Changing incidence and serotype trends in ANCA-associated vasculitis: a 30-year population-based study in Norfolk, UK

Abstract Objectives The ANCA associated vasculitides (AAV) are rare diseases with poor outcomes if untreated. Over a 30-year period we have investigated the changing incidence of AAV and its subtypes—Granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), eosinophilic GPA (EGPA), Proteinase 3 AAV (PR3 AAV), and Myeloperoxidase AAV (MPO AAV). Methods The study population included adults in the county of Norfolk, UK between 1991 and 2020. Diagnosis of AAV was made clinically and supported by EMA classification. Classification by ANCA subtype was possible from 2001. The overall incidence of clinical phenotypes GPA, MPA, EGPA, and serological phenotypes PR3 AAV and MPO AAV were analysed for temporal fluctuations and seasonality. Results From 1991–2020, the incidence (95% CI) of AAV, GPA, MPA, and EGPA was 25.1 (22.5, 27.9), 13.6 (11.7, 15.8), 8.5 (7.0, 10.2), and 3.0 (2.1, 4.0) per million person-years respectively. From 2001–2020, the incidence (95% CI) of PR3 AAV and MPO AAV was 11.5 (9.4, 13.9) and 11.7 (9.6, 14.1) per million person-years respectively. The temporal fluctuations in the incidence of EGPA and PR3 AAV were not significant. The incidence of GPA has a statistical periodicity of 9 years. The incidence of MPO AAV demonstrated a linear rise from 2001–2020 (R2=0.66). Our patients are getting older at diagnosis. Seasonality was not observed. Conclusion This is the longest incidence study of AAV in the world. The incidence of GPA showed a 9-year periodicity. The incidence of MPO AAV rose steadily. Its relationship to older age at diagnosis needs formal exploration.