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Ankylosing spondylitis

Ankylosing spondylitis is a chronic seronegative spondyloarthropathy which primarily involves the axial skeleton.

Risk factors

  • HLA-B27 (positive in 90-95%)
  • Age: peak onset 15-25 years
  • Male gender
  • Family history

Clinical features


  • Low back pain
    • Progressive
    • Relieved by exercise
    • Night pain
    • Radiates to sacroiliac joints and hips
  • Morning stiffness 
  • Systemic features: fever, weight loss, fatigue


  • Question mark posture (loss of lumbar lordosis and thoracic kyphosis)
  • Sacroiliac joint tenderness (sacroiliitis)
  • Schober’s test: mark midline 10cm above the dimples of Venus and 5cm below while standing, then re-measure distance in flexion (<5cm difference implies lumbar flexion limitation that may be due to ankylosing spondylitis)
  • <5cm chest circumference expansion on inspiration 

Extra-articular features

  • Extra-articular features: A
  • Anterior uveitis
  • Aortitis
  • Aortic regurgitation
  • AV node block
  • Apical pulmonary fibrosis
  • Amyloidosis → glomerulonephritis
  • Achilles tendon (and other tendon) enthesitis


  • Clinical diagnosis
  • X-Rays: pelvis and spine (‘bamboo spine’ is a characteristic sign caused by vertebral body fusion by marginal syndesmophytes)
  • MRI: more sensitive than X-Ray
  • Bloods: FBC (anaemia), ESR (raised), CRP (raised), HLA B27 (+ve)


  • Exercise and physiotherapy: essential
  • NSAIDs (e.g. ibuprofen, naproxen, diclofenac): may need to try two or more
  • TNF-α inhibitors (e.g. etanercept) may be used when two or more NSAIDs have failed
  • Interleukin-17A inhibitors (e.g. secukinumab): may be used in place of TNF-α inhibitors

Other therapies: corticosteroid joint injections, short courses of corticosteroids, intravenous bisphosphonates