POS0173 DATA-DRIVEN MRI DEFINITIONS FOR ACTIVE AND STRUCTURAL SACROILIAC JOINT LESIONS IN JUVENILE SPONDYLOARTHRITIS TYPICAL OF AXIAL DISEASE

Abstract

Background For classification in juvenile spondyloarthritis (JSpA), it is important to develop cut-offs for active and structural lesions typical of axial disease on MRI that are readily and consistently interpreted. Since the maturing sacroiliac joint (SIJ) looks different from the adult SIJ, the criteria developed for positive MRI in adults may not be applicable in JSpA. Objectives As part of a study developing classification criteria for axial disease in JSpA, we aimed to determine quantitative SIJ imaging lesion cut-offs for inflammatory and structural lesions typical of axial JSpA using majority imaging expert decision as the reference criterion. Methods Subjects were a retrospective cohort of children with SpA who met the provisional Pediatric Rheumatology International Trials Organization criteria for enthesitis/spondylitis-related juvenile idiopathic arthritis or had a rheumatologist JSpA diagnosis. All subjects had symptom onset prior to age 18 years and underwent MRI as part of a diagnostic evaluation for axial disease. To enable SIJ quadrant-based scoring, all MRIs included semi-coronal slices through the cartilaginous part of the joint on fluid sensitive sequences and on T1-weighted sequences for the assessment of inflammation and structural lesions, respectively. MRIs were reviewed by 6 musculoskeletal imaging experts who were blinded to clinical details. MRI evaluation of the SIJ was based on standardized lesion definitions that were decided by consensus of the central imaging team and represented a mix of definitions from ASAS and the Juvenile Arthritis MRI Score Outcome Measures in Rheumatology working group. Using a web-based interface, raters globally assessed the presence or absence of lesions typical of axial SpA and performed SIJ quadrant or joint based scoring. Lesion scores were generated by averaging the scores of all raters. Sensitivity and specificity of lesion cut-offs were calculated using rater majority (≥4/6 raters) on a global assessment of the presence/absence of active or structural lesions typical of axial SpA with high confidence (confidence of ±3 or stronger on confidence scale from -5, “Definitely No”, to +5, “Definitely Yes”) as the reference standard. Results Imaging from 243 subjects, 61% male, median age 14.9 years, had sequences available for detailed MRI scoring. Active inflammatory lesion typical of axial disease in JSpA was defined as bone marrow edema (BME) in at least 3 SIJ quadrants (sensitivity 98.6%, specificity 96.5%). For structural lesion typical of axial JSpA, the optimal cut-off was erosion in at least 3 quadrants or at least one of the following lesions in at least 2 SIJ quadrants: sclerosis, fat lesion, backfill, ankylosis (sensitivity 98.6%, specificity 95.5%). Conclusion We propose data-driven cut-offs for active inflammatory and structural lesions on MRI typical of axial disease in JSpA that have high specificity and sensitivity using central imaging global assessment as the reference standard.