Primary renal vasculitis in Norfolk - increasing incidence or increasing recognition?

Background. The incidence of renal vasculitis has previously been estimated using histological definitions or only a single clinical diagnosis, e.g. W egener's Granulomatosis (WG). Our hospital is the single referral centre fo r the former Norwich Health Authority (NHA) which encompasses a stable, hom ogenous, well-defined and studied population. We estimated the overall inci dence of primary renal vasculitis and the incidence within individual clini cal disease classifications. Methods. All cases of primary renal vasculitis diagnosed within the NHA ove r 66 months (1992-1997) were identified by review of renal biopsies, the No rfolk Vasculitis Register, hospital discharge summaries and plasmapheresis records. Patients were classified using the 1990 American College of Rheuma tology criteria for Polyarteritis Nodosa (PAN), Churg Strauss Syndrome (CSS ) and Henoch-Schonlein Purpura; the Chapel Hill Consensus Conference Defini tions for Microscopic Polyangiitis (mPA) and the Lanham criteria for CSS. i ncidence figures were calculated using the NHA adult population of 413747 ( 1994). Ninety-five per cent confidence intervals (C.I.) were calculated usi ng the poisson distribution. Results. The overall annual incidence for primary renal vasculitis was 18/m illion (C.I. 12.9-24.4). The annual incidence of renal involvement of indiv idual diseases was as follows: WG 7.9/million (95% C.I. 4.7-12.5); mPA 7.5/ million (95% C.I. 4.4-12.0); PAN 7.0/million (95% C.I. 4.0-11.4); HSP 3.1/m illion (95% C.I. 1.2-6.3); CSS 1.3/million (95% C.I. 0.3-3.9). Conclusions. The annual incidence for primary renal vasculitis overall and the individual subtypes in Norfolk is much higher than previous European es timates. This may reflect an increasing incidence in primary renal vasculit is with time or underestimation in previous studies. However the incidence of renal vasculitis in our population is markedly lower than reported in Ku wait. There may therefore be true variation in incidence between population s which could have implications for the aetiology of primary vasculitis.