Background Unacceptable diagnostic delay in axial Spondyloarthritis (axSpA) remains an issue. In 2009, the longitudinal SPondyloArthritis Caught Early (SPACE)-cohort started to assess the prevalence of axSpA and the reliability of an early diagnosis in patients with chronic back (CBP) of unknown origin. Here we present one of the main outcomes of SPACE.

Objectives To assess the two-year (2y) prevalence of an axSpA diagnosis among patients with recent onset CBP referred to the rheumatologist; To investigate the sustainability of a baseline (BL) diagnosis of axSpA when reviewed after 2y; And to explore patient-differences between BL and 2y, in those with and without an axSpA diagnosis.

Methods We analysed the 2y data from SPACE, a European inception cohort of patients (age <45y) with CBP of recent onset (≥3 months, ≤2y) and unknown origin. The full diagnostic work-up included all clinical SpA-features, acute phase reactants, HLA-B27, radiographs and MRI of the sacroiliac joints (SI-CR and SI-MRI) and spine (data not shown). Patients with increased likelihood of having axSpA (≥1 major or ≥2 minor prespecified SpA-features) were eligible for follow-up with the remaining patients excluded per protocol. The clinical diagnosis at 2y was the main outcome of this study. At each visit, the treating rheumatologist judged on the presence or absence of axSpA (axSpA or no-axSpA) with a level of confidence (LoC) on a numeric rating scale (0: not confident at all to 10: very confident). The main outcome was the presence of ‘definite axSpA’ at 2y, defined as a clinical diagnosis of axSpA with a LoC ≥7 (complete follow-up) or at the two last available visits if 2y visit was missing. ‘No axSpA’ was defined as not having axSpA at 2y (with LoC ≥7; or if LoC <7, plus an alternative diagnosis for CBP reported). All other patients were considered having an ‘uncertain’ diagnosis. The ASAS classification criteria were computed using sacroiliitis central reading results in definite axSpA patients. We assessed the prevalence of definite axSpA at 2y as well as changes in diagnosis over time, and descriptively summarised BL characteristics.

Results A total of 555 CBP patients were included (Leiden n=383, Oslo n=97, Amsterdam n=48, and Gouda n=27). A diagnosis of definite axSpA was given to 175 (32%) patients at BL and 166 (30%) at 2y (Figure 1). The mean (SD) LoC’s were 8.1 (2.0) and 8.7 (1.0), with 155/175 (89%) and 145/166 (87%) fulfilling ASAS classification criteria, respectively. BL diagnostic judgments were relatively unequivocal and remained rather stable: At 2y, 6% of the BL diagnoses of definite axSpA were refuted; and -vice versa: 9% of those who did not obtain a BL diagnosis of axSpA ‘gained’ one at 2y. Residual diagnostic uncertainty remained in 14% of CBP-patients. Expectedly, BL SpA-related features were more prevalent in the 2y definite axSpA group (Table 1). (The presence or absence of) imaging-detected sacroiliitis at BL appeared the best discriminator between axSpA and no axSpA at 2y.

Conclusion One third of patients with CBP of recent onset referred to the rheumatologist has definite axSpA. Most of these patients can be unequivocally and reliably diagnosed at their first assessment. None of the many SpA-features suffices alone, but imaging discriminates best.

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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, Janssen, 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.