Objective: The aim of this work was to study changes in the incidence of biopsy-proven giant cell arteritis (GCA) over a period of 20 yr in Göteborg, Sweden.
Methods: All cases of biopsy-verified GCA between 1976 and 1995 were included in the study. The annual incidence was calculated for the whole material, for women and men separately, and its fluctuations were tested statistically. In addition, the monthly variation during the last 9 yr could be statistically analysed for the whole material.
Results: In total, 665 patients were diagnosed with biopsy-verified GCA during the 20 yr period. The average annual incidence was 22.2/100000 inhabitants over 50 yr of age (women 29.8, men 12.5). The annual incidence increased significantly with time (P<0.001) for both men and women. Statistical analysis did not reveal any cyclic fluctuation in the annual incidence (P=0.26), while the monthly number of positive biopsies showed significant fluctuation with peaks in late winter and autumn (P=0.041).
Conclusions: The annual incidence of biopsy-positive GCA increased during the years 1976 through 1995. The significant seasonal variation, as well as considerable variation in annual incidence, might be due to the influence of exogenous triggering factors, such as infections. Further support for an exogenous aetiology, in terms of a statistically significant cyclic fluctuation of the annual incidence, was not found, however.