Ankylosing Spondylitis (Axial Spondyloarthritis)

Insidious-onset inflammatory back and buttock pain in young adults (<40y), following a chronic relapsing-remitting course. Males are affected more often than females. The term axial spondyloarthritis (axSpA) has largely replaced “ankylosing spondylitis” as the umbrella diagnosis, encompassing both radiographic (AS) and non-radiographic disease.

Clinical features

Characterised by:

• Gradual onset before age 40
• Symptom duration >3 months
• Low back and buttock pain, prolonged morning stiffness, night pain (may wake in the second half of the night)
• Improvement with exercise/activity, failure to improve with rest
• Response to NSAIDs
• Reduced lower spinal range of motion (progressive), progressive limitation of chest expansion
• Bilateral or unilateral sacroiliitis

Disease predominantly affects the sacroiliac joints initially before progressing to the lumbar, then thoracic and cervical spine. Other features:

• Enthesitis (inflammation at tendon/ligament bone attachments) is a hallmark — usually affects the heels (Achilles tendinitis, plantar fasciitis)
• Dactylitis (inflammation of a whole finger or toe)
• Peripheral arthritis — usually oligoarticular, asymmetrical, predominantly lower limb; may also affect hips, shoulders, costochondral joints
• Extra-articular features: acute anterior uveitis (sudden unilateral eye pain, photophobia, lacrimation, circumlimbal conjunctival injection — urgent ophthalmology referral for corticosteroid drops and mydriatics); less commonly aortic insufficiency (aortitis), cardiac conduction defects, apical pulmonary fibrosis

Age of onset	Adolescence to 40 years
Gender	Predominantly male
Onset	Gradual
HLA-B27 prevalence	>90%
Articular involvement	Spine 100%; peripheral joints up to 20%
Extra-articular involvement	Eyes (acute anterior uveitis) up to 30%; heart/vessels/lungs 1–4%; skin/nails <20%; GI tract — IBD in 7%, subclinical GI inflammation up to 66%; genitourinary rare

Diagnosis

• ESR/CRP, X-ray/MRI of the sacroiliac joints (diagnostic). CT/bone scan should not be used.
• HLA-B27: present in >90% of AS patients, but also ~10% of the general Australian population — not diagnostic in isolation. An HLA-B27-positive person has an ~8% lifetime risk of developing AS, rising to ~20% with an affected first-degree relative.

Poor prognostic factors: hip involvement; age <16 years at onset; and, within 2 years of symptom onset, three or more of: ESR >30mm/hr or CRP >6mg/L, limited spinal movement, dactylitis, peripheral oligoarthritis, inadequate NSAID response.

Management

Non-pharmacological

• Patient education, encouragement of long-term exercise, coping strategies for psychosocial impact (workforce participation, socialisation, sexual function, sleep) — a biopsychosocial approach is recommended.
• Regular exercise/physiotherapy — improves spinal mobility and mental health.
• Smoking cessation.

Pharmacological (BSR axial spondyloarthritis guideline, 2025)

1. NSAIDs — an adequate trial of two NSAIDs is first-line.
2. First-line b/tsDMARD (if inadequate NSAID response): a TNF inhibitor (adalimumab, etanercept, infliximab, golimumab, certolizumab pegol).
3. Second-line onwards: TNFi, an IL-17 inhibitor (secukinumab, ixekizumab, bimekizumab) or a JAK inhibitor (tofacitinib, upadacitinib) — tailored to the individual’s extra-musculoskeletal manifestations. IL-17 inhibitors can be less effective for, or worsen, coexisting Crohn’s disease/ulcerative colitis, so a TNFi or JAKi is preferred when IBD coexists; TNFi (adalimumab/infliximab/golimumab) are preferred when uveitis or psoriasis coexists.
4. Response is tracked using BASDAI (≥50% or 2-point improvement), spinal pain score (≥2-point improvement) or ASDAS (≥1.1-point improvement).
5. Sustained responders: tapering may be considered; withdrawal of the b/tsDMARD is not recommended.
6. Multiple b/tsDMARD failures: reconsider alternative diagnoses.

(registry: bsr-axial-spondyloarthritis-2025; verified 2026-07-23)

• Intra-articular/peritendinous steroid injections for sacroiliitis, peripheral arthritis or enthesitis.
• csDMARDs (sulfasalazine preferred, or methotrexate/leflunomide) may help peripheral arthritis but have no effect on axial inflammation — rarely required.
• JAK inhibitors carry the same class-wide TGA cardiovascular/malignancy/VTE boxed warning as in rheumatoid arthritis (see rheumatoid-arthritis.md) — the same pre-treatment screening and monitoring protocol applies.