Sacroiliitis

• Normal SI joint is uniform in size throughout

  • Only lower 2/3 of SI joint are true joint

• Earliest sign of  sacroiliitis is widening of the joint

  • Sclerosis and narrowing represent healing

• Unilateral Sacroiliitis

  • TB

• Bilateral and symmetric

  • Ankylosing spondylitis

    • Narrowing and sclerosis

    • Fusion eventually

    • Almost always bilateral

  • Inflammatory bowel disease

    • Ulcerative colitis more often then Crohn’s

      • Enteropathic arthritis more common in Crohn’s-usually knee

    • Inflammatory bowel disease usually does not affect the spine as often as ankylosing spondylitis

• Bilateral and asymmetric

  • Rheumatoid arthritis, psoriasis and Reiter’s may affect one SI joint but usually affect both

    • Usually asymmetric

  • Gout is a rare cause of sacroiliitis

    • May see erosions in spine

• SI Disease in Crohn’s

  • About 3-16% of patient with Crohn’s

  • Occurs independent of activity of bowel disease

  • HLA B27 antigen is usually elevated

  • Bilateral SI joint narrowing and erosions with sclerosis

    • Identical appearance to AS

• SI Disease in Ulcerative Colitis

  • About 1-22% of patients with UC

  • Not correlated with activity of bowel disease

  • Spondylitis usually precedes onset of bowel findings

  • Appears identical to AS

  • More common in males

  • Peripheral joint involvement in 50-70%

    • Especially shoulders and hips

  • Higher incidence of elevated HLA B27 in patients with spondylitis or iritis