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.