Clinical Utility of Repeat Sacroiliac Joint MRI in Patients Evaluated for Axial Spondyloarthritis: A Real-World Cohort Study.

Objectives: To evaluate the real-world diagnostic and therapeutic impact of repeat sacroiliac joint magnetic resonance imaging (SIJ MRI) in patients undergoing assessment for axial spondyloarthritis (axSpA). Methods: This retrospective study included patients who underwent at least two SIJ MRI examinations from January 2010 to January 2026 at a single tertiary center. Demographic, clinical, laboratory, and imaging data were extracted from electronic medical records. MRI findings were classified according to Assessment of SpondyloArthritis International Society (ASAS) definitions. Changes between MRI1 and MRI2, diagnostic reassessment, treatment modification, and factors associated with diagnostic change were analyzed. Results: A total of 229 patients were included. The median interval between MRI examinations was 34 months. Among patients with initially negative or suspicious MRI findings, 13.0% converted to MRI-positive status on MRI2, whereas 44.8% of those with positive MRI1 findings regressed to negative or suspicious categories. Bone marrow edema (BME) was less frequent on MRI2 than MRI1 (38.0% vs. 50.2%, p = 0.003), while fat metaplasia (9.6% vs. 3.1%, p < 0.001) and sclerosis (34.9% vs. 26.6%, p = 0.006) were more common. Repeat MRI was associated with diagnostic reassessment in 41 patients (17.9%) and treatment modification in 27 patients (11.8%). In multivariate analysis, MRI1 BME positivity (OR 3.13, 95% CI 1.47-6.63, p = 0.003) and higher CRP levels (OR 1.06, 95% CI 1.01-1.11, p = 0.017) were independently associated with diagnostic reassessment. Conclusions: In routine clinical practice, repeat SIJ MRI was associated with diagnostic reassessment and treatment modification in a subset of patients undergoing evaluation for axSpA. Diagnostic reassessment was more frequently observed in patients with baseline inflammatory MRI findings and elevated inflammatory markers.