Psoriatic Arthritis

Major points

• Almost always accompanies skin disease, especially nail changes
• Mostly involves DIP joints of hands > feet
• Classical deformity is called “cup-and-pencil deformity”
  • Erosion of one end of bone with expansion of the base of the contiguous metacarpal

Psoriatic Arthritis. Radiograph of both hands demonstrates cup-and-pencil deformities of
both thumbs and erosion of DIP joint of left middle finger

• There is often resorption of terminal phalanges
• There is usually no osteoporosis
  
  
• Most are HLA-B27 positive, RA factor negative
  
  
• Characteristic findings
  
  
  • Tends to involve smaller joints of hand and foot more than larger joints
  • Asymmetrical joint involvement
  • Affects both the juxta-articular and articular margins of joint
     

• As with ankylosing spondylitis and Reiter’s syndrome, bone proliferation is a major feature. Manifests itself with:
  • Bony excrescences
  • Periosteal new bone formation (common)
  • Entire phalanx may become “cloaked” in new bone
    • “Ivory phalanx”
      • Most frequent in terminal phalanges of toes, especially first
  • Ankylosis is common
    • Especially in PIP and DIP joints of hands and feet
      • Feature common to seronegative spondyloarthropathies
  • Whiskering at sites of tendinous insertion (enthesopathy) occurs
• Soft tissue swelling of an entire digit (sausage digit)
• Destruction of IP joint of great toes with exuberant callous formation is characteristic
• Resorption of tufts of terminal phalanges is characteristic
  
  
• Spine
  
  
  • Asymmetric paravertebral ossification
    • Usually thicker and larger than syndesmophytes of ankylosing spondylitis or inflammatory bowel disease
  • Occasionally, there are incomplete non-marginal syndesmophytes similar to AS

• Bilateral sacroiliitis is most common
  
  

• May produce erosions and sclerosis
• May produce widening of the SI joints
• SI joint involvement occurs in about 10-25% of patients with moderate to severe psoriasis

Resnick, 4^th Edition