Epidemiological aspects of ankylosing spondylitis in Sweden. Characterization, prevalence and prognosis

Abstract: Ankylosing Spondylitis (AS) is a chronic, potentially disabling, inflammatory disease that poses a longstanding burden on the patient and the society. The epidemiology of AS in Sweden has not been extensively studied previously. Radiographic and self-perceived health information from 1,005 men aged 69-81 years, showed a prevalence of moderate to severe radiographic sacroiliitis of 1.4% (95% Confidence Interval (CI): 0.7-2.4), with modest impact on health. Medical records of a representative sample of 500 patients with a registered visit to a physician with a diagnosis of AS or undifferentiated spondyloarthritis (uSpA) in the National Patient Register (NPR) (2007-2009) were reviewed. These diagnoses had high validity, as 70% of patients with an AS diagnosis fulfilled the modified New York (mNY) criteria for AS and 79% of patients with a diagnosis of uSpA fulfilled any set of the SpA criteria. Based on clinically diagnosed patients with AS in the NPR, identification of referents from the general population and linkage of these two groups to other national registers, the prevalence and mortality of AS were studied. The prevalence of clinically diagnosed AS was 0.18% in 2009, with higher estimates in men, in northern Sweden, and in those with lower level of education. Men more often had anterior uveitis and treatment with TNF-inhibitors compared to women, and women had more often peripheral arthritis, psoriasis and treatment with oral glucocorticosteroids. The all-cause mortality was increased in patients with AS compared to the general population, overall (age- and sex-adjusted hazard ratio (HR) 1.60 (95% CI: 1.44-1.77)) and separately for males and females. Predictors of death within the AS cohort included a lower level of formal education, general co-morbidities and joint surgery.