What Constitutes an MRI Indicative of Axial Spondyloarthritis? A Systematic Literature Review by the Spondyloarthritis Research and Treatment Network and the Society of Skeletal Radiologists

Objectives MRI indicative of axSpA in the sacroiliac joints (SIJ) is the highest ranked variable in the 2025 ASAS-SPARTAN Revised Classification Criteria for AxSpA[1] and requires consideration of both inflammatory and structural lesions. But it lacks guidance as to the type of lesion, its location and extent. We aimed to conduct a systematic literature review (SLR) to form the evidence base for a guidance document that defines what constitutes a positive MRI indicative of axSpA. Methods The primary question for the SLR was “Which MRI lesion, or combination of lesions, in the SIJ is most sensitive and specific for an MRI considered indicative of axSpA in the SIJ?.” Three additional questions addressed an endpoint of clinician diagnosis of axSpA and the extent and location of the lesion(s). The SLR included all studies from January 2017 to July 27, 2025, that included patients with clinically suspected axial SpA undergoing MRI. Studies from a previously published SLR up to January 2017 were also included. Each study selected for data extraction was assessed independently for risk of bias (RoB) by 3 reviewers using the Quality Assessment of Diagnostic Accuracy Studies-2 tool. Results Searches in Ovid MEDLINE, Ovid Embase, Scopus, Web of Science Core Collection, and the Cochrane Library gave 1871 unique results for screening in the Covidence tool, of which 35 were selected for data extraction, and 7 were excluded. Only 2 reports described ‘MRI global indicative of axSpA’ as reference criterion for the assessment of MRI lesion definitions and only 5 reports described assessment of MRI lesion definitions in an inception cohort study design. The quantitative component for BME of the ASAS 2009/2016 definitions of a positive MRI lacked specificity. Bone marrow edema (BME) in <4 SIJ quadrants was seen in anterior SIJ slices of antepartum and postpartum women, health individuals, and athletes but in ≥4 SIJ quadrants was specific for axSpA. Erosion and fat lesion were uncommon (<5%) in health individuals and disorders that mimic axSpA (DISH). Erosion in ≥3 SIJ quadrants and fat lesion in ≥5 SIJ quadrants had high specificity for axSpA and was rarely seen in conditions that mimic axSpA. BME adjacent to erosion and/or fat lesion was highly specific for axSpA. Conclusion These results reinforce the need to revise previously reported definitions of a positive MRI for axSpA toward more stringent MRI cut-offs that detail the extent and location of MRI lesions. References [1.] Maksymowych W. [Abstract]. Arthritis Rheumatol 2025;77 Suppl 9. https://acrabstracts.org/abstract/the-assessments-in-spondyloarthritis-international-society-asas-and-spondyloarthritis-research-and-treatment-network-spartan-revised-classification-criteria-for-axial-spondyloarthritis-developmen/