Differences in clinical features between axial psoriatic arthritis and axial spondyloarthritis: a systematic review and meta-analysis of observational studies.

INTRODUCTION

Classification of axial psoriatic arthritis (ax-PsA) within existing spondyloarthritis (SpA) criteria remains unclear. To clarify this issue, we compared the clinical features of ax-PsA and axial SpA (ax-SpA).

METHODS

In this systematic review and meta-analysis, we searched six databases (PubMed, Web of Science, Cochrane Library, Ovid, Scopus, and Embase) and one trial registry (ClinicalTrials.gov) for studies published from inception to April 20, 2025, without language restrictions. Observational studies comparing ax-PsA and ax-SpA were included. Meta-analyses were conducted to evaluate disease activity scores, spinal function scores, inflammatory markers, and HLA-B27 positivity.

RESULTS

Fifteen studies including 2,704 patients with ax-PsA and 9,248 with ax-SpA from diverse global populations were analyzed. Meta-analysis showed no significant differences between ax-PsA and ax-SpA in the Bath Ankylosing Spondylitis Disease Activity Index, Ankylosing Spondylitis Disease Activity Score, Bath Ankylosing Spondylitis Functional Index, or C-reactive protein levels. However, ax-PsA was associated with significantly lower HLA-B27 positivity compared with ax-SpA (risk ratio, 0.37; 95% confidence interval [CI], 0.32-0.43; p < 0.001). In subgroup analyses, ax-PsA demonstrated modestly better BASFI scores than ankylosing spondylitis (mean difference, -0.35; 95% CI, -0.64--0.05; p = 0.022).

CONCLUSION

The marked difference in HLA-B27 positivity between ax-PsA and ax-SpA supports their distinction as separate disease entities. Similar disease activity and functional outcomes suggest shared downstream inflammatory pathways. The lower HLA-B27 positivity in ax-PsA may reflect alternative mechanisms of interleukin (IL)-23/IL-17 axis activation, with potential therapeutic implications. Clinical differentiation should incorporate HLA-B27 testing and imaging. Future research should focus on disease course variability and subgroup-specific characteristics.

SYSTEMATIC REVIEW REGISTRATION: https://www.crd.york.ac.uk/PROSPERO/view/CRD420251043651, identifier: CRD420251043651.