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Objectives: To assess the association of posterior element (PE) and facet joint (FJ) inflammation with subsequent new FJ ankylosis (FJA) on MRI, in patients with radiographic axial spondyloarthritis (r-axSpA)., Methods: Patients from the Sensitive Imaging in Ankylosing Spondylitis cohort, inclusion criteria r-axSpA and ≥1 radiographic spinal syndesmophyte, were studied. MRI of the full spinal was performed at baseline, 1 and 2 years. PE/FJ inflammatory lesions and FJA were assessed per vertebral unit (VU) level by three readers. With multilevel time-lagged autoregressive generalised estimated equations, the association between PE/FJ inflammation and the subsequent development of FJA was investigated, taking the reader and VU levels into account., Results: Out of the 58 patients with at least 2 reader scores available, mean age 49 (SD 10) years, 84% men, 59% had baseline PE inflammation, 24% had FJ inflammation and 26% had FJA. PE inflammation was more prevalent in the lower thoracic spine and FJ inflammation in the upper thoracic spine. VU with PE or FJ inflammation showed subsequent new FJA in two and one VU levels, respectively. The probability of developing FJA doubled with prior FJ inflammation. In multilevel analysis, FJ inflammation was associated with subsequent FJA (OR=3.8, 95% CI: 1.5 to 9.8), while no association was found between PE inflammation and new FJA (OR=1.2 (0.6-2.4))., Conclusions: FJ inflammation is rare in severe r-axSpA, but when present, the likelihood of developing subsequent FJA is over three times higher compared with FJ without inflammation. This finding contributes to the understanding of the relationship between inflammation and ankylosis at the same anatomical location in patients with axSpA., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2024. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

Background: The Computed Tomography Syndesmophyte Score (CTSS) was developed as a reliable and sensitive tool to assess syndesmophytes in low-dose CT images of the entire spine in patients with axial spondyloarthritis (axSpA). The original paper provided sparce examples of the CTSS grades., Objectives: Provide an atlas tailored to assist readers in understanding and employing the CTSS method., Methods: In this paper, illustrations of the different grades and views of the CTSS are presented. CTSS is used to measure bone formation in the spine of patients with axial spondyloarthritis (axSpA), in the form of syndesmophytes. In both the sagittal and coronal planes, syndesmophytes can be graded from 0 to 3 over 23 vertebral units starting at C2 and ending at S1. The CTSS ranges from 0 (absence of axSpA-related syndesmophytes) to 552 (total ankylosis of the spine)., Results: The current atlas contains low-dose CT images of the spine without lesions (for reference) and all grades of syndesmophytes in different planes used in the CTSS. Examples are arranged per spinal segment (cervical, thoracic and lumbar)., Conclusions: These images can be used to assist any reader in the assessment of syndesmophytes on (low-dose) CT in patients with axSpA., Competing Interests: Competing interests: MLM — none. SR: Research Grants — AbbVie, Galapagos, MSD, Novartis, Pfizer, UCB. Consultancy — AbbVie, Eli Lilly, Janssen, MSD, Novartis, Pfizer, Sanofi, UCB. DvdH: Consultancy — AbbVie, ArgenX, Bayer, BMS, Cyxone, Eisai, Galapagos, Gilead, Glaxo-Smith-Kline, Janssen, Lilly, Novartis, Pfizer, Takeda, UCB Pharma. Director of Imaging Rheumatology bv. MR: Consultancy — ASAS-group. TD: Grants/support — Canon Medical Systems and ASAS-group. Speaker’s bureau — Canon Medical Systems, Novartis, MSD, BioCad, UCB and Roche. Consultancy — Lilly. K-GAH: lecture honoraria — AbbVie, Lilly, MSD, Novartis, and Pfizer. Consultancy — AbbVie. Co-founder of BerlinFlame GmbH. FAvG: Research Grants — Novartis. Consultancy — MSD, AbbVie, Novartis and BMS. MdH: Consultancy and support for attending conferences — UCB., (© Author(s) (or their employer(s)) 2024. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

