Progression of sacroiliac joint structural lesions in axial spondyloarthritis: a longitudinal comparative study of MRI and radiography among European patients in routine clinical care

Abstract Background To compare the performances of magnetic resonance imaging (MRI) and radiography in detecting changes in structural lesions of the sacroiliac joints (SIJs) in routine care patients with axial spondyloarthritis (axSpA). Methods SIJ MRIs and radiographs of routine care patients with axSpA in four European countries were collected as part of the EuroSpA Imaging Project. Patients were included if both MRIs and radiographs (≤ 6 months apart) were available at two time points (≥ 1 year apart). Images were evaluated centrally and independently by two trained readers (blinded to chronology and other imaging), applying the Spondyloarthritis Research Consortium of Canada SIJ scores (MRI) and the modified New York criteria (mNY, radiography). Intermodality agreement was assessed cross-sectionally and for change. Results One-hundred-and-five patients (65 male, mean (SD) age 38.1 (10.9) years, symptom duration 9.1 (9.7) years), with a follow-up interval of 2.6 (1.4) years) were included. Baseline agreement between radiography and MRI was slight-to-fair for erosion detection (kappa = 0.12 to 0.42), poor to slight for sclerosis (− 0.04 to 0.07), and substantial to almost perfect for ankylosis (0.66–0.86). Agreement for change over time was poor-to-slight (− 0.04 to 0.20). While lesions remained largely stable on radiography (≤ 6 patients showing change in scores, per lesion type), MRI detected change in at least one lesion in ≥ 50% of patients (positive/negative change in scores (“progression”/”regression”): sclerosis 27/30, erosion 51/38, ankylosis 14/5). A composite MRI score of damage correlated well with mNY grades (Spearman rho = 0.65–0.69). Conclusions Compared to radiography, MRI detected more SIJ structural lesion changes over time, reflecting its ability to capture dynamic changes not readily visible on radiography.