Effect of Characteristic Inflammatory and Structural Pelvic Magnetic Resonance Imaging Lesions on Expert Assessment of Axial Juvenile Spondyloarthritis.

Objective: To evaluate the influence of pelvic magnetic resonance imaging (MRI) findings on axial disease assessment in juvenile spondyloarthritis (JSpA).

Methods: This was a cross-sectional study of patients with JSpA with suspected axial disease. Three experts reviewed each case and rated their confidence (-3 to +3) in the presence of axial disease, first with clinical data and second with clinical and MRI data. Agreement was defined as ≥ 2/3 clinical experts with a rating of ≤ -1 or ≥ 1, and high confidence agreement as ≤ -2 or ≥ 2. The association of clinical features and both global assessments was tested with modified Poisson regression models.

Results: Two hundred seventy-two of 303 cases (89.8%) achieved agreement with clinical data alone. Adding imaging data affected agreement in 38.9% (118/303) and directionality of agreement in 23.4% (71/303). Agreement was facilitated in 26/31 cases and lost in 21/272 cases. Of those 71 cases that changed directionality, 33 changed from axial disease being absent to present and 38 from present to absent. The final model had an area under the receiver-operating characteristic (AUROC) curve of 0.93 and 3 factors were independently associated with expert agreement (HLA-B27: relative risk [RR] 1.41, 95% CI 1.14-1.74; pain improvement with activity: RR 1.27, 95% CI 1.05-1.54; and bone marrow edema on MRI: RR 4.08, 95% CI 2.91-5.73).

Conclusion: The addition of imaging data affected directionality and improved high confidence agreement of expert assessment of axial disease. These results underscore the integral role of MRI in the determination of axial disease in JSpA.