Antineutrophil cytoplasmic antibodies (ANCA) and abnormal angiograms in polyarteritis nodosa and Churg-Strauss syndrome: indications for the diagnosis of microscopic polyangiitis.

Microscopic polyangiitis (MPA) is one of the vasculitides previously included in the polyarteritis nodosa (PAN) group. A diagnosis of MPA is usually considered when glomerulonephritis and/or lung hemorrhage are present. Small-sized vessels are involved and this sign is considered, for some authors, to be the main diagnostic criterion. The present study attempted to define clinical, radiological and immunological characteristics of MPA and to separate them from classic PAN (c-PAN) and Churg-Strauss syndrome. We have shown that, in most cases, patients presenting microaneurysms and/or multiple vessel stenoses, which reflect medium-sized vessel involvement, do not have ANCA. Conversely, patients with glomerulonephritis have almost never had abnormal angiograms. Furthermore, the clinical characteristics of ANCA-positive patients also indicate small-sized vessel involvement. Although at present it is not possible to definitively separate MPA from c-PAN, our results show that ANCA should be considered diagnostic for MPA and, in most cases, should be an exclusion criterion for c-PAN.