Objectives: To determine how much of the effect of vertebral corner inflammation on development of syndesmophytes is explained by vertebral corner fat deposition., Methods: Patients with radiographic axial spondyloarthritis (r-axSpA) from the SIAS (Sensitive Imaging in Ankylosing Spondylitis) cohort and ASSERT (Ankylosing Spondylitis Study for the Evaluation of Recombinant Infliximab Therapy) trial were assessed at T0, T1 (SIAS: 1 year; ASSERT: 24 weeks) and T2 (2 years). Syndesmophytes assessed in each vertebral corner by whole spine low-dose CT (SIAS) or spinal radiographs (ASSERT) at T0 and T2 were considered present if seen by two of two readers. Inflammation (T0) and fat deposition (T0 and T1) on MRI were present if seen by ≥2 of 3 readers (SIAS) or 2 of 2 readers (ASSERT). Vertebral corners showing fat deposition or a syndesmophyte at baseline were ignored. Mediation analysis was applied to determine what proportion of the total effect of inflammation on syndesmophyte formation could be explained via the path of intermediate fat deposition., Results: Forty-nine SIAS patients (with 2667 vertebral corners) and 168 ASSERT patients (with 2918 vertebral corners) were analysed. The presence of inflammation at T0 increased the probability of a new syndesmophyte in the same vertebral corner at T2 by 9.3%. Of this total effect, 0.2% (2% (0.2 of 9.3) of the total effect) went via intermediate new fat deposition. In ASSERT, the total effect was 7.3%, of which 0.8% (10% of the total effect) went via new fat deposition., Conclusion: In r-axSpA, vertebral corner inflammation may lead to syndesmophyte formation but in a minority of cases via visible fat deposition., Competing Interests: Competing interests: AS—honoraria from Novartis, support for meetings from Lilly and UCB. DvdH—grant from Dutch Rheumatism Association; consulting fees from AbbVie, Gilead, Glaxo-Smith-Kline, Lilly, Novartis and UCB Pharma; other interest as director of Imaging Rheumatology. FAvG—grants from Stichting vrienden van Sole Mio, Stichting ASAS, Jacobus stichting, Novartis and UCB; consulting fees from Novartis, MSD, AbbVie, Bristol Myers Squibb and Eli Lilly. MdH—grants from FWRO/FRSR; participation in data safety monitoring board for UCB; member of EULAR Advocacy Committee, Young ASAS leader and ASAS-EULAR taskforce. MR—fees for ASAS CLASSIC Study. PMM—consulting fees from AbbVie, BMS, Celgene, Eli Lilly, Galapagos, Janssen, MSD, Novartis, Orphazyme, Pfizer, Roche and UCB. RL—consulting fees from AbbVie, Amgen, BMS, GSK, Janssen, Eli Lilly, Novartis, Pfizer and UCB; honoraria from AbbVie, Amgen, BMS, GSK, Janssen, Eli Lilly, Novartis, Pfizer and UCB; participation in data safety monitoring board for UCB; chair of quality of care for EULAR. SR—grants from AbbVie, Galapagos, MSD, Novartis, Pfizer and UCB; consulting fees from AbbVie, Eli Lilly, MSD, Novartis, Pfizer, UCB and Sanofi; honoraria from Eli Lilly, MSD, Novartis and UCB. JB, RS, RvdB, XB—nothing to declare., (© Author(s) (or their employer(s)) 2023. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

Objectives: To assess construct validity of the CT Syndesmophyte Score (CTSS) for the measurement of structural spinal damage in patients with radiographic axial spondyloarthritis., Methods: Low-dose CT and conventional radiography (CR) were performed at baseline and 2 years. CT was assessed with CTSS by two readers and CR with modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS) by three readers. Two hypotheses were tested: (1) syndesmophytes scored with CTSS are also detected with mSASSS at baseline or 2 years later; (2) CTSS is non-inferior to mSASSS in correlations with spinal mobility measures. Presence of a syndesmophyte was determined per reader per corner for all anterior cervical and lumbar corners on CT at baseline and CR at baseline and 2 years. Correlations of CTSS and mSASSS with six spinal/hip mobility measurements plus Bath Ankylosing Spondylitis Metrology Index (BASMI) were tested., Results: Data from 48 patients (85% male, 85% HLA-B27+, mean age 48 years) were available for hypothesis 1 and 41/48 were available for hypothesis 2. At baseline, syndesmophytes were scored with CTSS in 348 (reader 1, 38%) and 327 (reader 2, 36%) corners out of 917. Of these, depending on reader pairs, 62%-79% were also seen on CR at baseline or after 2 years. CTSS correlated well ( r s 0.46-0.73), and with higher correlation coefficients than mSASSS ( r s 0.34-0.64), with all spinal mobility measures and BASMI., Conclusions: The good agreement between syndesmophytes detected by CTSS and mSASSS and the strong correlation of CTSS with spinal mobility support the construct validity of the CTSS., Competing Interests: Competing interests: DvdH: grant from Dutch Rheumatism Association, consulting fees from AbbVie, Gilead, Glaxo-Smith-Kline, Lilly, Novartis and UCB Pharma, Other interest as director of Imaging Rheumatology bv; FAvG: grants from Stichting vrienden van Sole Mio, Stichting ASAS, Jacobus stichting, Novartis and UCB, consulting fees from Novartis, MSD, AbbVie, Bristol Myers Squibb and Eli Lilly; MR: fees for ASAS CLASSIC study; SR: grants from AbbVie, Galapagos, MSD, Novartis, Pfizer and UCB, consulting fees from AbbVie, Eli-Lilly, MSD, Novartis, Pfizer, UCB and Sanofi, honoraria from Eli-Lilly, MSD, Novartis and UCB; JB, RS, RvdB and XB: nothing to declare., (© Author(s) (or their employer(s)) 2023. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

