POS0921 INFLUENCE OF HLA-B27 STATUS ON MR IMAGING FINDINGS IN PATIENTS WITH LOW BACK PAIN

Background The knowledge of factors influencing the susceptibility to and extent of changes at the sacroiliac joints (SIJs) are of great importance in the understanding of pathophysiological processes in axial spondyloarthritis (axSpA)[1]. Recent studies showed that previous delivery and the HLA-B27 status have a special role in the expression of bone marrow edema at the SIJs in the general population. Furthermore, the influence of HLA-B27 differed in men and women[1 2]. Objectives The aim of this study was to investigate the sex-specific influence of the HLA-B27 status on the SIJ lesions such as ankylosis, erosion, fat metaplasia and bone marrow edema and its distribution and extent in patients with low back pain of non-inflammatory origin. Methods In this post-hoc analysis, 139 patients (90 women and 49 men) with low back pain of mechanical/ non-inflammatory origin (after exclusion of axSpA) were included. The MR images of the sacroiliac joints were scored by two trained readers separately for the presence of axSpA features: ankylosis, erosions, sclerosis, fat metaplasia and bone marrow edema. The scoring was performed for the three SIJ regions (ventral/middle/dorsal) differentiated for the sacral and iliac sides. Frequencies of lesions per joint region were compared between HLA-B27 positive and negative individuals using Chi-squared tests. Extent of lesions, expressed as sum scores were compared using T-tests. All analyses were carried out for the entire group and for men and women separately. Results A total of 90 women and 49 men were included in this post-hoc-analysis. HLA-B27 was positive in 33/90 women (36.7%), while this was the case in 23/49 men (46.9%) (further clinical data is given in Table 1). There was no difference in frequency of overall occurrence of erosion (22.9% vs. 16.1%; p = 0.392), sclerosis (48.2% vs. 48.2%; p > 0.999), fat metaplasia (12.0% vs. 7.1%; p = 0.403), bone marrow edema (28.9% vs. 32.1%; p = 0.710) and ankylosis (2.4% vs. 3.6%; p > 0.999) between HLA-B27 negative and positive individuals, respectively. A detailed graphical representation of spatial distribution of lesion within the joint is given in Figure 1. Conclusion In our cohort of pre-selected patients with chronic low back pain and after exclusion of axSpA, the HLA-B27 status did not determine extent or pattern of imaging lesions in either men or women. These results somewhat contradict previously published data on healthy volunteers. This indicates that further studies are needed especially in the investigation of the sex-specific influence of HLA-B27 status on imaging lesions. References [1]Baraliakos X, Richter A, Feldmann D, et al. Which factors are associated with bone marrow oedema suspicious of axial spondyloarthritis as detected by MRI in the sacroiliac joints and the spine in the general population? Ann Rheum Dis 2021;80(4):469-74. doi: 10.1136/annrheumdis-2020-218669 [published Online First: 20201125] [2]Braun J, Baraliakos X, Bulow R, et al. Striking sex differences in magnetic resonance imaging findings in the sacroiliac joints in the population. Arthritis Res Ther 2022;24(1):29. doi: 10.1186/s13075-021-02712-7 [published Online First: 20220120] Acknowledgements: NIL. Disclosure of Interests Sevtap Tugce Ulas Grant/research support from: STU reports funding from the Berlin Institute of Health (BIH) during the conduct of this study (Junior Digital Clinician Scientist Programme)., Fabian Proft Speakers bureau: FP reports grants and personal fees from Novartis, Lilly and UCB, as well as personal fees from AbbVie, AMGEN, BMS, Hexal, Janssen, MSD, Pfizer and Roche., Grant/research support from: FP reports grants and personal fees from Novartis, Lilly and UCB, as well as personal fees from AbbVie, AMGEN, BMS, Hexal, Janssen, MSD, Pfizer and Roche., Torsten Diekhoff Speakers bureau: TD reports personal fees from MSD, Novartis and Eli Lilly., Grant/research support from: TD reports funding from the Berlin Institute of Health (BIH) during the conduct of this study., Valeria Rios Rodriguez Speakers bureau: VRR reports personal fees from AbbVie and Falk e.V., Judith Rademacher Grant/research support from: JR reports funding from the Berlin Institute of Health (BIH) during the conduct of this study (Clinician Scientist Programme)., Mikhail Protopopov Speakers bureau: MP reports personal fees from UCB and Novartis., Denis Poddubnyy Speakers bureau: DP reports personal fees from AbbVie, Eli Lilly, MSD, Novartis, Pfizer, Bristol-Myers Squibb, Roche, UCB, Biocad, GlaxoSmithKline and Gilead outside the submitted work., Grant/research support from: DP reports grants from AbbVie, Eli Lilly, MSD, Novartis, Pfizer and personal fees from Bristol-Myers Squibb, Roche, UCB, Biocad, GlaxoSmithKline and Gilead outside the submitted work., Katharina Ziegeler Grant/research support from: KZ reports funding (research grant) from the Assessment of Spondyloarthritis international Society (ASAS) during the conduct of this study.

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