Ankylosing Spondylitis

 

• Chronic inflammatory disease of unknown etiology primarily affecting spine
• Most common spondyloarthropathy
  • Age-young adults
    • 15-35 years
  • Mostly male
    • M:F = 4:1
  • Mostly Caucasian
    • Caucasians to Blacks = 3:1
• Clinical findings
  • Insidious onset of low back pain and stiffness
  • Poor chest expansion
  • Stiffness
  • Exaggerated dorsal kyphosis
  • HLA-B 27 positive in >90%
• Location
  • Axial skeleton and large, usually central, appendicular joints
• Sacroiliac joint involvement
  • Hallmark of disease
  • Only synovial portion of SI joint is involved
    • Inferior and anterior portion of joint
      • Other enthesopathies like DISH can cause bridging of upper, non-synovial part of joint
  • Usually site of initial involvement
  • Bilaterally symmetric
  • Widened with erosions at first
  • Then ankylosis
• Spine
  • Usually begins at either thoracolumbar or lumbosacral junctions
    • Extends symmetrically without skip areas
      • Reiter’s and psoriasis characteristically are asymmetric and have skip areas
  • Marginal syndesmophyte formation = thin vertical dense spicules bridging the vertebral bodies
    • Ossification of outer fibers of annulus fibrosus
      • Not anterior longitudinal ligament
  • Trolley-track sign on AP view = central line of ossification (supraspinous and interspinous ligaments) with two lateral lines of ossification (apophyseal joints)
  • Bamboo spine on AP view = undulating contour due to syndesmophytes
  • Prone to fracture resulting in pseudarthrosis
  • Straightening / squaring of anterior vertebral margins
    • Osteitis of anterior corners
  • Reactive sclerosis of corners of vertebral bodies = shiny-corner sign
  • Symmetric erosions of laminar and spinous process at level of lumbar spine
  • Apophyseal  and costovertebral ankylosis
  • Periosteal whiskering
    • Sites of tendinous insertion
      • Ischial tuberosity
      • Iliac crest
      • Ischiopubic rami
      • Greater femoral trochanter
      • External occipital protuberance
      • Calcaneus
      • Patella
  • Dorsal arachnoid diverticula in lumbar spine with erosion of posterior elements
  • Atlantoaxial subluxation

Ankylosing spondylitis-Note fusion of both SI joints and thin, symmetrical
syndesmophytes bridging the intervertebral disc spaces

• Peripheral joint involvement
  • Hip is most frequently involved
  • Concentric joint narrowing
  • Few erosions
  • Protrusio acetabuli
• Temporomandibular joint
  • Joint space narrowing
  • Erosions
  • Osteophytosis
• Hand (30%)
  • Target area
    • MCP, PIP, DIP
  • Exuberant osseous proliferation
  • Osteoporosis
  • Joint space narrowing
  • Osseous erosions (deformities less striking than in rheumatoid arthritis)
• Chest
  • Bilateral upper lobe pulmonary fibrosis (1%) with upward retraction of hila
  • Resembles tuberculosis
• Cardiovascular
  • Aortitis (5%) of ascending aorta ± aortic valve insufficiency
    • Prognosis: 20% progress to significant disability
    • Occasionally death from cervical spine fracture / aortitis
• DDx
  • Reiter syndrome (unilateral asymmetric SI joint involvement, paravertebral ossifications)
  • Psoriatic arthritis (unilateral asymmetric SI joint involvement, paravertebral ossifications)
  • Inflammatory bowel disease
• Associated with:
  • Ulcerative colitis
  • Regional enteritis
    • Clinically the SI joint involvement is identical to
      • Inflammatory Bowel Disease (IBD)
  • Iritis in 25%
  • Aortic insufficiency and atrioventricular conduction defect
     

The Requisites
Dahnert 4^th Edition