What imaging studies should be ordered to evaluate suspected psoriatic arthritis (PsA)?

Imaging Studies for Suspected Psoriatic Arthritis

For suspected psoriatic arthritis (PsA), conventional radiography should be ordered first, followed by ultrasound or MRI for peripheral manifestations, and MRI for axial involvement when radiographs are negative or equivocal. 1, 2

Initial Imaging Approach

First-line Imaging:

• Conventional radiography of affected peripheral joints and/or sacroiliac joints
  • For peripheral PsA: Radiographs of hands and feet
  • For axial symptoms: AP view of the pelvis to evaluate sacroiliac joints 1, 2

Second-line Imaging (if radiographs are negative/equivocal):

• For peripheral manifestations:
  • Ultrasound of affected joints, tendons, and entheses 1, 3
  • MRI of affected peripheral joints when ultrasound is inconclusive 4, 5
• For axial manifestations:
  • MRI of sacroiliac joints 1, 2

Specific Imaging Features by Manifestation

Peripheral Joint Involvement

• Radiography can detect:

  • Erosions at joint margins
  • Joint space narrowing
  • Periostitis
  • Pencil-in-cup deformities (in advanced disease) 6

• Ultrasound can detect early changes:

  • Synovitis (joint effusion, synovial hypertrophy)
  • Tenosynovitis
  • Enthesitis (inflammation at tendon/ligament insertions)
  • Power Doppler signal indicating active inflammation 3, 7

• MRI can detect:

  • Early inflammatory changes in joints
  • Bone marrow edema
  • Tenosynovitis
  • Dactylitis (sausage digit)
  • Enthesitis 4, 5

Axial Involvement

• Radiography of sacroiliac joints:

  • Limited sensitivity for early disease (19-72%)
  • Can detect erosions, sclerosis, and ankylosis in advanced disease 1, 2

• MRI of sacroiliac joints:

  • Can detect inflammatory changes 3-7 years before radiographic evidence
  • Shows bone marrow edema and structural changes 1, 2

Important Considerations

1. Limitations of radiography:

   • Low sensitivity for early disease detection
   • Radiographs may miss more than half of patients with structural changes 1, 2
   • Interobserver agreement for radiographic findings is only fair to moderate 2

2. Ultrasound advantages:

   • Superior to clinical examination for detecting enthesitis 7
   • Can evaluate multiple sites in a single session
   • Allows dynamic assessment of tendons and joints 3

3. MRI advantages:

   • Detects both inflammatory and structural changes
   • Can evaluate both peripheral and axial manifestations
   • Particularly useful when clinical findings and radiographs are inconclusive 5

Practical Algorithm

1. Start with radiographs of clinically affected areas

   • Hands and feet for peripheral symptoms
   • Pelvis (AP view) for back/buttock pain

2. If radiographs are negative but clinical suspicion remains high:

   • For peripheral PsA: Proceed with ultrasound of affected joints/entheses
   • For axial symptoms: Order MRI of sacroiliac joints

3. If ultrasound shows peripheral inflammation but extent is unclear:

   • Consider MRI of affected peripheral areas

4. For comprehensive evaluation in patients with both axial and peripheral symptoms:

   • Consider both sacroiliac joint and peripheral joint imaging

This approach ensures early detection of inflammatory changes while using resources appropriately based on clinical presentation and initial imaging findings.