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Data-driven MRI definitions for active and structural sacroiliac joint lesions in juvenile spondyloarthritis typical of axial disease; a cross-sectional international study.

OBJECTIVE
We aimed to determine quantitative sacroiliac joint (SIJ) magnetic resonance imaging cut-offs for active and structural lesions that will be incorporated as imaging domains in classification criteria of axial disease in juvenile spondyloarthritis (JSpA).


METHODS
MRI scans from an international cross-section of JSpA patients were reviewed by six musculoskeletal imaging experts blinded to clinical details. Raters globally assessed the presence/absence of lesions typical of axial SpA and performed SIJ quadrant or joint based scoring. 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 as the reference standard. Cut-offs were validated in an independent cohort.


RESULTS
Imaging from 243 subjects, 61% male, median age 14.9 years, had sequences available for detailed MRI scoring. Optimal cutoffs for defining lesions typical of axial disease in JSpA were: 1) inflammatory lesion: bone marrow edema in ≥3 SIJ quadrants across all SIJ MRI slices (sensitivity 98.6%, specificity 96.5%); 2) structural lesion(s): erosion in ≥3 quadrants or sclerosis or fat lesion in ≥2 SIJ quadrants or backfill or ankylosis in ≥2 joint halves across all SIJ MRI slices (sensitivity 98.6%, specificity 95.5%). Sensitivity and specificity of the optimal cut-offs in the validation cohort were excellent.


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 and excellent reliability. This article is protected by copyright. All rights reserved.