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

Psoriatic Arthritis. Radiograph of both hands demonstrates ankylosis of numerous proximal and distal
interphalangeal joints (white arrows), flexion deformities and lack of significant osteoporosis.

• 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

Psoriatic Spondylitis. There are large, asymmetric osteophytes (white arrow). They are thicker than the syndesmophytes of ankylosing spondylitis and their asymmetric distribution should raise suspicion of psoriatic disease.

• 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