Ankylosing Spondylitis

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  • Ankylosing spondylitis (AS) is an axial inflammatory spondyloarthropathy (axSpA) characterized by evidence of sacroiliitis on plain radiography.
  • System(s) affected: musculoskeletal; eyes; cardiac; neurologic; pulmonary
  • Synonym(s): Marie-Strümpell disease; “bamboo spine”


  • Onset usually in early 20s; rarely occurs after age 40 years
  • Male > female (approximately 2 to 3:1)

Age- and gender-adjusted rate of 6.3 to 7.3/100,000 person-years

~0.55% for AS and ~1.4% for all axSpA in the United States (1)

Etiology and Pathophysiology

  • Autoinflammation at sites of bacterial exposure (e.g., intestines) or mechanical stress in genetically susceptible individuals (2)
  • Inflammation at the insertion of tendons, ligaments, and fasciae to bone (enthesopathy) causes erosion, remodeling, and new bone formation.
  • Inflammation-independent pathways of bony changes have also been hypothesized (2).

  • 80–90% of patients with AS are HLA-B27positive.
  • Other genetic associations include endoplasmic reticulum aminopeptidase 1 (ERAP1), interleukin-23 receptor (IL23R), and gene deserts on chromosome 2p15 and 21q22 (2).

Risk Factors

  • HLA-B27
    • 1–8% of HLA-B27–positive adults have AS.
  • Positive family history
    • HLA-B27–positive child of a parent with AS has a 10–30% risk of developing the disease.

Commonly Associated Conditions

  • Peripheral arthritis (30%)
  • Enthesopathy (29%): Achilles tendonitis, plantar fasciitis
  • Uveitis (23%)
  • Psoriasis (10%)
  • Dactylitis “sausage digit” (6%)
  • Inflammatory bowel disease (IBD) (4%) (3)[A]
  • Peripheral spondyloarthritis (SpA): psoriatic arthritis, reactive arthritis, IBD-related arthritis, juvenile idiopathic arthritis
  • Aortitis and cardiac conduction defects

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