Objective: To investigate whether in radiographic axial spondyloarthritis (r-axSpA) inflammation is associated with lower trabecular bone density (TBD), and subsequently, if a lower TBD increases the likelihood of 2-year bone formation at the same vertebra., Methods: Whole spine (C3-L5) data from patients included in the multicentre 2-year Sensitive Imaging in Ankylosing Spondylitis cohort was used. Two readers measured baseline TBD by Hounsfield units (HU) on low-dose CT (ldCT). Baseline MRI bone marrow oedema (BME) status scores and ldCT syndesmophyte formation and/or growth change-from-baseline scores were assessed by three and two readers, respectively. Average of readers' continuous measurements or readers' agreement in binary scores generated within the same vertebra (1-present in ≥1 quadrant/0-absent in all quadrants) were used. Multilevel generalised estimating equations models were used, the unit of analysis being the vertebra., Results: In 50 patients with r-axSpA, TBD HU decreased from cranial to caudal vertebrae. Baseline MRI-BME was present in 300/985 (30%) and syndesmophytes in 588/910 (65%) vertebrae, both most prevalent at thoracolumbar region. Syndesmophyte formation or growth was observed in 18% of at-risk vertebrae (124/691). A significant confounder-adjusted association was found between inflammation and lower TBD (regression coefficient=-51; 95% CI-63 to -39). TBD was not associated with 2-year syndesmophyte formation or growth (adjusted OR 1.00; 95% CI 0.99 to 1.00)., Conclusion: In r-axSpA, while vertebral inflammation was associated with lower vertebral TBD, lower vertebral TBD itself did not increase the risk for new bone formation at the same vertebra. In preventing syndesmophyte progression, targeting local inflammation seems more important than targeting vertebral trabecular bone loss., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2023. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

