What testing is appropriate for a Complex Regional Pain Syndrome (CRPS) patient with chronic foot pain, swelling, and inability to flex after a crush injury?

Appropriate Testing for CRPS Patient with Chronic Foot Pain, Swelling, and Limited Mobility After Crush Injury

For a CRPS patient with chronic foot pain, swelling, and inability to flex after a crush injury 10 years ago, the most appropriate initial imaging should be radiography of the foot, followed by either MRI foot without IV contrast or 3-phase bone scan if radiographs are negative or equivocal. 1

Initial Diagnostic Approach

• Plain radiographs of the foot should be the first imaging study for any chronic foot pain, including CRPS, to rule out other causes of pain such as fractures, osteoarthritis, or other osseous abnormalities 1
• Weight-bearing radiographs are recommended for optimal evaluation of foot structures 1
• Although radiographs have limited sensitivity for diagnosing CRPS specifically, they are essential to exclude other pathologies 1

Secondary Imaging for CRPS

If radiographs are negative or equivocal but clinical suspicion for CRPS remains high:

• 3-phase bone scan is highly recommended with:

  • Sensitivity of 78% and specificity of 88% according to meta-analysis 1
  • Excellent negative predictive value (88%), making it particularly useful to rule out CRPS type I 1
  • Some studies report even higher sensitivity (100%) and negative predictive value (100%) compared to MRI 1

• MRI foot without IV contrast is also appropriate with:

  • High specificity (91%) but lower sensitivity (35%) for CRPS type I 1
  • Particularly useful for CRPS type II (which occurs after nerve injury, as would be the case with a crush injury) due to its ability to visualize nerves and detect muscle denervation 1
  • Contrast-enhanced MRI may improve diagnostic accuracy in some cases 1

Imaging Selection Algorithm

1. Start with foot radiographs (weight-bearing if possible)
2. If radiographs are negative/equivocal:
   • For CRPS type I suspicion: 3-phase bone scan is preferred due to higher sensitivity
   • For CRPS type II suspicion (likely in crush injury): MRI without contrast is preferred due to ability to visualize nerve damage and muscle denervation 1
   • Consider both tests if diagnosis remains uncertain after the first test

Additional Diagnostic Considerations

• Ultrasound with power Doppler may be considered as it has shown:

  • Sensitivity of 73% and specificity of 92% for detecting increased blood flow in CRPS type I 1
  • Ability to assess nerve structures in CRPS type II 1
  • Advantage of dynamic assessment and direct clinical correlation 1

• CT is not recommended for CRPS evaluation as there is no relevant literature supporting its use 1

Clinical Diagnostic Criteria

• The Budapest Criteria should be used alongside imaging for clinical diagnosis of CRPS 2
• Assessment should include evaluation of:
  • Pain disproportionate to the inciting event
  • Evidence of autonomic dysfunction (edema, color changes)
  • Motor symptoms (weakness, decreased range of motion)
  • Trophic changes 3, 4

Important Caveats

• CRPS is primarily a clinical diagnosis; imaging studies support but do not replace clinical assessment 3, 4
• CRPS type II (causalgia) occurs after nerve injury and is the likely diagnosis in a patient with history of crush injury 1, 4
• Long-standing CRPS (10 years) may have different imaging characteristics than acute or subacute presentations 4
• Imaging findings should always be correlated with clinical presentation, as CRPS can present with various pain types (nociceptive, neuropathic, and nociplastic) that may require different treatment approaches 5