Epidemiology of biopsy proven giant cell arteritis in northwestern Spain: trend over an 18 year period.

OBJECTIVE In Europe giant cell arteritis (GCA) is more common in Scandinavian countries than in southern regions. Epidemiological studies on GCA in other more distant countries have indicated a progressive increase in incidence. A regular cyclical pattern in incidence of GCA over 20 years has been reported in Olmsted County (Minnesota, USA). In contrast, no cyclical fluctuation has been recently reported in Sweden. To investigate further the epidemiology of GCA in southern Europe the trend in incidence and fluctuations of this vasculitis over 18 years in the Lugo region of northwestern Spain were examined. METHODS A retrospective study of biopsy proven GCA diagnosed between 1 January 1981 and 31 December 1998 at a single hospital for a well defined population of almost 250 000 people. Annual incidence was calculated for the whole group of patients and for men and women separately. Monthly variations, annual peaks of incidence, and trend in the incidence of biopsy proven GCA with and without polymyalgia rheumatica (PMR) were also examined. RESULTS One hundred and sixty one Lugo residents were diagnosed with biopsy proven GCA between 1981 and 1998. The average annual incidence for the population aged 50 and older was 10.24/100 000 (men 11.00/100 000, women 9.57/100 000). A progressive increase in the incidence in both men and women was seen. In men there was an annual increase of 8% (95% CI 4% to 13%; p<0.0001). In women the annual increase was 11% (95% CI 5% to 17%; p<0.0001). The overall annual increase for men and women was 10% (95% CI 6% to 14%; p<0.0001). No seasonal pattern or peaks in the incidence were seen. During the period 1981-94 GCA was more common in men than in women. In contrast, during the last years of study the increase in incidence was higher in women. In women the annual ratio of incidence of GCA with PMR/incidence of GCA without PMR was generally higher than 1. However, in men the annual ratio was initially 1 but decreased gradually, indicating a progressive decrease in the proportion of men with biopsy proven GCA associated with PMR. CONCLUSION In northwestern Spain there has been a progressive increase in GCA incidence. As seen in other countries where GCA is more common, during the past few years the increase in incidence has been mainly due to a higher number of new cases in women.