Ankylosing spondylitis

Overview

•Inflammatory back pain - insidious onset, morning stiffness >60 min, improves with exercise (not rest), night pain waking in early hours
•Peak onset age 15-35; male predominance (~3:1); HLA-B27 positive in ~90%
•Reduced lateral flexion - earliest spinal movement lost; also reduced rotation
•Classic posture - loss of lumbar lordosis, accentuated thoracic kyphosis, cervical flexion deformity ('question mark posture')
•Schober's test - mark L5 and 10 cm above; increase <5 cm on maximal forward flexion = restricted
•Anterior uveitis (iritis) - most common extra-articular feature (~40%); acute painful red eye with photophobia
•Apical pulmonary fibrosis - upper lobe fibrosis in late disease; visible on CXR
•Aortic regurgitation - from aortitis; early diastolic murmur
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Apical (upper lobe) fibrosis is the classic CXR finding in late AS - the opposite of most interstitial lung diseases (which affect lower lobes).

Investigations

🥇 First-line

•X-ray sacroiliac joints and lumbar spine - sacroiliitis (sclerosis, erosions), squaring of vertebral bodies, syndesmophytes, 'bamboo spine' in advanced disease
•ESR and CRP - raised; can be normal in up to 50%
•HLA-B27 - positive ~90%; supports diagnosis but not diagnostic alone
•Rheumatoid factor and ANA - negative (seronegative); excludes RA

🏆 Gold standard

•MRI sacroiliac joints - detects early bone marrow oedema before X-ray changes; investigation of choice if X-ray normal but clinical suspicion high

Management

Step 1 · All symptomatic patients
  1. 1Physiotherapy and regular exercise - core treatment throughout all stages
  2. 2NSAID (e.g. naproxen 500 mg twice daily) - first-line drug; review after 4 weeks; up to 70% achieve sufficient relief
Step 2 · Peripheral joint involvement only
  1. 1Sulfasalazine - only DMARD with evidence in peripheral joint disease; NOT effective for axial disease
Step 3 · Inadequate response to NSAIDs (axial disease)
  1. 1Anti-TNF agent (e.g. etanercept, adalimumab) - requires failure of 2 different NSAIDs AND active disease confirmed on 2 occasions 12 weeks apart
  2. 2Continue physiotherapy throughout
⚠️
Conventional DMARDs (methotrexate) are NOT effective for axial AS. The step from NSAIDs goes directly to anti-TNF biologics for spinal disease - never to a conventional DMARD. Sulfasalazine is only for peripheral joints.
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Anti-TNF therapy requires failure of 2 different NSAIDs (not 1, not 3) with active disease confirmed on 2 occasions 12 weeks apart.

Complications

•Spinal fusion (ankylosis) - 'bamboo spine'; progressive loss of mobility
•Atlantoaxial subluxation - cervical instability; risk of cord compression; important consideration before general anaesthesia
•Vertebral fractures - rigid fused spine + osteoporosis; risk even with minor trauma
•Apical pulmonary fibrosis - progressive respiratory impairment in late disease
•Aortic regurgitation - may progress to require valve replacement