SAT0534 Annual incidence of giant cell arteritis in urban and rural areas in western norway 1972–2012
Authors: L.K. Brekke, B.-T. S. Fevang, G. Myklebust
Journal: Annals of the Rheumatic Diseases (2018)

<h3>Background</h3> Giant cell arteritis (GCA) is the most common vasculitis in adults. The etiology is not fully understood, and environmental factors which may influence the incidence are poorly investigated. <h3>Objectives</h3> To determine the potential influence of rural or urban residence on the incidence of GCA during a 41 year period. <h3>Methods</h3> Hospital-based retrospective cohort study including patients diagnosed with GCA in Bergen Health Area during 1972–2012. Patients were identified through computerised hospital records using the International Classification of Diseases (ICD)-coding system. Clinical information was extracted by review of the patients' medical journals. The patients' residential address was obtained from the population register in Norway. Municipalities were classified as urban (code 1 and 2) or rural (code 3 thru 6) using the <sup>Statistics Norway 2017</sup> classification of centrality. The background population data was obtained from Statistics Norway (www.ssb.no). Wilcoxon signed-rank test was used for statistical comparison. <h3>Results</h3> The inclusion process have been published previously.<sup>1</sup> For the computing of incidence 743 patients were included. Among these there were 536 (72%) females (mean age 73.4 years, SD 8) and 207 (28%) males (mean age 72.6, SD 9). 493 patients (66%) had a positive temporal artery biopsy. 484 patients (65%) had a residential address in a municipality classified as urban and 259 (35%) in a rural municipality. The number of inhabitants (aged ≥50 years) in urban areas (i.e. city of Bergen) was 60 910 in 1972 and 81 972 in 2012. The corresponding number of inhabitants in rural areas was 30 320 and 51 401. The overall annual cumulative incidence of GCA was 16.7 (95% CI 15.5–18.0) per 100 000 persons≥50 years. The mean annual incidence for urban municipalities was 17.1 (95% CI 15.9–18.4) per 100 000≥50 years. The corresponding incidence for rural areas was 16.1 (95% CI 14.9–17.3), p=0.46. With regards to biopsy-proven GCA, the overall annual incidence was 11.2 (95% CI 10.2–12.3). In urban and rural areas, the incidence of biopsy-proven GCA was 11.7 (95% CI 10.6–12.7) and 10.4 (95% CI 9.4–11.4) respectively, p=0.10. There were large fluctuations in annual incidence in both urban and rural areas (figure 1). <h3>Conclusions</h3> Annual cumulative incidence of GCA was slightly higher in urban than in rural areas in our study, but the difference was not statistically significant. This is in contrast to a previous study, which found GCA more prevalent in urban than in rural populations.<sup>2</sup> Further studies are required to determine whether there is a true difference in incidence of GCA in urban versus rural populations, and whether or not exposures to environmental factors may be involved in GCA pathogenesis. <h3>References</h3> [1] Brekke LK, et al. Incidence of giant cell arteritis in Western Norway 1972–2012: a retrospective cohort study. Arthritis Research &amp; Therapy (2017) 19:278. doi:10.1186/s13075–017–1479–6 [2] Reinhold-Keller E, et al. Giant cell arteritis is more prevalent in urban than in rural populations: results of an epidemiological study of primary systemic vasculitides in Germany. Rheumatology (Oxford)2000;39(12):1396–402. <h3>Disclosure of Interest</h3> L. Brekke Grant/research support from: MSD, B.-T. Fevang Consultant for: Lilly, Novartis, AbbVie, G. Myklebust: None declared