Consensus-Driven Definition for Unequivocal Sacroiliitis on Radiographs in Juvenile Spondyloarthritis

OBJECTIVE: Radiography is still used worldwide for the detection of sacroiliitis in juvenile spondyloarthritis (JSpA), despite its low sensitivity and reliability. We aimed to define unequivocal evidence of sacroiliitis on pelvic radiography in skeletally immature youth for use in classification criteria when magnetic resonance imaging (MRI) is unavailable. METHODS: Subjects were a retrospective cohort of juvenile patients with spondyloarthritis with a radiograph and MRI as part of a diagnostic evaluation for axial disease. Six musculoskeletal imaging experts underwent an iterative consensus process to define unequivocal sacroiliitis on radiography in skeletally immature youth. Radiographs were graded using the modified New York (mNY) criteria and the unequivocal sacroiliitis criteria. Interrater agreement was assessed with the Fleiss [Formula: see text] statistic. Specificity, area under the receiver operator characteristic curve (AUROC), and sensitivity of the 2 measures were tested using 2 MRI reference standards. RESULTS: A total of 112 subjects, with a median age of 14.9 (range 6.7-20.1) years, were included. The Fleiss [Formula: see text] was fair for the mNY criteria (0.54, 95% CI 0.42-0.67) and the unequivocal sacroiliitis criteria (0.58, 95% CI 0.46-0.69). The unequivocal sacroiliitis criteria achieved > 90% specificity using both MRI reference standards. Sensitivity (59.26 and 57.14 vs 44.83 and 43.33) and AUROC (0.76 and 0.76 vs 0.71 and 0.71) were higher, for both reference standards, for the unequivocal sacroiliitis in youth definition than for the mNY criteria, respectively. CONCLUSION: In this study, we propose the first consensus-derived definition to our knowledge of unequivocal sacroiliitis by radiography in skeletally immature youth. This definition achieved excellent specificity and had higher AUROC and sensitivity values than the mNY criteria using both MRI reference standards. This definition has applicability to the JSpA axial disease classification imaging criterion when MRI is unavailable.