The Phenotype of Axial Spondyloarthritis: Is It Dependent on HLA–B27 Status?

Objective To describe the radiographic phenotype of axial spondyloarthritis (SpA) according to the presence of HLA–B27. Methods An international collaboration compared the radiographic phenotype of axial SpA according to HLA–B27 status. Patients with ankylosing spondylitis (AS) and axial psoriatic arthritis (PsA) were collected. Radiographs were read centrally, blinded to clinical details. The symmetry of the sacroiliac joints and lumbar syndesmophytes and the morphology of syndesmophytes (typical marginal versus atypical chunky), together with the modified Stoke Ankylosing Spondylitis Spine Score and the Psoriatic Arthritis Spondylitis Radiographic Index, were recorded. Results A total of 244 patients with PsA and 198 patients with AS were included. In PsA, 60 patients (25%) were HLA–B27 positive while in AS, 148 patients (75%) were HLA–B27 positive. Patients with HLA–B27 were younger and more often male and had a longer duration of disease. In multivariable logistic regression, HLA–B27 was significantly associated with syndesmophyte symmetry (odds ratio [OR] 3.02 [95% confidence interval (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. Conclusion Patients with axial SpA who are positive for HLA–B27 have more severe radiographic damage, more marginal syndesmophytes, and more frequent syndesmophyte symmetry compared to patients who are negative for HLA–B27.