Sex differences in clinical and imaging characteristics of axial juvenile spondyloarthritis

Objectives The impact of biologic sex in axial juvenile spondyloarthritis (axJSpA) is unknown. We assessed whether biologic sex is associated with disease manifestations, patient-reported outcomes, or characteristic sacroiliac joint (SIJ) MRI lesions in a large cohort of youths with classified axJSpA. Methods This international multicentre cross-sectional study included youths aged <18 years with physician-diagnosed juvenile spondyloarthritis and fulfilling the classification criteria for axJSpA. Clinical and SIJ MRI data were available from the time axial disease was first diagnosed and were compared between males and females using Pearson's chi-squared and Wilcoxon rank-sum tests, as appropriate. Multivariable logistic regression evaluated the association of sex with inflammatory and structural MRI lesions typical of axial disease. Results Among the 143 patients included, 67.1% were male. Males had significantly greater HLA-B27 positivity, hip/groin stiffness and inflammatory marker elevation. There were no differences in peripheral arthritis, enthesitis or patient-reported outcomes. On SIJ MRI, males had significantly higher odds of unequivocal inflammatory lesions (OR 4.86, 95% CI 1.37-17.32), bone marrow oedema (OR 4.13, 95% CI 1.17-14.62) and pelvic enthesitis (OR 5.23, 95% CI 1.39-19.61) compared with females, but no differences in structural lesions were found. Conclusion In a large multicentre axJSpA cohort, males were significantly more likely to have clinical and MRI features of inflammatory sacroiliitis at the time axial disease was first diagnosed. Future trials in axJSpA should strongly consider stratification by sex in their design.