The incidence of giant cell arteritis in Ontario, Canada

Objective The incidence of giant cell arteritis (GCA) is insufficiently documented for Canada, but important to ascertain for public health planning. We estimate the incidence of biopsy-proven GCA (BPGCA) in Kingston, Ontario, and for the province of Ontario. Method The number of cases of BPGCA was tabulated from retrospective chart review of all temporal artery biopsies (TABx) in Kingston, Ontario from 2011–15. The relevant population denominator was determined from the Canada census federal electoral district and the patient’s postal code. The province-wide estimate for the incidence of BPGCA was calculated from provincial billing data of TABx from 2015–17, the Canada census for Ontario, and the expected positive yield of TABx. Results There were 35 subjects with BPGCA in the Kingston area over the 4-year period, from a population of 179 503 individuals 50 years of age or older (≥50 years). Ontario billing data identified 2404 patients who underwent TABx for suspected GCA over a 2-year period, from a population of 5 143 610 persons ≥50 years. Meta-analysis of 5 provincial TABx series suggested a 21% positive yield from TABx procedures (95% CI 0.18–0.24). The minimum cumulative incidence of BPGCA was 4.9 per 100 000 persons ≥50 years in Kingston, and 4.9 (95% CI 4.2–5.6) per 100 000 persons ≥50 years for Ontario as a whole. Conclusion The estimated incidence of BPGCA in Ontario using 2 different estimation techniques was comparable, but low compared with other countries. The actual incidence of GCA in Ontario may be higher.