Ankylosing spondylitis in Northern Norway

Ankylosing spondylitis (AS) is a relatively common inflammatory rheumatic disease (ref Gran, Kaipiainen-Seppenen) and the relationship to HLA B27 has been firmly established (Brewerton, Lancet 1973). Prevalence in different populations has been found to differ considerably. Whereas a prevalence of 6 % has been found among some native populations on the North-American subcontinent (Gofton, Ann Rheum Dis, 1966), AS is virtually non-existent in certain African populations (ref). This has been linked to the prevalence of HLA B27, but a recent study from Brown et al, showed no cases of AS in a Gambian population, in spite of a reported prevalence of HLA B27 of 6%.
Reports on the incidence of AS are, however, scarce. Based on hospital records, Carbone et al. found the incidence of AS in Rochester, Minnesota, USA, to be 7.3/100,000(ref.). In a Finnish study Kaipiainen-Seppenen et al. estimated the prevalence of clinically significant AS to be 0.15%, and reported an incidence of 6.9 per 100,000. The Finnish survey also found a considerably higher age of onset than Carbone et al., which may be due to study design.
The region of Northern Norway has a higher prevalence of HLA B27 and AS than the southern part of the country, probably due to the higher proportion of Samis in this region.

The department of Rheumatology at the University Hospital of Northern Norway, Tromsø, was founded in 1977. It is the only department of rheumatology in the two northernmost counties in Norway, Troms and Finnmark, serving a population of 225,000. There are three additional hospitals in this region, all of them referring rheumatic patients to our department, and we are, of course, the referring hospital for the general practitioners in both counties. We therefore have a unique possibility to conduct epidemiological surveys concerning rheumatic diseases in this region, and the main aim of this study was to calculate the minimum incidence of AS in the counties of Troms and Finnmark.