Clinical phenotype, MRI inflammatory involvement, and treatment patterns in HLA-B27 positive and negative axial spondyloarthritis: a Saudi MRI-based cohort study

Abstract Background HLA-B27 is strongly associated with axial spondyloarthritis (axSpA) and influences disease phenotype, though its prevalence and clinical relevance vary by population. Magnetic resonance imaging (MRI)-based cohorts offer substantial information about early axSpA detection and phenotype expression. Data from Saudi Arabia remain limited. Objective To compare clinical characteristics, diagnostic delay, inflammatory markers, MRI findings, and treatment patterns between HLA-B27-positive and HLA-B27-negative patients with MRI-confirmed axial spondyloarthritis. Methods This retrospective cross-sectional study included adults with clinician-diagnosed axSpA fulfilling ASAS imaging criteria. Clinical features, C-reactive protein (CRP) levels, MRI findings, and treatment utilization were compared between HLA-B27 groups. Diagnostic delay was analyzed as continuous and categorical data. Results Eighty-four patients were included (32 HLA-B27 positive; 52 HLA-B27 negative). HLA-B27 positive patients were more frequently male (p = 0.004) and had higher rates of uveitis (p = 0.006), family history of SpA (p < 0.001), and elevated CRP levels (p < 0.001). Diagnostic delay was prolonged in both groups. Median diagnostic delay did not differ significantly between groups (p = 0.48). Spinal inflammatory involvement on MRI was more frequent in HLA-B27 positive patients but did not reach statistical significance (p = 0.11). No significant differences in biologic treatment utilization were observed. Conclusion In this MRI-confirmed axial spondyloarthritis cohort, HLA-B27 positive patients exhibited a more defined axial and extra-musculoskeletal phenotype with higher systemic inflammation. Peripheral manifestations, diagnostic delay, and biologic treatment patterns were broadly comparable between HLA-B27 subgroups. These findings highlight regional phenotype variation and support the continued role of MRI-based evaluation in axSpA.