ABS0309 INFLUENCE OF INITIAL AXIAL INVOLVEMENT ON THE PHENOTYPIC EVOLUTION OF AXIAL SPONDYLOARTHRITIS: 10-YEAR DATA FROM THE DESIR COHORT

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Background: Inflammatory back pain in axial spondyloarthritis (axSpA) can begin in a single segment of the spine or in multiple segments simultaneously. However, certain localizations may be more frequently associated with progression to specific rheumatological phenotypes or the development of particular extra-rheumatological manifestations. Objectives: To evaluate the influence of initial axial involvement in axSpA on subsequent clinical phenotype over a 10-year period. Methods: All patients with inflammatory back pain associated with recent axSpA included in the DESIR cohort, with data on the location of initial axial involvement, were included. The main endpoints were the occurrence of extra-axial manifestations (arthritis, dactylitis, enthesitis) and extra-rheumatological manifestations (psoriasis, uveitis, chronic inflammatory bowel diseases [IBD]). Patients were divided into three groups according to the initial location of their back pain (cervico-thoracic involvement, lumbosacral involvement, or diffuse involvement involving both segments) and were compared based on baseline demographic and clinical characteristics. The association between the initial location of back pain and the occurrence of extra-axial/extra-rheumatological manifestations was analyzed using a multivariate Cox model, adjusted for age, sex, exposure to csbDMARDs/bDMARDs (time-dependent variables), and the presence of these manifestations at baseline. Results: Among the 662 patients included, 94 (14.2%) had initial cervico-thoracic involvement (33.9±8.4 years; 53% men), 466 (70.3%) had lumbosacral involvement (33.0±8.6 years; 46% men), and 103 (15.5%) had diffuse involvement (36.0±8.6 years; 40% men). Patients with diffuse initial involvement were significantly older, had lower educational levels, and had a less frequent history of dactylitis at baseline compared to those with cervico-thoracic or lumbosacral involvement. After the onset of back pain, 222 (37.2%) patients experienced their first arthritis episode, 136 (21.6%) developed dactylitis, 382 (71.4%) developed enthesitis, 103 (18.1%) developed psoriasis, 91 (14.3%) developed uveitis, and 42 (6.6%) developed IBD. Figure 1 shows the survival curves based on initial spinal involvement. After adjustments, initial diffuse back pain was associated with a significantly higher risk of developing arthritis during follow-up (Hazard ratio=2.1; 95% confidence interval=1.3-3.4), compared to cervico-thoracic involvement. No other significant associations were found between the initial location of back pain and the subsequent axSpA phenotype. Other factors associated with each extra-axial or extra-rheumatological manifestation are detailed in Table 1. Conclusion: Only diffuse initial inflammatory back pain appears to be associated with later phenotypic evolution of axSpA, with a higher incidence of arthritis. This finding is relevant for clinicians, patient counseling, and the analysis of therapeutic trials. REFERENCES: NIL . Acknowledgements: NIL . Disclosure of Interests: Laura Pina Vegas: None declared , Maxime Dougados: None declared , Philippe Le Corvoisier: None declared , Salah Ferkal: None declared , Alain Luciani: None declared , Bastien Peiffer: None declared , PASCAL CLAUDEPIERRE Consultant for AbbVie, Amgen, Biogen, Celltrion, Galapagos, Janssen, Lilly, MSD, Novartis, Pfizer, and UCB (less than $10,000 each); investigator for AbbVie, Janssen, Lilly, MSD, Novartis, and Pfizer. © The Authors 2025. This abstract is an open access article published in Annals of Rheumatic Diseases under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Neither EULAR nor the publisher make any representation as to the accuracy of the content. The authors are solely responsible for the content in their abstract including accuracy of the facts, statements, results, conclusion, citing resources etc.

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