Background We have shown in the SPACE cohort that a diagnosis of early axial spondyloarthritis (axSpA) can be made in patients with chronic back pain (CBP) of less than two years (2y). However, diagnostic uncertainty can be an obstacle towards initiating disease-modifying treatment. The value of repeated assessments of SpA features for a definite clinical diagnosis is yet to be determined.

Objectives To assess the yield of repeated assessments of SpA features over 2y to make a definite axSpA diagnosis in patients with recent onset CBP referred to the rheumatologist, and to describe the characteristics of patients that change to definite axSpA over time.

Methods We used the 2y data from the SPACE cohort, a European multicentre inception cohort of patients (age <45y) with CBP of recent onset (≥3 months, ≤2y) included from 2009 to 2016. The diagnostic work-up consisted of patient history, physical examination, acute phase reactants (APR) and HLA-B27 testing, radiographs and MRI of the sacroiliac joints (SI-CR and SI-MRI) and spine (not shown). In patients with ≥1 major or ≥2 minor prespecified SpA features, clinical assessments, APR, and imaging were repeated at 1y and 2y visits. At each visit, the rheumatologist reported a clinical diagnosis of axSpA or no axSpA with level of confidence (LoC; numeric rating scale from 0 (not confident at all) to 10 (very confident)). Herein, we categorized patients by diagnosis likelihood. At baseline (BL), two categories were defined: ‘Definite axSpA/no axSpA’ when the diagnosis was given with a LoC ≥7 and ‘Uncertain axSpA/no axSpA’ if LOC <7. At 2y, the following categories were defined: ‘definite, most likely and possible axSpA’ and ‘possible, most likely and definite no axSpA’ (Figure 1). The ASAS classification criteria were applied using central reading. We explored the diagnostic course over 2y. In patients shifting from no axSpA (definite or uncertain) or uncertain axSpA at BL to definite axSpA at 2y, SpA features were investigated over time.

Results We included 552 patients. Definite axSpA was attributed to 175 (32%) patients at BL and 166 (30%) at 2y (Figure 1); 155/175 (89%) and 145/166 (87%) fulfilled ASAS classification criteria, respectively. Of the 175 patients with definite axSpA at BL, 133 retained the diagnosis, and only 13 changed to no axSpA at 2y. Although still considered as axSpA by the rheumatologist, 29 definite axSpA patients at BL were no longer definite axSpA at 2y, due to decrease in LOC to <7 (n=14) or incomplete follow-up (n=15). Overall, the diagnosis changed to definite axSpA over 2y in 33 patients (BL: 16 uncertain axSpA, 12 uncertain no axSpA, and 5 definite no axSpA); on average, 3 SpA features were already present at BL and 1 to 2 new SpA features developed over 2y (Table 1), with response to NSAIDs and MRI sacroiliitis being the most frequently captured over time.

Conclusion The yield of repeated assessments of SpA features in patients with CBP suspected of axSpA was modest for the new definite axSpA diagnosis at 2y. Most SpA features were already present at BL, with imaging findings and response to NSAIDs appearing as frequent incident SpA features potentially adding to a definite axSpA diagnosis over time.

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REFERENCES: NIL.

Acknowledgements: NIL.

Disclosure of Interests Mary Lucy Marques: None declared, Sofia Ramiro Consultant of: AbbVie/Abbott, Eli Lilly, Galapagos, Merck/MSD, Novartis, Pfizer, UCB, Sanofi, Miranda van Lunteren: None declared, Rosalinde Stal: None declared, Inger Jorid Berg: None declared, Karen Minde Fagerli: None declared, M. van Oosterhout: None declared, Sofia Exarchou: None declared, Roberta Ramonda: None declared, Marleen G.H. van de Sande Speakers bureau: Novartis, UCB, Janssen, Consultant of: Novartis, UCB, Abbvie, Eli Lily, Grant/research support from: Novartis, UCB, Eli Lilly, Robert B.M. Landewé Consultant of: Abbott, Amgen, AstraZeneca, BMS, GSK, Novartis, Merck, Pfizer, Schering-Plough, UCB Pharma, Imaging Rheumatology bv, Désirée van der Heijde Consultant of: AbbVie, Bayer, BMS, Cyxone, Eisai, Galapagos, Gilead, Glaxo-Smith-Kline, Jansen, Novartis, Pfizer, UCB, Lilly, Imaging Rheumatology bv, Floris A. van Gaalen Consultant of: Stichting vrienden van Sole Mio, Stichting ASAS, Jacobus stichting, Novartis, UCB, MSD, AbbVie, Bristol Myers Squibb, Eli Lilly.