Objectives: To investigate the associations between MRI detected vertebral corner inflammation (VCI) and vertebral corner fat deposition (VCFD) on whole spine low-dose CT scan (ldCT) detected syndesmophyte formation and growth., Methods: Patients from the Sensitive Imaging in Ankylosing Spondylitis cohort underwent MRI (baseline, 1 year and 2 years) and ldCT (baseline and 2 years). MR images were scored by three readers for VCI and VCFD, MRI patterns were defined by presence of VCI and/or VCFD over 2 years. LdCT images were scored by two central readers for presence and size of syndesmophytes and change was calculated for new or new/grown syndesmophytes. Multilevel generalised estimated equations were used to test the associations between VCI and VCFD and syndesmophyte development., Results: Fifty radiographic patients with axial spondyloarthritis were included (mean age 49 years, 86% male, 78% HLA-B27+). Absence of both VCI and VCFD protected against syndesmophyte development (ORs 0.36-0.37). Presence of VCI and/or VCFD increased the risk of syndesmophyte development (ORs 1.73-2.60). Out of all corners with a new or new/grown syndesmophyte, 47% of corners according to reader 1 and 44% according to reader 2 had neither VCI nor VCFD preceding the bone formation., Conclusions: VCI and VCFD were positively associated with syndesmophyte development. This has been shown for the first time for syndesmophytes detected on ldCT and also in the thoracic spine. However, almost half of all bone formation occurred in corners without VCI or VCFD, suggesting the presence of these lesions in yearly MRIs does not fully clarify the development of syndesmophytes., Competing Interests: Competing interests: AS reports consulting fees from UCB, payment from Novartis and support for attending meetings from Lilly and UCB; DvdH reports financial support from the Dutch Rheumatism Association for the Sensitive Imaging in Ankylosing Spondylitis Study, consulting fees from AbbVie, Gilead, GlaxoSmithKline, Lilly, Novartis and UCB and is a Director of Imaging Rheumatology BV; FAvG reports grants from Stichting Vrienden van Sole Mio, Stichting ASAS, Jacobus Stichting, Novartis and UCB, fees from Novartis and personal fees from MSD, AbbVie, Bristol Myers Squibb and Eli-Lilly; MR reports grants for the ASAS CLASSIC Study, outside the submitted work; RL reports consulting fees and speaker honoraria from AbbVie, Amgen, BMS, GSK, Janssen, Eli-Lilly, Novartis, Pfizer and UCB, participation on the data safety monitoring board for a trial outside the submitted work and is a Chair of Quality of Care for EULAR; SR reports grants from AbbVie, Galapagos, MSD, Novartis, Pfizer and UCB, consulting fees from AbbVie, Eli Lilly, MSD, Novartis, Pfizer, UCB and Sanofi and payment/honoraria for lectures/presentations from Eli Lilly, MSD, Novartis and UCB., (© Author(s) (or their employer(s)) 2022. Re-use permitted under CC BY. Published by BMJ.)

Objective: Studying vertebral bone loss in radiographic axial spondyloarthritis (r-axSpA) has been challenging due to ectopic bone formation. We cross-sectionally analysed low-dose CT (ldCT) trabecular bone density Hounsfield units (HU) measurements and calculated inter-reader reliability at the vertebral level in patients with r-axSpA., Methods: LdCT scans of 50 patients with r-axSpA from the sensitive imaging in ankylosing spondylitis study, a multicentre 2-year prospective cohort were included. Trabecular bone HU taken from a region of interest at the centre of each vertebra (C3-L5) were independently assessed by two trained readers. HU mean (SD), and range were provided at the vertebral level, for each reader and centre separately. Inter-reader reliability and agreement were assessed using intraclass correlation coefficients (ICC; single measurements, absolute agreement, two-way mixed effects models); smallest detectable difference and Bland-Altman plots., Results: Overall, 1100 vertebrae were assessed by each reader. HU values decreased from cranial to caudal vertebrae. For readers 1 and 2 respectively, the highest mean (SD) HU value was obtained at C3 (354(106) and 355(108)), and the lowest at L3 (153(65) and 150 (65)). Inter-reader reliability was excellent (ICC(2,1):0.89 to 1.00). SDD varied from 4 to 8. For most vertebrae, reader 1 scored somewhat higher than reader 2 (mean difference of scores ranging from -0.6 to 2.9 HU). Bland-Altman plots showed homoscedasticity., Conclusion: LdCT measurement of HU is a feasible method to assess vertebral bone density in r-axSpA with excellent inter-reader reliability from C3 to L5. These results warrant further validation and longitudinal assessment of reliability., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2022. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

Objective: MRI depicts inflammation and structural damage in rheumatoid arthritis (RA). The validity of MRI-scoring of wrist-joints and metacarpophalangeal-joints according to the RA MRI score(RAMRIS) has been demonstrated. The Outcomes in Rheumatology Clinical Trials (OMERACT) RAMRIS Working Group recently called for validation of the RAMRIS of the metatarsophalangeal (MTP)-joints. Therefore, a systematic literature review was performed to test if the RAMRIS applied to the MTP-joints meets the OMERACT Filter of Truth, Discrimination and Feasibility., Methods: Medical literature databases up to January 2018 were systematically reviewed for studies reporting on RAMRIS applied to MRI of the MTP-joints in RA. To be included, an article had to contain at least one MRI-feature (synovitis, bone marrow oedema (BME), tenosynovitis, erosion, joint space narrowing (JSN)) and one item from the OMERACT Filter: Truth (face, content and construct validity), Discrimination (test-retest reliability, ability to discriminate in trials, longitudinal construct validity and thresholds of meaning) and Feasibility., Results: Of the 749 retrieved studies, 13 were included, of which 9 provided data on construct validity, 4 on discrimination (3 on reliability, 2 on longitudinal construct validity and 1 on ability to discriminate in trials) and none on feasibility. Construct validity was suggested for BME and erosions, but lacking for synovitis, tenosynovitis and JSN. Data for discrimination remain to be developed for all outcomes., Conclusion: According to the OMERACT Filter, the validity of the RAMRIS of the forefeet is insufficient in different aspects. A research agenda was determined., Competing Interests: Competing interests: None declared.

