Relationship between ANCA and disease activity in small vessel vasculitis patients with anti-MPO ANCA

Background. We analysed the usefulness of antineutrophil cytoplasmic antibo dies (ANCA) as a marker of clinical activity in patients with small vessel vasculitis associated with anti-myeloperoxidase (MPO) ANCA. Methods. We studied a group of 25 patients, 15 with microscopic polyangitis and 10 with renal limited vasculitis, so-called rapidly progressive glomer ulonephritis type III. The clinical and serological follow-up was accomplis hed quarterly over an average of 2.79 +/- 2.08 years (range 0.25-6 years). ANCA was analysed by indirect immunofluorescence and enzyme-linked immunoso rbent assays (ELISAs). Results. At the time of diagnosis, all patients were ANCA positive (P-ANCA and anti-MPO). Following a standardized treatment, all patients except one achieved complete remission of vasculitis in <3 months. One patient suddenl y died during the active phase (1 month of follow-up) and with positive ANC A. Seroconversion from positive to negative occurred in 24/25 patients (96% ). Eighteen of these 24 patients (75%) achieved the seroconversion within t he first 6 months. During the follow-up, two patients had four major relaps es, all of them associated with positive ANCA. ANCA seroconversion from neg ative to positive was observed in one patient with microscopic polyangitis without clinical relapse of vasculitis. Conclusion. ANCA should be used in conjunction with other markers of diseas e activity in the management of microscopic polyangitis and renal limited v asculitis patients with anti-MPO ANCA.