| Summary: | <p><strong>Objective:</strong> To describe the radiographic phenotype of axial spondyloarthritis (axSpA) according to the carriage of HLA‐B27.</p>
<p><strong>Methods:</strong> An international collaboration compared the radiographic phenotype of axSpA according to HLA‐B27 status. Patients with ankylosing spondylitis and axial psoriatic arthritis (PsA) were collected. Radiographs were read centrally, blinded to clinical details. The symmetry of the sacroiliac joints and lumbar syndesmophytes, the morphology of syndesmophytes (typical marginal vs atypical chunky) together with the modified Stoke Ankylosing spondylitis spinal score (mSASSS) and PsA spondylitis radiographic index (PASRI), were recorded.</p>
<p><strong>Results:</strong> 244 PsA patients and 198 AS patients were included. In PsA, 60 (25%) were HLA‐B27 positive while in AS, 148 (75%) were HLA‐B27 positive. Patients with HLA‐B27 were younger, more often male and had a longer duration of disease. In multivariable logistic regression HLA‐B27 was significantly associated with syndesmophyte symmetry (OR 3.02 (95% CI: 1.38‐6.61)) and marginal syndesmophytes (OR: 1.97 (95% CI 1.16‐3.36)) but not with sacroiliac symmetry. Mean radiographic scores were higher for patients with HLA‐B27.</p>
<p><strong>Conclusions:</strong> HLA‐B27 positive axSpA patients have more severe radiographic damage, more marginal syndesmophytes, and more frequent syndesmophyte symmetry compared to HLA B27 negative patients.</p>
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