In 2003, the Nobel Prize for Medicine was awarded for contribution to the invention of MRI, reflecting the incredible value of MRI for medicine. Since 2003, enormous technical advancements have been made in acquiring MR images. However, MRI has a complicated, accident-prone dark side; images are not calibrated and respective images are dependent on all kinds of subjective choices in the settings of the machine, acquisition technique parameters, reconstruction techniques, data transmission, filtering and postprocessing techniques. The bright side is that understanding MR techniques increases opportunities to unravel characteristics of tissue. In this viewpoint, we summarise the different subjective choices that can be made to generate MR images and stress the importance of communication between radiologists and rheumatologists to correctly interpret images., Competing Interests: Competing interests: None declared.

Objectives: To describe the prevalence of degenerative changes on MRI and conventional radiographs of the spine in a young population with suspicion of axial spondyloarthritis (axSpA) and assess whether it is possible to discriminate between degenerative changes and lesions associated with axSpA., Methods: Whole spine MRI and cervical and lumbar radiographs of patients ≥18 years with chronic back pain (≥3 months, ≤3 years, onset <50 years) were assessed for degeneration by two readers, and for SpA lesions by two other readers, all blinded for clinical information and results of the other readers. Degenerative scores were adjudicated in case of disagreement (by a third reader). Patients fulfilling and not fulfilling the Assessment of SpondyloArthritis international Society axSpA criteria were compared for prevalence of degenerative lesions. Scores for degenerative and SpA lesions were compared, and overlap was defined as the presence of both types of lesions in a single vertebral unit (VU)., Results: In 456/648 (70.4%) patients (46.8% men, mean age 33.6), degenerative lesions were found with similar percentages in patients with no axSpA and with axSpA (72.4% and 69.2%, p=0.45). Modic changes were found more often in patients with no axSpA (29/239, 12.1%) versus patients with axSpA (19/409, 4.6%, p=0.01). Other lesions were evenly distributed. Overlap was minimal in 19 patients (3.0%) and 32/14 674 (0.2%) VUs for SpA reader 1 and in 23 patients (3.6%) and 34/14 674 VUs (0.2%) for SpA reader 2., Conclusion: The prevalence of degeneration is high in an early inflammatory back pain cohort. Discrimination between degeneration and axSpA lesions is very well possible with little overlap between degenerative and axSpA readings., Competing Interests: Competing interests: None declared.

This paper presents an atlas for the Outcome Measures in Rheumatology Clinical Trials (OMERACT) thumb base osteoarthritis MRI scoring system (TOMS). The atlas includes reference images of each grade of each feature that is assessed in TOMS (synovitis grade 0-3, subchondral bone defects grade 0-3, osteophytes grade 0-3, cartilage assessment grade 0-3, subluxation and bone marrow lesions grade 0-3) in the first carpometacarpal and scapho-trapezio-trapezoid joint. The presented reference images can be used to guide scoring of thumb base MRIs in patients with hand osteoarthritis according to the OMERACT TOMS., Competing Interests: Competing interests: None declared.

