What are the key clinical features that differentiate axial spondyloar

Guideline-aligned answer with reasoning, red flags and references. Clinically reviewed by Dr Kola Tytler MBBS CertHE MBA MRCGP.

Key clinical features that differentiate axial spondyloarthritis from other back pain include:

Inflammatory back pain that started before the age of 45 years and lasted longer than 3 months, especially if it started before age 35, with symptoms such as waking during the second half of the night due to symptoms, buttock pain, and improvement with movement and NSAIDs .
Presence of additional features such as current or past arthritis, enthesitis, psoriasis, or a family history of spondyloarthritis or psoriasis, which increase suspicion .
Imaging evidence of sacroiliitis meeting the modified New York criteria on X-ray or MRI showing inflammation consistent with axial spondyloarthritis .
HLA‑B27 positivity, although axial spondyloarthritis can occur in HLA‑B27 negative individuals .

What are the key clinical features that differentiate axial spondyloarthritis from other forms of back pain?