SAT0567 Prevalence Estimates of Axial Spondyloarthritis among Patients in German Rheumatology Practices
Authors: S. Rao, M. A. Cifaldi, A. D. Joshi, A. Shillington, M. McGuire, B. Wittig, M. Rudwaleit
Journal: Annals of the Rheumatic Diseases (2013)

<h3>Background</h3> The ASsessment in Ankylosing Spondylitis (ASAS) international Society working group has proposed and validated new classification criteria specific for axial SpA.<sup>1</sup> <h3>Objectives</h3> We applied these criteria to clinical data from a sample of German rheumatology practices to estimate the overall prevalence of nonradiographic axial SpA (nr-axSpA) and ankylosing spondylitis (AS) in Germany. <h3>Methods</h3> Patients experiencing chronic low back pain (at risk cohort) with age of onset between 18–44 years were identified among the patients in 41 German rheumatology practices. The at risk cohort was an estimate provided by the rheumatologists. Medical records were randomly selected from this at-risk cohort for review against ASAS axial SpA criteria. The proportion of patients meeting the ASAS criteria or using the diagnostic algorithm<sup>2</sup> was compared to an estimate of the total number of at risk patients treated at participating sites and was extrapolated to 1550 German rheumatology practices. Assuming 41 rheumatologists selected in this study are representative of the universe of rheumatologists in Germany, the prevalence estimate was calculated by dividing the estimate of patients with axial SpA by the total population aged ≥18 years.<sup>3</sup> <h3>Results</h3> In a sample of 206 randomly selected records of at-risk patients, rheumatologists diagnosed 179 (87%) patients with axial SpA of which 45.3% were considered to have nr-axSpA and 54.7% were considered to have AS. The diagnostic algorithm identified between 84–98 (40.7–47.5%) patients with nr-axSpA, based on the upper/lower range of probabilities and 53 (26%) patients with AS. The ASAS criteria was assessed against a population of 138 patients with radiographic imaging results (X-ray and MRI), 114 patients met the criteria for axial SpA of whom 61 (42.3%) had nr-axSpA and 53 (57.7%) patients with AS. By applying each of these ratios to the total pool of 209,250 at-risk patients, 174,375 patients were projected to meet ASAS criteria. This projection corresponds to a national prevalence estimate of 0.25% (ASAS; 95% CI: 0.23–0.27%). Similarly, our prevalence numbers of nr-axSpA estimated 0.13% (ASAS; 95% CI: 0.11–0.16%) and 0.12–0.14% (diagnostic algorithm; 95% CI: 0.10-0.14–0.12-0.16), showing a degree of overlap between the 2 methods in identifying nr-axSpA. The prevalence estimates for AS are 0.12% (95% CI: 0.09–0.15%). The ratio of axial SpA diagnosed by rheumatologists corresponds to a prevalence of 0.26% (95% CI: 0.25–0.28%). <h3>Conclusions</h3> This is the first retrospective epidemiology study of Axial SpA among rheumatologists in Germany. The prevalence of axial SpA based on the ASAS classification criteria was estimated to be approximately 0.25%, including 0.13% for nr-axSpA and 0.12% for AS. Sampling bias present from rheumatologist recruitment methodology and the projection of data to registered rheumatologists may have an indeterminate affect on the external validity of the results. Additionally, this study is only based on the patient population seen by rheumatologists and does not take into account patients that could be treated by orthopedics. <h3>References</h3> Rudwaleit M, et al. <i>Ann Rheum Dis.</i> 2009;68:770–83. Rudwaleit M, et al. <i>Ann Rheum Dis.</i> 2004;63:535–43. Statistisches Bundesamt, Wiesbaden 2009. <h3>Acknowledgements</h3> The authors would like to thank Eric Bertelsen and Cathryn M. Carter of Arbor Communications who provided medical writing and editing services in the development of this abstract. The financial support for these services was provided by AbbVie. <h3>Disclosure of Interest</h3> S. Rao Shareholder of: AbbVie, Employee of: AbbVie. The design, study conduct, and financial support for the study/trial was provided by AbbVie. AbbVie participated in the interpretation of data, review, and approval of the abstract., M. Cifaldi Shareholder of: AbbVie, Employee of: AbbVie. The design, study conduct, and financial support for the study/trial was provided by AbbVie. AbbVie participated in the interpretation of data, review, and approval of the abstract., A. Joshi Shareholder of: AbbVie, Employee of: AbbVie. The design, study conduct, and financial support for the study/trial was provided by AbbVie. AbbVie participated in the interpretation of data, review, and approval of the abstract., A. Shillington Employee of: EPI-Q, under contract w/AbbVie, M. McGuire Employee of: Medical Data Analytics, under contract w/AbbVie, B. Wittig Shareholder of: AbbVie, Employee of: AbbVie. The design, study conduct, and financial support for the study/trial was provided by AbbVie. AbbVie participated in the interpretation of data, review, and approval of the abstract., M. Rudwaleit Speakers bureau: AbbVie, BMS, MSD, Pfizer, Roche, UCB