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

Objective: To report the annual and age-specific incidence of ANCA associated vasculitis and polyarteritis nodosa in the adult population of Norfolk County, UK.

Methods: Individuals newly diagnosed with ANCA associated vasculitis or polyarteritis nodosa between 1st Jan 2011 and 31st 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: 164 patients were diagnosed with ANCA associated vasculitis or polyarteritis nodosa over 4.7-million-person years. The annual incidence (95% CI) of ANCA associated vasculitis was 34.3 (29.2, 40)/million person years. The annual incidence for 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 for polyarteritis nodosa 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).

Conclusions: The incidence of ANCA associated vasculitis, specifically that of granulomatosis with polyangiitis and microscopic polyangiitis is slowly rising over time. It is most notable amongst the elderly population where 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.