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This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
The Bottom Line
- Inflammatory back pain: onset <40 years, gradual onset, improves with exercise, worse at rest/night, morning stiffness >30 min
- HLA-B27 positive in ~90% of AS patients (but ~8% of general population are HLA-B27 positive — NOT diagnostic alone)
- MRI sacroiliac joints shows bone marrow oedema (early) — X-ray shows sacroiliitis and eventually bamboo spine (late)
- First-line: regular NSAIDs (not just PRN) — most effective drug for AS symptom control
- Biologic DMARDs (anti-TNF: adalimumab, etanercept; anti-IL-17: secukinumab) if ≥2 NSAIDs fail over 4 weeks
Overview
Ankylosing spondylitis (AS) is the prototype axial spondyloarthropathy, characterised by chronic inflammation of the sacroiliac joints and spine, leading to progressive bony fusion (ankylosis). The current classification uses the term "axial spondyloarthritis" (axSpA) which encompasses non-radiographic axSpA (MRI changes only) and radiographic axSpA (ankylosing spondylitis — X-ray changes of sacroiliitis). Pathologically, enthesitis (inflammation at tendon/ligament insertions into bone) is the hallmark, leading to new bone formation and eventual syndesmophyte development and spinal fusion. Extra-articular features include anterior uveitis, inflammatory bowel disease, psoriasis, and aortic regurgitation.
Epidemiology
AS affects approximately 0.1–0.5% of the UK population. Male-to-female ratio was historically reported as 3:1 but is now recognised as closer to 2:1 (women are underdiagnosed). Mean age of onset is 20–30 years — inflammatory back pain starting after age 45 makes AS unlikely. Average diagnostic delay is 8–10 years. HLA-B27 is positive in ~90% of AS patients. Family history is a strong risk factor (prevalence of ~20% in HLA-B27-positive first-degree relatives of AS patients).
Clinical Features
Symptoms
Inflammatory back pain: onset <40 years, insidious onset, improves with exercise, does NOT improve with rest, worse at night/early morning
Morning stiffness >30 minutes (often >1 hour)
Alternating buttock pain (sacroiliac joints)
Peripheral arthritis: asymmetric, large joints, lower limbs
Enthesitis: Achilles tendinitis, plantar fasciitis, chest wall pain (costochondritis)
Anterior uveitis: painful red eye, photophobia, blurred vision — occurs in ~30%
Fatigue
Signs
Reduced spinal mobility: reduced lumbar flexion (Schober test <5 cm increase), reduced lateral flexion, reduced chest expansion (<2.5 cm)
Loss of lumbar lordosis, increased thoracic kyphosis (question mark posture in advanced disease)
Sacroiliac joint tenderness
Dactylitis (sausage digits)
Entheseal tenderness (Achilles, plantar fascia insertions)
Investigations
First-line
MRI sacroiliac jointsFirst-line imaging. Shows bone marrow oedema (STIR sequence) = active sacroiliitis. Can detect disease years before X-ray changes
HLA-B27Positive in ~90% of AS. Supports diagnosis but NOT diagnostic alone. 8% of UK population is HLA-B27 positive without disease
Inflammatory markersCRP and ESR — may be raised but can be normal in AS (normal CRP does not exclude AS)
Second-line
X-ray sacroiliac joints and lumbar spineLater in disease: sacroiliac joint erosion → sclerosis → fusion. Spine: squaring of vertebral bodies, syndesmophytes, bamboo spine (advanced)
Specialist
BASDAI/BASFI scoresBath Ankylosing Spondylitis Disease Activity Index (BASDAI) and Functional Index (BASFI) — monitor disease activity and guide treatment decisions (BASDAI ≥4 = active disease)
1
First-line: NSAIDs
- Regular NSAIDs (not just PRN): most effective symptom control for AS. Try ≥2 NSAIDs sequentially for at least 4 weeks each before considering failure
- Naproxen 500 mg BD, ibuprofen 400 mg TDS, etoricoxib 90 mg OD — choice based on patient factors
- May reduce radiographic progression if taken continuously (evidence for some NSAIDs)
- Add PPI if GI risk factors
2
Exercise and physiotherapy
- Regular exercise is critical — as important as medication. Hydrotherapy is particularly beneficial
- Spinal extension exercises, postural training, breathing exercises (chest expansion)
- Lifelong commitment to exercise programme
3
Biologic DMARDs
- If inadequate response to ≥2 NSAIDs over 4 weeks AND BASDAI ≥4
- Anti-TNF: adalimumab, certolizumab, etanercept, golimumab, infliximab
- Anti-IL-17: secukinumab, ixekizumab — alternative if anti-TNF fails or contraindicated
- JAK inhibitors (tofacitinib, upadacitinib) — newer option for axial SpA
- Conventional DMARDs (methotrexate, sulfasalazine) are NOT effective for axial disease but may help peripheral arthritis
Complications
- Spinal fusion and deformity: Progressive loss of spinal mobility, kyphotic posture — spinal fractures even from minor trauma (osteoporotic and ankylosed spine)
- Anterior uveitis: ~30% — recurrent, usually unilateral. Treat urgently to prevent visual loss
- Aortic regurgitation: Aortitis in ~5% — check for early diastolic murmur
- Apical pulmonary fibrosis: Rare late complication — upper zone fibrosis
- Cauda equina syndrome: Rare — from arachnoiditis
- Osteoporosis: Despite new bone formation at entheses, generalised osteoporosis occurs — fracture risk
- Cardiovascular disease: Increased CV risk from chronic inflammation
UKMLA Exam Tips
- 1Inflammatory back pain: onset <40, gradual, improves with exercise, worse at rest/night, morning stiffness >30 min
- 2Mechanical back pain: any age, sudden onset, worse with activity, better with rest — contrasting pattern
- 3HLA-B27 is positive in 90% of AS but 8% of the general population — it is NOT diagnostic
- 4Schober test: reduced lumbar flexion (<5 cm increase on forward flexion) — classic exam test
- 5NSAIDs are first-line — NOT just for symptom relief but taken regularly as disease-modifying
- 6Conventional DMARDs (methotrexate, sulfasalazine) do NOT work for axial disease
- 7Bamboo spine on X-ray is LATE disease — early diagnosis uses MRI sacroiliac joints
practicetest your knowledge on ankylosing spondylitisApply what you've learnt with UKMLA-style questions from the iatroX Q-Bank — musculoskeletal and beyond.
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