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ankylosing spondylitis (AS)


  • one of the seronegative spondyloarthropathies with a strong genetic predisposition which appears to relate to the ARTS1 and IL23R genes in addition to HLA-B27
  • men are affected more than women by a ratio of about 3:1, and the disease is generally more severe in males
  • ~90% of AS patients express the HLA-B27 genotype BUT only 5% of individuals with the HLA-B27 genotype contract the disease
  • it mainly affects joints in the spine and the sacroiliac joint in the pelvis, and can cause eventual fusion of the spine.
  • onset of symptoms is usually before age 45yrs with average age of onset being 23yrs, but given the non-specific nature of early symptoms diagnosis is usually not made until ~10 years later.
  • in the 1st 10 yrs of the disease, it is cervical dominant in 5%, lumbar dominant in ~20% and equi-dominant or minimal in each area in 75%, while 80% have symmetric sacro-iliitis 1)

clinical features

  • initial symptoms are chronic back pain and stiffness in the thoracic spine, often with pain referred to a buttock or back of thigh from sacro-iliac joint involvement
  • pain usually worst at rest improving with activity
  • adolescent onset may cause pain and swelling of large limb joints, particularly the knee
  • in prepubescent cases, the ankles and feet may be involved, where calcaneal spurs may also develop.
  • 40% develop iritis and uveitis, causing redness, eye pain, vision loss, floaters and photophobia
  • 5-10% also have or develop inflammatory bowel disease (IBD)


  • there is no specific test
  • Dx is usually made on clinical features, and MRI and XRay of the spine although plain XRay features are usually not present until 10yrs after onset
  • Schober's test is a useful clinical measure of flexion of the lumbar spine performed during examination
  • ESR and CRP may be raised during acute inflammatory periods
  • a minority are ANCA +ve
as.txt · Last modified: 2019/04/06 13:52 by

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