Ankylosing Spondylitis

Chronic seronegative spondyloarthropathy which primarily involves the axial skeleton.


  • AS results in inflammation of the joints of the spine and is one of a group of spondyloarthropathies which includes Reactive arthritis, psoriatic arthritis, arthritis associated with inflammatory bowel disease and undifferentiated spondyloarthropathy
  • Prevalence of 0.1-2.0% of the population
  • Peak onset is in late adolescence/early adulthood (15-25)
  • More common in males (3:1)


  • HLA-B27
    • HLA-B27 allele confers around a 5-fold increase in risk- 2% of people with HLA-B27 have AS, but 92% of patients with AS have HLA-B27)
  • It is proposed that HLA-B27 heavy chains could undergo transformation such that residues of the HLA chain is occupying its own binding site
  • Another explanation is that incorrect folding of HLA-B27 molecules causes abnormal trimerisation and dimerisation.  Surface expression of these grouped molecules can initiate an immune response
  • Unlike other autoimmune conditions, inflammation in AS is partially mediated by CD8+ (cytotoxic) T cells as well as CD4+ (helper) T cells
  • The classic pathological features include subchondral granulation tissue that erodes the joint and is slowly replaced by fibrocartilage and then ossification.  This occurs at sites of attachment of ligaments/capsules to bone (enthesitis)
    • When this occurs between the discs (at the annular fibrosus insertion), you get fusion of the vertebrae via syndesmophytes and classic ‘bamboo’ spine appearance


  • Insidious onset
  • Constitutional symptoms are fairly common, particularly during flares e.g. fever, weight loss, fatigue

Back symptoms

  • Morning stiffness which will characteristically last >30 mins (not always)
  • Back pain
    • Improves with physical activity
    • Can often waken sleep/ worse at night
    • May be felt as non-specific buttock pain, particularly in early disease
      • Alternating buttock pain is classical of sacroiliitis
  • Tenderness of the spine (sacroiliac) and reduced range of movement (lumber flexion)
    • In advanced disease, there may be loss of lumbar lordosis, buttock atrophy and an exaggerated thoracic kyphosis (question mark posture)
    • Reduced Schober test (<5cm)

Other joint symptoms

  • Enthesitis of the heel (Achilles’ tendonitis and plantar fasciitis) and the tibial tuberosity
    • Can be swollen, painful- particularly in morning
  • Peripheral arthritis
    • Commonly asymmetrical and in hips, shoulder girdle, joints of the chest wall, pelvis and TMJ (cf rheumatoid)
    • Common presentation in children; also symptoms are usually milder than those of the back or than those seen in RA.

Extra-articular symptoms

  • Anterior uveitis– occurs in 20-30% of patients with ank spon.
    • NB Around a third-half of patients who develop anterior uveitis will go on the develop AS


  • There are no routine blood tests that will aid a diagnosis
    • FBC may show anaemia of chronic disease
    • Inflammatory markers may be raised and may correlate with disease activity but are non-specific
    • Rheumatoid factor may exclude rheumatoid disease (if negative), as may other antibodies
    • Genetic testing for HLA-B27 may be used (not routine)
  • Spinal imaging
    • MRI is most useful for early disease as osteophytic change may be a late feature- enthesitis/sacroiliitis will not usually be seen on an X-ray in early disease
    • X-rays may show features of sacroiliitis (blurring/fusion of the joint line)- more common in established disease
      • Can be normal early on
      • Later features include
        • Sacroiliitis (subchondral erosions/sclerosis)
        • squaring of the lumbar vertebrae
        • rarely, late/severe AS causes ‘bamboo spine’
        • syndesmophytes
  • CXR may show apical fibrosis (fibrotic lung disease is not uncommon in AS)

Diagnostic criteria (New York criteria)



  • NSAIDs or COX2 inhibitorys are the first-line drug offered to patients
    • Past evidence has suggested DMARDs (e.g. MTX/sulfasalazine) are not effective in relieving back symptoms, however, they may be helpful in patients with peripheral arthropathy.  More recent evidence is suggesting they might be beneficial in AS.
    • Other pain killers may be required
    • Corticosteroids (either oral or intraarticular injection) may be beneficial in a patient with recurrently painful arthritis affecting minimal joints
  • Biological agents (adalimumab; etanercept; infliximab- all TNF)
    • Can be used in patients with
      • confirmed (New York) Diagnosis
      • a score of >=4 on the Bath AS disease activity index
      • at least 4cm on the 0-10cm spinal pain visual analogue scale
  • Physiotherapy is VERY important as it can often prevent the fusion of the spinal joints and greatly limit morbidity
  • Surgery is a last resort to correct deformities and manage associated arthropathy
  • Lifestyle advice is important due to the complications of AS


  • Progression can lead to fixed and flexed posture (bamboo spine)
  • Cricoarytenoid arthritis may also occur, as can pleural disease, necrobiotic nodules, Caplan’s syndrome (usually associated with pneumoconiosis), fibrosing alveolitis and other idiopathic interstitial lung disease
  • Cardiovascular
    • Atherosclerosis
      • Treat cardiovascular risk factors e.g. hyperlipidaemia, hypertension etc
    • Aortic regurgitation, mitral regurgitation, AV block, fibrosis
  • Apical lung fibrosis
  • Secondary osteoarthritis/osteoporosis
  • Eye problems (recurrent/severe uveitis)
  • Amyloidosis (may cause renal dysfunction)
  • Cauda equina syndrome


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