POS0944 AGE AT ONSET IN AXIAL SPONDYLOARTHRITIS AROUND THE WORLD: DATA FROM THE INTERNATIONAL ASAS-PERSPA STUDY
Authors: A. Boel, C. López-Medina, D. Van der Heijde, F. A. Van Gaalen
Journal: Annals of the Rheumatic Diseases (2021)

Background: Axial spondyloarthritis (axSpA) typically begins in young adulthood and age at onset is therefore very useful in identifying chronic back patients at an increased risk of axSpA. Age at onset below the age of 45 has been incorporated into the 2009 ASAS classification criteria for axSpA as a mandatory feature. However, inclusion of age at onset before the age of 45 was based on a small number of Western European studies and it is therefore unknown if this age at onset applies to patients in other parts of the world. Objectives: The aim of this study was to assess age at onset of axSpA as well as its relationship with HLA-B27 throughout the world, using data from the Assessment in SpondyloArthritis international Society (ASAS) peripheral involvement in Spondyloarthritis (ASAS-perSpA) study. Methods: Analyses were restricted to patients with an axSpA diagnosis who had information available on age at onset of axial complaints. Cumulative probability plots were used to graphically display the cumulative distribution of age at onset of axial symptoms. Linear regression models were built to assess the effect of HLA-B27 status on age at onset of axial symptoms. As axSpA is a multifactorial, multigenetic disease, geographical region was investigated as an effect modifier. Results: The majority (92%) of patients with axSpA had an age at onset of axial symptoms below 45 years, with only small variation across the various geographical regions (table 1). Cumulative distribution plots showed age at onset of axial symptoms was consistently lower in HLA-B27 positive patients (in blue) than in HLA-B27 negative patients (in red) across all geographical regions (Figure 1 below). Linear regression models showed a significant effect of HLA-B27 status on the age at onset of axial symptoms in the total study population (p&lt;0.001), and Latin American (p&lt;0.001), European &amp; North American (p&lt;0.001), Asian (p=0.006) and Middle Eastern &amp; North African (p=0.005) populations. There was no effect modification of geographical region (p=0.50) on the association between HLA-B27 status and age at onset of axial symptoms. Table 1. Percentage of axSpA patients with an age at onset of axial symptoms &lt;40, &lt;45 and &lt;50 years stratified by geographical region and HLA-B27 status. HLA-B27 positive HLA-B27 negative N Age at onset &lt;40 Age at onset &lt;45 Age at onset &lt;50 N Age at onset &lt;40 Age at onset &lt;45 Age at onset &lt;50 Asia 469 91% 94% 97% 56 79% 88% 95% Europe &amp; North America 678 88% 94% 98% 184 74% 85% 93% Latin America 157 81% 94% 96% 38 45% 76% 84% Middle East &amp; North Africa 320 88% 94% 98% 161 84% 88% 94% Total 1624 88% 94% 97% 439 76% 86% 93% Conclusion: Irrespective of geographical region, the majority of axSpA patients had an age at onset of axial disease before the age of 45. In all populations, HLA-B27 was associated with earlier disease onset. These results provide crucial data for diagnosis, classification, and policies aimed at improving recognition of axSpA. Figure 1. Acknowledgements: We would like to thank all ASAS-perSpA investigators and members of the scientific committee Disclosure of Interests: None declared