Background: Axial spondyloarthritis (axSpA) is a chronic inflammatory disease that affects the axial skeleton and sacroiliac joints, and can be classified as ankylosing spondylitis (AS) or non-radiographic (nr)-axSpA.¹ A 2016 analysis estimated the US diagnostic prevalence of axSpA to be 0.2% and AS to be 0.1%.² Previous studies use disparate populations and diagnostic definitions;^3,4 it is therefore unclear how AS prevalence has changed over time.

Objectives: To investigate the annual diagnostic prevalence of AS in US healthcare insurance claims databases.

Methods: A retrospective, observational cohort study was conducted using 2006–2014 data from US Medicare Fee-for-Service Claims (5% random sample of all enrolled patients [pts]) and Truven MarketScan^®. Eligible pts were ≥20 years (yrs) and had ≥6 months of continuous medical and pharmacy enrolment prior to diagnosis. Diagnoses used relevant International Classification of Disease, 9^th version (ICD-9) diagnosis codes: ICD-9 720.x [x=any number] for “AS and other inflammatory spondylopathies [SpA]” or 720.0 for “AS”. Two diagnosis definitions were used: Definition 1, ≥1 relevant ICD-9 code from hospital discharge or ≥2 from rheumatologist visit; Definition 2, ≥1 relevant ICD-9 code from hospital discharge or rheumatologist visit. Annual diagnostic prevalence of SpA/AS was calculated as “number of enrolled pts who met the definition of SpA/AS within each calendar yr and had full insurance coverage (medical and pharmacy)”, divided by “total number of pts with full insurance coverage in the same yr”. A primary analysis of SpA prevalence rates used Definitions 1 and 2, followed by a sensitivity analysis for AS prevalence rates using only Definition 2. All prevalence rates are shown per 10,000 pts enrolled.

Results: The annual diagnostic prevalence of SpA appeared to increase from 2006–2014 (Table). Similarly, the sensitivity analysis showed the annual diagnostic prevalence of AS appeared to increase during the period from 2006 (Medicare: 2.87/10,000 pts [n=501,031]; MarketScan: 1.37/10,000 pts [n=17,562,637]) to 2014 (Medicare: 4.77/10,000 pts [n=1,046,107]; MarketScan: 2.14/10,000 pts [n=34,553,135]; Figure).

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Conclusion: The apparent increase in diagnostic prevalence of SpA and AS during the period from 2006–‍2014 may be a consequence of increased awareness and availability of effective treatments. Furthermore, the 2009 Assessment of SpondyloArthritis international Society development of the axSpA classification criteria to include pts with both established AS and nr-axSpA may have accelerated this increase.⁵

References: [1]Strand V. Mayo Clin Proc 2017;92:555–64;

[2]Curtis J. Perm J 2016;20:15–151;

[3]Reveille J. Arthritis Care Res (Hoboken) 2012;64:905–10;

[4]Danve A. Clin Rheumatol 2019;38:625–34;

[5]Rudwaleit M. Ann Rheum Dis 2009;68:777–83.

Acknowledgments: This study was funded by UCB Pharma. Editorial services were provided by Costello Medical.

Disclosure of Interests: Jeffrey Curtis Grant/research support from: AbbVie, Amgen, Bristol-Myers Squibb, Corona, Crescendo, Genentech, Janssen, Pfizer, Roche and UCB Pharma, Consultant of: AbbVie, Amgen, Bristol-Myers Squibb, Corona, Crescendo, Genentech, Janssen, Pfizer, Roche and UCB Pharma, Kevin Winthrop Grant/research support from: Bristol-Myers Squibb, Consultant of: AbbVie, Bristol-Myers Squibb, Eli Lilly, Galapagos, Gilead, GSK, Pfizer Inc, Roche, UCB, Benjamin Chan: None declared, Sarah Siegel: None declared, Jeffrey Stark Employee of: UCB Pharma, Robert Suruki Employee of: UCB Pharma, Rhonda Bohn Consultant of: UCB Pharma, Fenglong Xie: None declared, Huifeng Yun Grant/research support from: Bristol-Myers Squibb and Pfizer, Lang Chen: None declared, Atul Deodhar Grant/research support from: AbbVie, Eli Lilly, GSK, Novartis, Pfizer, UCB, Consultant of: AbbVie, Amgen, Boehringer Ingelheim, Bristol Myer Squibb (BMS), Eli Lilly, GSK, Janssen, Novartis, Pfizer, UCB, Speakers bureau: AbbVie, Amgen, Boehringer Ingelheim, Bristol Myer Squibb (BMS), Eli Lilly, GSK, Janssen, Novartis, Pfizer, UCB