What clinical features should I assess to differentiate ankylosing spondylitis from other causes of back pain?

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

Posted: 16 August 2025Updated: 16 August 2025 Guideline-Aligned (High Confidence) Clinically Reviewed

Dr Kola Tytler MBBS CertHE MBA MRCGPClinical Lead • iatroX

Assess for inflammatory back pain features, such as:

Waking during the second half of the night due to symptoms (recommendation 1.1.5)
Buttock pain (recommendation 1.1.5)
Improvement with movement (recommendation 1.1.5)
Improvement within 48 hours of taking NSAIDs (recommendation 1.1.5)

Additional features include:

Onset of back pain before the age of 45 years, especially before 35 years (recommendation 1.1.5)
Presence of current or past arthritis, enthesitis, or psoriasis (recommendation 1.1.5)
Family history of spondyloarthritis or psoriasis (recommendation 1.1.5)

Signs suggestive of axial spondyloarthritis:

Back pain starting before age 35 (recommendation 1.1.5)
Symptoms that wake the patient during the night (recommendation 1.1.5)
Buttock pain (recommendation 1.1.5)

Additional clinical features that may help differentiate include:

Presence of dactylitis (recommendation 1.1.9)
Enthesitis, especially if persistent, in multiple sites, or associated with other features such as uveitis or psoriasis (recommendation 1.1.10)

Key References