemble those of granulomatosis with polyangiitis except that granulomatous destructive lesions (eg, pulmonary cavitary lesions) are absent and the upper respiratory tract is usually affected minimally or not at all. In both disorders, antineutrophil cytoplasmic antibodies (ANCA) may be present.