Incidence of ANCA-associated vasculitis and polyarteritis nodosa in Norfolk, UK, from 2011 to 2020

Objective The aim of this study was to report the annual and age-specific incidence of AAV and PAN in the adult population of Norfolk County, UK.Methods Individuals newly diagnosed with AAV or PAN between 1 January 2011 and 31 December 2020 residing in the postal areas of NR1-NR30 were included. Patients were classified according to the European Medicines Agency algorithm. Population data were available from the Office of National Statistics, UK.Results A total of 164 patients were diagnosed with AAV or PAN over 4.7 million person-years. The annual incidence (95% CI) of AAV was 34.3 (29.2, 40)/million person-years. The annual incidence (95% CI) of granulomatosis with polyangiitis, microscopic polyangiitis, and eosinophilic granulomatosis with polyangiitis was 18.9 (15.2, 23.3), 12.8 (9.7, 16.4) and 2.6 (1.3, 4.5)/million person-years, respectively. The annual incidence (95% CI) for PAN was 0.6 (0.1, 1.9)/million person-years. The age-specific incidence of granulomatosis with polyangiitis and microscopic polyangiitis rose with each decade of life and was highest in the 8th decade for granulomatosis with polyangiitis [53.2 (95% CI 36.2, 75.6) per million] and in the 9th decade for microscopic polyangiitis [48.4 (95% CI 27.1, 79.8) per million].Conclusion The incidence of AAV, specifically that of granulomatosis with polyangiitis and of microscopic polyangiitis, is slowly rising over time. It is most notable among the elderly population, among whom the incidence rates for granulomatosis with polyangiitis and microscopic polyangiitis peak. There may be a 4-year incidence cycle, which needs confirmation in a longer study.