Ankylosing spondylitis is a HLA-B27 associated spondyloarthropathy. It typically presents in males (sex ratio 3:1) aged 20-30 years old.


  • Incidence: 8.00 cases per 100,000 person-years
  • Peak incidence: 20-30 years
  • Sex ratio: more common in males 3:1
Condition Relative
Lower back pain (non-specific, without sciatica)375.00
Ankylosing spondylitis1
<1 1-5 6+ 16+ 30+ 40+ 50+ 60+ 70+ 80+

Clinical features

  • typically a young man who presents with lower back pain and stiffness of insidious onset
  • stiffness is usually worse in the morning and improves with exercise
  • the patient may experience pain at night which improves on getting up

Clinical examination
  • reduced lateral flexion
  • reduced forward flexion - Schober's test - a line is drawn 10 cm above and 5 cm below the back dimples (dimples of Venus). The distance between the two lines should increase by more than 5 cm when the patient bends as far forward as possible
  • reduced chest expansion

Other features - the 'A's
  • Apical fibrosis
  • Anterior uveitis
  • Aortic regurgitation
  • Achilles tendonitis
  • AV node block
  • Amyloidosis
  • and cauda equina syndrome
  • peripheral arthritis (25%, more common if female)

Referral criteria

NICE advise:
  • all patients with suspected ankylosing spondylitis should be referred to a specialist
  • 'Do not rule out the possibility that a person has spondyloarthritis solely on the presence or absence of any individual sign, symptom or test result.'


Inflammatory markers (ESR, CRP) are typically raised although normal levels do not exclude ankylosing spondylitis.

HLA-B27 is of little use in making the diagnosis as it is positive in:
  • 90% of patients with ankylosing spondylitis
  • 10% of normal patients

Plain x-ray of the sacroiliac joints is the most useful investigation in establishing the diagnosis. Radiographs may be normal early in disease, later changes include:
  • sacroiliitis: subchondral erosions, sclerosis
  • squaring of lumbar vertebrae
  • 'bamboo spine' (late & uncommon)
  • syndesmophytes: due to ossification of outer fibers of annulus fibrosus
  • chest x-ray: apical fibrosis

If the x-ray is negative for sacroiliac joint involvement in ankylosing spondylitis but suspicion for AS remains high, the next step in the evaluation should be obtaining an MRI. Signs of early inflammation involving sacroiliac joints (bone marrow oedema) confirm the diagnosis of AS and prompt further treatment.

Spirometry may show a restrictive defect due to a combination of pulmonary fibrosis, kyphosis and ankylosis of the costovertebral joints.

Image gallery


The following is partly based on the 2010 EULAR guidelines (please see the link for more details):
  • encourage regular exercise such as swimming
  • NSAIDs are the first-line treatment
  • physiotherapy
  • the disease-modifying drugs which are used to treat rheumatoid arthritis (such as sulphasalazine) are only really useful if there is peripheral joint involvement
  • the 2010 EULAR guidelines suggest: 'Anti-TNF therapy should be given to patients with persistently high disease activity despite conventional treatments'
  • research is ongoing to see whether anti-TNF therapies such as etanercept and adalimumab should be used earlier in the course of the disease