Background There is limited information on the epidemiology of axial spondyloarthritis (axSpA)¹ in the US. The MASTER study² described referral strategies for chronic back pain (CBP) patients (pts) who may have axSpA.

Objectives To determine the prevalence of axSpA among pts with CBP and ≥1 of 3 SpA features.

Methods PROSpA was a non-drug, interventional study conducted at rheumatology practices in the US. Eligible pts had CBP for ≥3 months that began at <45 years (yrs) of age, had ≥1 of the following SpA features: 1) positive HLA-B27, 2) current inflammatory back pain (IBP), or 3) MRI/x-ray evidence of sacroiliitis, and were not previously diagnosed with SpA. Pts were new referrals from other physicians, self-referred, or existing pts at the investigative site. Medical history/physical exam, pelvic x-ray and/or MRI of SI joints, CRP and HLA-B27 results were collected. Investigators were asked if a clinical diagnosis of axSpA could be made based upon results. In addition, data were analyzed to determine if pts fulfilled the ASAS criteria for axSpA and/or the modified New York (modNY) criteria for ankylosing spondylitis (AS) irrespective of the investigator's clinical diagnosis.

Results 751 pts enrolled at 68 sites (46% existing pts, 40% new referrals, and 14% self-referred), with IBP as the most frequent SpA feature (94%) of the 3 required for study entry. 348 (47%) pts fulfilled ASAS criteria, of whom 238 (32%) were classified as non-radiographic axSpA (nr-axSpA) (123 through the imaging arm/115 clinical arm), 108 (15%) as AS, and 2 pts had missing data. 319 (46%) were given a clinical diagnosis of axSpA by the investigator. Using the investigator's clinical diagnosis as the gold standard, the specificity and sensitivity of the ASAS criteria were 79% and 81%, respectively. Pts diagnosed with axSpA had >10 yrs of CBP (Table). Overall, a lower proportion of males and HLA-B27 positivity was noted among those classified as AS compared to published data for a typical AS population.

Conclusions Among pts with CBP for ≥3 months that began at age <45 yrs, the presence of ≥1 of 3 SpA features appears to be an effective way to identify potential axSpA pts. The ASAS criteria performed well in this US cohort. The lower than expected proportion of males and HLA-B27 positivity is possibly because such pts with axSpA are more readily diagnosed in clinical practice and were not eligible for this study.

References

1. Reveille JD et al. Arthritis Care Res (Hoboken) 2012.

2. Poddubnyy D et al. J Rheum 2011.

Acknowledgements AbbVie Inc. sponsored the study, contributed to its design, and participated in the collection, analysis, and interpretation of the data, and in the writing, reviewing, and approval of the final version. Medical writing support was provided by Jessica L. Suboticki, PhD, of AbbVie Inc.

Disclosure of Interest : A. Deodhar Grant/research support: AbbVie, Amgen, Novartis, UCB, Consultant for: AbbVie, Merck-Sharp-Dohme, Pfizer and UCB, Speakers bureau: AbbVie, Merck-Sharp-Dohme, Pfizer and UCB, P. Mease Grant/research support: AbbVie, Amgen, BiogenIdec, Bristol-Myers Squibb, Genentech, GlaxoSmithKline, Janssen Lilly, Merck, Merck-Serono, Novartis, Novo-Nordisk, Pfizer, Roche, UCB, and Vertex, Consultant for: AbbVie, Amgen, BiogenIdec, Bristol-Myers Squibb, Genentech, GlaxoSmithKline, Janssen Lilly, Merck, Merck-Serono, Novartis, Novo-Nordisk, Pfizer, Roche, UCB, and Vertex, Speakers bureau: AbbVie, Amgen, BiogenIdec, Bristol-Myers Squibb, Genentech, GlaxoSmithKline, Janssen Lilly, Merck, Merck-Serono, Novartis, Novo-Nordisk, Pfizer, Roche, UCB, and Vertex, J. Reveille Consultant for: AbbVie and UCB, J. Curtis Grant/research support: Janssen, Amgen, AbbVie, UCB, CORRONA, Crescendo, BMS, Roche/Genentech, Pfizer, Celgene, Medimmune, Consultant for: Janssen, Amgen, AbbVie, UCB, CORRONA, Crescendo, BMS, Roche/Genentech, Pfizer, Celgene, Medimmune, P. Karunaratne Shareholder of: AbbVie, Employee of: AbbVie, K. Malhotra Shareholder of: AbbVie, Employee of: AbbVie, A. Pangan Shareholder of: AbbVie, Employee of: AbbVie

DOI 10.1136/annrheumdis-2014-eular.1135