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BackgroundPatients (pts) with axial spondyloarthritis (axSpA) are classified into radiographic axSpA (r-axSpA) and non-radiographic axSpA (nr-axSpA) based on the presence or absence of radiographic sacroiliitis. Approximately 20% to 80% of newly diagnosed axSpA pts have nr-axSpA and 8% to 40% progress to r-axSpA over the next 2 to 10 years.ObjectivesTo evaluate progression from nr-axSpA to r-axSpA over 5 years in a prospective multicentre cohort.MethodsPROOF was a global, real-world, prospective, observational study conducted in rheumatology clinical practices in 29 countries across 6 different geographic regions.1 The study enrolled adults with chronic back pain for ≥3 months and onset before 45 years of age. This analysis included pts diagnosed with axSpA who also fulfilled the Assessment of SpondyloArthritis international Society (ASAS) classification criteria for axSpA. Study visits occurred at baseline (BL) and yearly thereafter. Baseline and follow-up radiographs of sacroiliac joints (SIJ) were evaluated for pts with initial nr-axSpA diagnosis independently by 2 central readers according to the modified New York criteria. In the case of disagreement on the classification (nr- or r-axSpA), images were adjudicated by a third reader. Radiographic progression from nr-axSpA to r-axSpA over 5 years was evaluated by Kaplan-Meier analysis. Cox proportional hazards regression analyses for time to radiographic progression from nr-axSpA to r-axSpA were conducted. For model 1, ‘imaging arm vs clinical arm’ was used as an independent variable, and for model 2, ‘active inflammation on magnetic resonance imaging highly suggestive of sacroiliitis associated with SpA’ was used. Further, potential predictive factors included in the models were age, gender, back pain duration, number of SpA parameters, smoking status, CRP, good response to NSAIDs, HLA-B27 status, and current use of NSAIDs and TNF inhibitors.ResultsAmong 2633 enrolled pts, 2165 (82%) were diagnosed with axSpA and fulfilled the ASAS classification criteria. Among these, 1612 (74%) were classified as having r-axSpA (1050 [65%]) or nr-axSpA (562 [35%]) by central reading. The majority of nr-axSpA pts (77%) fulfilled the ASAS classification criteria due to positive findings on imaging (plus ≥1 SpA feature) and 23% were classified according to the clinical arm. A total of 246 nr-axSpA pts who had ≥1 follow-up SIJ radiograph were included in this analysis. Among these 246 pts, progression from initial nr-axSpA to r-axSpA at any of the follow-up visits was observed in 40 pts (16%) over 5 years. Mean time to radiographic progression was 2.4 years (ranging from 0.9 to 5.1 years) in descriptive analysis (Kaplan-Meier curve shown in Figure 1). In model 1 of the Cox regression analysis, male gender (hazard ratio [HR]: 3.16 [95% CI: 1.22–8.17]; P=0.0174), fulfilment of the imaging arm (HR: 6.64 [1.37–32.25]; P=0.0188), and good response to NSAIDs, (HR: 4.66 [1.23–17.71]; P=0.0237), were significantly associated with progression to r-axSpA (Figure 1). In model 2, HLA-B27 positivity showed a significant association with progression (HR: 3.99 [1.10–14.49]; P=0.0353; Figure 1).ConclusionIn this study, 16% of nr-axSpA pts progressed to r-axSpA within 5 years. The mean time to disease progression was 2.4 years. Predictors of radiographic progression were male gender, good response to NSAIDs, and fulfilment of the imaging arm as well as HLA-B27 positivity.References[1]Poddubnyy D. et al, Rheumatology (Oxford). 2021; doi: 10.1093/rheumatology/keab901Disclosure of InterestsDenis Poddubnyy Speakers bureau: AbbVie, Bristol Myers Squibb, Eli Lilly, MSD, Novartis, Pfizer, and UCB, Consultant of: AbbVie, Biocad, Eli Lilly, Gilead, GlaxoSmithKline, MSD, Novartis, Pfizer, Samsung Bioepis, and UCB, Grant/research support from: AbbVie, Eli Lilly, MSD, Novartis, and Pfizer, Joachim Sieper Speakers bureau: AbbVie, Janssen, Merck, Novartis, Pfizer, Roche, and UCB, Consultant of: AbbVie, Janssen, Lilly, Merck, Novartis, Pfizer, and UCB, Servet Akar Speakers bureau: AbbVie, Lilly, MSD, Novartis, Pfizer, Roche, Janssen, and UCB, Consultant of: AbbVie, Lilly, MSD, Novartis, Pfizer, Roche, Janssen, and UCB, Grant/research support from: AbbVie, Lilly, MSD, Novartis, Pfizer, Roche, Janssen, and UCB, Santiago Muñoz-Fernández Speakers bureau: AbbVie, BMS, Galapagos, Janssen, MSD, Novartis, Pfizer, Roche, and UCB., Consultant of: AbbVie, BMS, Galapagos, Janssen, MSD, Novartis, Pfizer, Roche, and UCB., Grant/research support from: AbbVie, BMS, Galapagos, Janssen, MSD, Novartis, Pfizer, Roche, and UCB, Hildrun Haibel Speakers bureau: AbbVie, Janssen, MSD, Pfizer, Sobi, Novartis, and Roche, Consultant of: Boehringer, Janssen, MSD, Novartis, and Roche, Torsten Diekhoff Paid instructor for: Novartis, MSD, Canon MS, Consultant of: Eli Lilly, Mikhail Protopopov: None declared, Elisabeth Altmaier Consultant of: AbbVie, Fabiana Ganz Shareholder of: Owns AbbVie stock or stock options., Employee of: AbbVie, Robert Inman Consultant of: AbbVie, Amgen, Janssen, Lilly, Novartis, Pfizer, and Sandoz, Grant/research support from: AbbVie, Amgen, and Janssen