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Ankylosing Spondylitis


Definition of ankylosing spondylitis (AS)

  • An inflammatory disease of the spine affecting young (usually) HLA-B27 positive adults.
    • HLA-B27 is present in about 8% of normal population, but up to 90% of patients with ankylosing spondylitis
    • Possible environmental trigger in these patients: potentially gut micro-flora or mechanical (as yet uncertain)
  • Males are affected more than women (3:1)
  • “Rule of twos” – ank spond occurs in:
    • 2% of the general population
    • 2% of HLA-B27 positive people
    • 20% of HLA-B27 positive people with an affected family member


Presentation of ankylosing spondylitis

  • Episodic inflammation of the sacroiliac joints in late teens/early 20s
  • Morning low back pain and stiffness
    • Improves on exercise
    • May radiate into both buttocks
  • Extra-spinal features
    • Other joint pain
      • Hips (in about 1/3 of patients)
      • Shoulder girdle, costochondral joints
      • Peripheral joint involvement in about 25%, usually oligo-articular, large joint & asymmetric
    • Inflammation of the Achilles tendon insertion (enthesitis)
    • Uveitis
    • Aortitis & aortic insufficiency
    • Apical fibrosis


Mnemonic for ankylosing spondylitis

  • The six “A”s of Ank spond:
    • Atlanto-axial subluxation
    • Anterior uveitis
    • Apical fibrosis
    • Aortic regurgitation
    • Amyloidosis (renal)
    • Achilles involvement (enthesitis)



Examination of ankylosing spondylitis

  • Mobility
    • Reduced flexion in the lumbar spine
      • Modified Shober’s test: distance between the midpoint of the posterior superior iliac spines and a point 10cm vertically above when standing erect, following maximal forward flexion of the spine (normal > 15cm)
    • Increased extension at cervical spine
      • Increased occiput to wall distance: patient stands facing away from wall with heels touching wall. Occiput may not be able to touch wall in ankylosing spondylitis
    • Reduced rotation at lumber, thoracic and cervical spine
  • Other
    • Reduced chest expansion often present (restrictive pattern on lung function tests)
    • Listen for fine crepitations in upper lung zones
  • NB. The Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) is used to assess burden of active disease


Investigations in ankylosing spondylitis

  • Bloods
    • CRP and ESR usually raised
    • HLA testing is rarely indicated. Many HLA-B27 positive don’t get AS, and some people without it do.
      • Prevalence 2-8% (30% in eskimos!)
  • Imaging
    • Plain X-rays
      • Loss of definition, then sclerosis, of sacroiliac joints
        • Bilateral sacroiliac erosion on X-Ray is the most suggestive feature of AS, more than HLA-B27 positivity
      • Sclerosis of intervertebral joints and the insertions of intervertebral ligaments
      • Late changes
        • Sacroiliac joints fus
        • Intervertebral discs, facet joints and syndesmophytes all fuse
          • This is ‘bamboo spine’ or tramline appearance
    • MRI spine


Treatment of ankylosing spondylitis

  • Conservative
    • Morning exercises to preserve flexibility
  • Medical
    • NSAIDs during exacerbations
    • Local steroid injections for peripheral arthritis
    • DMARDs (e.g. methotrexate and sulphasalazine)
    • TNF-alpha blocker drugs are effective in severe disease


Prognosis of ankylosing spondylitis

  • Most patients do well with exercise and analgesia
  • 80% are employed
  • Hip disease is more disabling than other components
  • Indicators of poor prognosis:
    • High ESR
    • Poor response to NSAIDs
  • NB the rigid AS spine requires very little force to fracture – have a high index of suspicion


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