The risk of osteoporosis in patients with ankylosing spondylitis—A large retrospective matched cohort study

Background: Ankylosing spondylitis (AS) is associated with increased bone turnover and systemic inflammation. Osteoporosis is common but frequently underappreciated in AS, studies regarding the incidence of osteoporosis in AS are limited and based on small cohorts. The aim of this study is to assess the risk of osteoporosis in patients with AS compared to matched controls. Methods: A population based retrospective cohort study using data retrieved from a large electronic medical record in Israel, the Clalit health services. Included patients that were diagnosed with AS from January 2002 to December 2018 were followed for development of osteoporosis. The incidence of osteoporosis was compared between AS and controls and a logistic regression model was used to assess the interaction between AS and osteoporosis. Results: The study included 5476 AS patients, and 27,657 age- and sex-frequency matched controls. The incidence of osteoporosis in AS patients was significantly higher than controls (4.7% vs 2.8%, p < 0.001) in the whole cohort as well as when stratified by sex. Osteoporosis developed earlier in patients with AS versus controls (4.1 vs 5.2 years, p < 0.001). In multivariate analysis and after adjustment to several potential confounders, AS was found to independently associated with osteoporosis (HR 1.83, 95%CI 1.58–2.11, p < 0.0001). Conclusions: Our study confirms the higher incidence and earlier development of osteoporosis in patients with AS. Such finding highlights the increased need of awareness and earlier detection of such comorbidity allowing prompt treatment to prevent undesired sequalae including increased risk of fractures.