A group of rheumatic diseases characterized by axial and/or peripheral arthritis and enthesitis (inflammation at the bony insertion of tendons and ligaments)

  • Enthesitis-related arthritis
  • Ankylosing spondylitis (AS)
  • Psoriatic arthritis
  • Inflammatory bowel disease–associated arthropathy
  • Reactive arthritis


  • Spondyloarthritis accounts for 15–20% of juvenile arthritis or more.
  • Nonradiographic axial spondyloarthritis (male = female)
  • AS typically affects adolescent boys (male-to-female ratio is 2 to 3:1).


Prevalence of AS mirrors that of HLA-B27 in a population

  • European descent 8% HLA-B27+ and 0.5% AS

Risk Factors


  • HLA-B27 associated
  • Risk of developing ERA with HLA-B27 is approximately 1–3%. Usually, there is a family history of a male relative with the disease.
  • HLA-B27–positive with a family history of AS have a 10-fold increased risk of AS compared to HLA-B27–positive person with no family history.


  • Inflammatory synovitis of joints and inflammation at sites of ligament and tendon attachment to bone (entheses).
  • Progression to ankylosis is a result of calcification of the anterior and posterior longitudinal ligaments of the spine.


  • Autoimmune or autoinflammatory arthritis of unknown etiology, likely multifactorial
  • Microbiome may play a role in disease.

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