The epidemiology of biopsy-positive giant cell arteritis: special reference to cyclic fluctuations

Objective. The aim of this work was to study changes in the incidence of bi opsy-proven giant cell arteritis (GCA) over a period of 20 yr in Goteborg, Sweden. Methods. All cases of biopsy-verified GCA between 1976 and 1995 were includ ed in the study. The annual incidence was calculated for the whole material , for women and men separately, and its fluctuations were tested statistica lly. In addition, the monthly variation during the last 9 yr could be stati stically analysed For the whole material. Results. Tn total, 665 patients were diagnosed with biopsy-verified GCA dur ing the 20 yr period. The average annual incidence was 22.2/100 000 inhabit ants over 50 yr of age (women 29.8, men 12.5). The annual incidence increas ed 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 fl uctuation with peaks in late winter and autumn (P = 0.041). Conclusions. The annual incidence of biopsy-positive GCA increased during t he years 1976 through 1995. The significant seasonal variation, as well as considerable variation in annual incidence, might be due to the influence o f exogenous triggering factors, such as infections. Further support for an exogenous aetiology, in terms of a statistically significant cyclic fluctua tion of the annual incidence, was not found, however.