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BackgroundBased on ASAS axial spondyloarthritis (SpA) criteria, the presence of structural changes of sacroiliac (SI) joints such as sclerosis, bone erosion, joint space widening or ankyloses dose not meet the definition of active sacroiliitis on magnetic resonance imaging (MRI), if there is no bone marrow edema (BME). However only less than half Asian patients with SpA were characterized by BME. Neither serum inflammatory markers such as c reactive protein (CRP) nor erythrocyte sedimentation rate (ESR) is able to be useful as diagnostic markers in the early phase of SpA. HLA-B27 is associated with early diagnosis of SpA and axial inflammation of SI joints on MRI. Nonetheless, HLA-B27 is not associated with structural lesions of SI joints. All factors contribute to difficult defining early Asian SpA patients in the absence of serum HLA-B27 and active imaging inflammation.ObjectivesThe aim of this study is to evaluate the prevalence of structure changes of SI joints on MRI in Taiwanese SpA patients in the absence of serum HLA-B27.MethodsThirty-three patients with inflammatory back pain and morning stiffness (disease duration more than 3 months) and high disease activity (BASDAI≥4) who had to be either serum HLA-B27 positive (10 patients) with ≥1 SpA-feature or HLA-B27 negative with ≥2 SpA-features (22 patients) were included in this prospective study. All patients did not meet the definition for a positive radiograph according to the modified New York criteria. MRI was performed with multiple sequence (Coronal and axial T1-weighted spin echo, coronal and axial short-tau inversion recovery). SI joints were evaluated for the prevalence of subchondral BME and structure changes (sclerosis, bone erosion, joint space widening and ankylosis). All patients were tested for X-rays of the pelvis and serum levels of ESR and CRP. Correlation analysis was performed among the different collected variables.ResultsSubchondral BME was only present in 8 of 23 patients with SpA in the absence of serum HLA-B27 (34.8%), while 7 of 10 (70%) HLA-B27 serum positive SpA patients had active BME on MRI. Structural changes of SI joints, including sclerosis, bone erosion and joint space widening were identified in 8 (80%), 10 (100%) and 5 (50%) SpA patients with positive serum HLA-B27, respectively. Nevertheless, these structural changes of SI joints on MRI were more common in HLA-B27 serum negative patients, as 15 (65.2%), 20 (87.0%) and 7 (30.4%) of 23 serum negative patients, respectively.ConclusionsMRI contributes to detect structural changes of SI joints for patients with nonradiographic axial SpA in the absence of serum HLA-B27.References Rudwaleit, M. & Sieper, J. Nat. Rev. Rheumatol. 2012;8, 262–268.van Tubergen, A. & Weber, U. Nat. Rev. Rheumatol. 2012;8, 253–261.van der Heijde D, et al. Ann Rheum Dis 2017;0:1–14.Turina MC, et al. RMD Open 2017;2:e000319.Baraliakos, X. & Braun, J. Nat. Rev. Rheumatol. 2013;9, 498–502.Navallas M, et al. Radiographics. 2013;33:933–56.Lambert RGW, et al. Ann Rheum Dis 2016;75:1958–1963.Chung HY, et al. An...