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Ankylosing Spondylitis

Krissie Lobon

Background and Classification

  • Spondyloarthritis: designates a group of diseases classified as either axial or peripheral
  • Historically associated with a family of arthridities: ankylosing spondylitis, reactive arthritis, psoriatic arthritis, peripheral arthritis, uveitis, IBD, and presence of HLA-B27 gene
  • HLA-B27 is strongly linked to disease susceptibility; however, AS can occur in absence of the gene and only ~3% of HLA-B27 positive subjects develop AS


  • Onset generally occurs in late adolescence of early adulthood
  • MSK: Inflammatory back pain (hallmark), alternating buttock pain with sacroiliac involvement, enthesitis
  • Extraarticular: Acute anterior uveitis, psoriasis, IBD
  • Typically encompasses ⅘ features: age of onset <40 years, insidious onset, improvement with exercise, no improvement with rest, pain at night (improvement upon arising)


  • Labs: No specific laboratory tests for AS
    • HLA-B27 is often present, though not necessary for diagnosis
    • Elevated CRP and ESR in 50-70% of pts with active AS and less frequently elevated in pts with non-radiographic subtype
  • Imaging
    • X-ray and MRI: joint space narrowing and sclerosis secondary to erosive changes in SI joint, pelvis, and/or spine; bony ankylosis /fusion can eventually be seen in progressive disease
    • MRI can reveal inflammatory changes; helpful in non-radiographic (X-ray negative) subtype
  • Classification criteria is used for diagnostic purposes
  • Assessment of SpondyloArthritis International Society Criteria (2011): ≥3mos back pain before 45yo and either sacroiliitis on imaging + ≥1 other axial spondyloarthritis (SpA) feature OR HLA-B27 positive + ≥2 SpA features
  • SpA features: arthritis, dactylitis, enthesitis, psoriasis, IBD, uveitis, FHx, HLA-B27


  • Initial therapy: NSAIDs for symptomatic axial spondyloarthropathies. Occasionally NSAIDs alone improve symptoms and are the only medications required
  • Refractory symptoms: TNF inhibitors followed by IL-17 inhibitors (second option, most effective in pts with concomitant psoriasis). JAK inhibitors are also improved.
  • Physical therapy: intensive rehabilitation and exercise improve mobility and symptoms