Incidence of ANCA-associated primary renal vasculitis in the Miyazaki Prefecture: the first population-based, retrospective, epidemiologic survey in Japan.

Clinicoepidemiological manifestations of the vasculitides differ geographically. According to a nationwide, hospital-based survey in Japan, the prevalence of microscopic polyangiitis (MPA) and/or renal-limited vasculitis (RLV) is much higher than that of Wegener's granulomatosis (WG). However, little is known about the incidence of antineutrophil cytoplasmic autoantibodies (ANCA)-associated primary renal vasculitis (PRV) in Japan. The incidence of PRV was retrospectively determined by a population-based method in Miyazaki Prefecture in Japan between 2000 and 2004. PRV was defined according to the following criteria from the European Systemic Vasculitis Study Group: (1) new patients with WG, MPA, Churg-Strauss syndrome (CSS), or RLV, (2) renal involvement attributable to active vasculitis, and (3) ANCA considered positive if the disease was not histologically confirmed. The numbers of patients with PRV in the years 2000, 2001, 2002, 2003, and 2004 were 9, 9, 9, 16, and 13, respectively. The male to female ratio was 24:32 and the average age was 70.4 +/- 10.9 (mean +/- SD) yr. The estimated annual incidence of PRV was 14.8 (95% confidence interval [CI] 10.8 to 18.9) and 44.8 (95% CI 33.2 to 56.3) per million adults (>15 yr old) and seniors (>65 yr old), respectively. Ninety-one percent of the patients were myeloperoxidase (MPO)-ANCA positive, but none were positive for proteinase 3 (PR3)-ANCA. There were no WG or CSS patients. The incidence of PRV did not differ between Japan and Europe, but WG was not widespread in Japan. Furthermore, the ratio of serum MPO to PR3-ANCA among Japanese with PRV was much higher than that found among European and US patients.