Objective: The objective of this study was to investigate the diagnostic prevalence of ankylosing spondylitis (AS) and axial spondyloarthritis (axSpA) in the United States and examine treatment patterns for these diseases. Methods: This retrospective observational cohort study drew from 2006-2014 data in the US Medicare Fee-for-Service and IBM MarketScan databases. AS and axSpA diagnoses were identified through International Classification of Diseases, Ninth Revision [ICD-9] codes. Diagnostic prevalence (per 10,000 patients) was calculated as patients with AS and axSpA with full insurance coverage in each calendar year divided by the total patients with full insurance coverage in the same year. Two diagnosis definitions were used: definition 1 (D1), one or more relevant ICD-9 codes from hospital claims or two or more relevant ICD-9 codes from outpatient claims; definition 2 (D2), one or more codes from hospital/outpatient claims. Primary analyses assessed annual AS and axSpA prevalence (D1); sensitivity analyses assessed annual (D2) and 2-year prevalence. Patterns in prevalence and treatment use were analyzed descriptively; no statistical tests were performed. Results: An increase in AS prevalence (per 10,000 patients) was seen from 2006 to 2014 in primary analyses (Medicare: 2.12-3.60; MarketScan: 0.85-1.42) and sensitivity analyses. A similar trend occurred for axSpA (Medicare: 4.39-6.52; MarketScan: 1.33-2.21). For Medicare, the proportion of patients with AS (D1) using tumor necrosis factor α inhibitors (TNFis), conventional synthetic antirheumatic drugs (csARDs), nonsteroidal antiinflammatory drugs (NSAIDs), opioids, and glucocorticoids remained relatively stable; for MarketScan, TNFi-treated patients increased (51.7% to 65.7%) and NSAID-treated patients decreased (63.5% to 55.7%). Conclusion: AS and axSpA prevalence may have increased in the United States between 2006 and 2014. Reasons are unknown, but this may be due to increased disease awareness, among other factors.
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