Objectives: Moderate alcohol consumption is protective against rheumatoid arthritis (RA) development and associated with lower levels of systemic inflammation in RA and in the general population. We therefore hypothesised that moderate alcohol consumption is associated with less severe local inflammation in joints in RA, detected by MRI. Since asymptomatic persons can have low-grade MRI-detected inflammation, we also hypothesised that alcohol consumption is associated with the extent of MRI inflammation in asymptomatic volunteers., Methods: 188 newly presenting patients with RA and 192 asymptomatic volunteers underwent a unilateral contrast-enhanced 1.5T MRI of metacarpophalangeal, wrist and metatarsophalangeal joints. The MRIs were scored on synovitis, bone marrow oedema and tenosynovitis; the sum of these yielded the MRI inflammation score. MRI data were evaluated in relation to current alcohol consumption, categorised as non-drinkers, consuming 1-7 drinks/week, 8-14 drinks/week and >14 drinks/week. Association between C reactive protein (CRP) level and alcohol was studied in 1070 newly presenting patients with RA., Results: Alcohol consumption was not associated with the severity of MRI-detected inflammation in hand and foot joints of patients with RA (P=0.55) and asymptomatic volunteers (P=0.33). A J-shaped curve was observed in the association between alcohol consumption and CRP level, with the lowest levels in patients consuming 1-7 drinks/week (P=0.037)., Conclusion: Despite the fact that moderate alcohol consumption has been shown protective against RA, and our data confirm a J-shaped association of alcohol consumption with CRP levels in RA, alcohol was not associated with the severity of joint inflammation. The present data suggest that the pathophysiological mechanism underlying the effect of alcohol consists of a systemic effect that might not involve the joints., Competing Interests: Competing interests: None declared.

Introduction: A phase of arthralgia may precede the emergence of rheumatoid arthritis (RA). Although several studies have focused on biomarkers, the relevance of this phase for patients is less studied. It is unknown if patients already have functional limitations and if this is correlated to the extent of subclinical inflammation. Therefore, we assessed functional disability in patients with clinically suspect arthralgia (CSA), its association with MRI-detected subclinical inflammation and its course during progression to clinical arthritis., Methods: From April 2012 to March 2015, 241 patients had arthralgia for <1 year and were, based on clinical presentation, considered at risk for RA by their rheumatologists. At baseline, Health Assessment Questionnaire (HAQ) scores were determined and unilateral 1.5 T MRI of metacarpophalangeal, wrist and metatarsophalangeal joints were made. Presence of MRI-detected subclinical inflammation was assessed by summing synovitis, tenosynovitis and bone marrow oedema scores (range 0-189). Patients were followed on arthritis development and HAQ scores were repeated when clinical arthritis had developed., Results: The median HAQ score at presentation with CSA was 0.50. Higher MRI-inflammation scores were associated with higher HAQ scores (β=0.017, 95% CI=0.004 to 0.030). During median 103 weeks follow-up, 44 patients progressed to clinical arthritis. HAQ scores ≥1.0 were associated with arthritis development (HR=2.50, 95% CI=1.03 to 6.10). Within converters, median HAQ scores did not increase from presentation with CSA to arthritis development (0.88 and 0.75, p=0.36)., Conclusions: HAQ scores ≥1.0 at presentation were associated with the development of clinical arthritis. Functional limitations in the prearthritis phase of CSA were as serious as in the early clinical phase, demonstrating the relevance of CSA from patients' perspectives., Competing Interests: Competing interests: None declared.

Objective: The objective of this study was to evaluate the reliability of recognising structural lesions on MRI (erosions, fatty lesions, ankylosis) of the sacroiliac joints (MRI-SIJ) in clinical practice compared to a central reading in patients with a possible recent axial spondyloarthritis (axSpA)., Methods: Patients aged 18-50 years, with recent (<3 years) and chronic (≥3 months) inflammatory back pain, suggestive of axSpA were included in the DEvenir des Spondyloarthrites Indifférenciées Récentes (DESIR) cohort. MRI-SIJ structural lesions were scored by non-trained local readers, and by two trained central readers. Local readers scored each SIJ as normal, doubtful or definite lesions. Central readers scored separately each type of lesion. The central reading (mean of the two central readers' scores) was the external standard. Agreement (κ) was calculated first between local (3 definitions of a positive MRI-SIJ) and central readings (9 definitions), and then between the two central readers., Results: 664/708 patients with complete available images were included. Agreements between local and central readings were overall 'fair', except when considering at least 2 or 3 fatty lesions and at least 3 erosions and/or fatty lesions where agreement was 'moderate'. Agreement between central readers was similar. MRI-SIJ was positive for 52.6% of patients according to central reading (at least 1 structural lesion) and for 35.4% of patients according to local reading (at least unilateral 'doubtful' or 'definite' structural lesions)., Conclusions: Agreement on a positive structural MRI-SIJ was fair to moderate between local and central readings, as well as between central readers. The reliability improved when fatty lesions were considered., Trial Registration Number: NCTO 164 8907., Competing Interests: Conflicts of Interest: None declared.