Background/Purpose: Chronic low back pain (CLBP; back pain >3 months) with onset at age < 45 and inflammatory back pain (IBP) are regarded as early presenting and key features of axial spondyloarthritis (axSpA), and HLA-B27 as its most important genetic risk factor. Despite increasing familiarity with non-radiographic axSpA and the advent of Magnetic Resonance Imaging in demonstrating sacroiliitis, the long delay in axSpA diagnosis has not improved. The objective of this study was to explore the prevalence of CLBP and IBP in combination with HLA-B27 in the general population.

Methods: Participants of the Lifelines cohort, a large population-based cohort of the northern region of the Netherlands, filled out a questionnaire on chronic low back pain and IBP. Chronic low back pain was defined as an affirmative answer to the question ‘Did you suffer from low back pain for ≥3 months?’. IBP was questioned based on the validated European Spondyloarthropathy Study Group (ESSG) IBP criteria and was confirmed if at least 4 out of the following 5 criteria were present: (a) onset before age 45, (b) insidious onset, (c) improvement with exercise, (d) associated with morning stiffness, (e) at least 3 months duration. Participants reporting to have been diagnosed with axSpA were identified using variations of the search terms “Bechterew”, ”spondyloarthritis” and “ankylosing spondylitis”. The Illumina global screening array (GSA) beadchip-24 v1.0 was used to genotype genome-wide SNPs in a subset of Lifelines participants. HLA-B haplotypes were imputed using neighboring SNPs with HIBAG, which is an R-package, using published parameter estimates. The predicted HLA-B haplotype was considered valid if the posterior probability was >80%.

Results: 94.277 participants answered the question about CLBP, of which 22.804 (24.2%) participants reported CLBP. CLBP before the age of 45 could be identified in 17.481 (18.6%) participants. Of the 93.665 participants with ESSG questionnaire data available, 13.514 (14.4%) fulfilled the IBP criteria. HLA-B haplotype was determined with high prediction accuracy (posterior probability >0.8) in 29.399 Lifelines participants of which 2.279 (7.8%) were HLA-B27+. In the group of HLA-B27+ participants with CLBP (n=373; 23.2%), 238 (14.8%) also fulfilled the ESSG IBP criteria. Only 11 (4.6%) of these participants reported a previous axSpA diagnosis.

Conclusion: In this large Dutch population-based cohort, 7.8% were HLA-B27 positive, similar to earlier studies. Considerable underdiagnosis of axSpA may be expected since only a minor proportion of HLA-B27+ participants with CLBP fulfilling the ESSG IBP criteria reported to have been diagnosed with axSpA.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-prevalence-of-inflammatory-back-pain-and-hla-b27-in-a-large-population-based-cohort-in-the-netherlands/