Incidence of giant cell arteritis in Western Norway 1972-2012: a retrospective cohort study

Background: Giant cell arteritis (GCA) is the most common systemic vasculitis in persons older than 50 years. The highest incidence rates of the disease have been reported in Scandinavian countries. Our objective was to determine the epidemiology of GCA in an expected high-incidence region during a 41-year period. Methods: This is a hospital-based, retrospective, cohort study. Patients diagnosed with GCA in Bergen health area during 1972-2012 were identified through computerized hospital records (n = 1341). Clinical information was extracted from patients' medical journals, which were reviewed by a standardized method. We excluded patients if data were unavailable (n = 253), if the reviewing rheumatologist found GCA to be an implausible diagnosis (n = 207) or if the American College of Rheumatology (ACR) 1990 classification criteria for GCA were not fulfilled (n = 89). Descriptive methods were used to characterize the sample. Incidence was analyzed by graphical methods and Poisson regression. Results: A total of 792 patients were included. The average annual cumulative incidence of GCA was 16.7 (95% CI 15. 5-18.0) per 100,000 of the population = 50 years old. The corresponding incidence for biopsy-verified GCA was 11.2 (95% CI 10.2-12.3). The annual cumulative incidence increased with time in the period 1972-1992 (relative risk (RR) 1.1, p< 0.001) but not in 1993-2012 (RR 1.0, p = 0.543). The incidence was higher in women compared to men (average annual incidence 37.7 (95% CI 35.8-39.6) vs. 14.3 (95% CI 13.2-15.5), p < 0.001) with women having a twofold to threefold higher incidence rate throughout the study period. Average annual incidence increased with age until the 7th decade of life in both sexes throughout the study period (2.8 (95% CI 2.3-3.3) for age < 60, 15.5 (95% CI 14.4-16.8) for age 60-69, 34.5 (95% CI 32.8-36.4) for age 70-79 and 26.8 (95% CI 25.3-28.4) for age = 80 years, p < 0.001 for all age adjustments). Conclusions: Our study confirms an incidence of GCA comparable to previous reports on Scandinavian populations. Our results show increasing incidence from 1972 through 1992, after which the incidence has levelled out.