Should a CT scan of the back be performed with or without contrast in a patient with new onset non-traumatic back pain and recent prostate cancer diagnosis?

CT Scan for Back Pain in a Patient with Prostate Cancer: With or Without Contrast

For a 77-year-old male with new onset non-traumatic back pain and recent prostate cancer diagnosis, CT scan of the back should be performed WITHOUT contrast initially, with consideration for MRI with and without contrast as the preferred follow-up imaging if metastatic disease is suspected.

Rationale for Initial Imaging Selection

CT Without Contrast as Initial Approach

• CT without contrast provides excellent bone detail and is appropriate for initial evaluation of possible osseous metastatic disease in a patient with prostate cancer 1
• CT can detect lytic or sclerotic lesions, bony destruction, and periosteal reaction that may indicate metastatic disease 1
• The National Comprehensive Cancer Network (NCCN) guidelines indicate that CT may be performed with or without contrast for initial staging in prostate cancer patients 1

Why Not CT With Contrast Initially

• For suspected spinal metastases from prostate cancer, contrast adds little value to the initial CT evaluation of bone involvement 1
• CT without contrast is sufficient to evaluate for bony metastatic disease, which is the most common manifestation of prostate cancer spread to the spine 2
• If epidural extension or soft tissue involvement is suspected after initial imaging, MRI without and with contrast would be the preferred next step rather than CT with contrast 1

Follow-up Imaging Considerations

When to Consider MRI

• If the initial CT shows suspicious findings or is inconclusive, MRI without and with contrast of the spine is recommended as the next step 2
• MRI is superior for evaluating:
  • Bone marrow infiltration
  • Soft tissue extension
  • Spinal cord compression (which occurs in 4-8% of men with castration-resistant prostate cancer) 2
  • Occult spinal cord compression (found in up to 30% of men with castration-resistant prostate cancer) 2

Comprehensive Evaluation

• For complete staging in this high-risk scenario (new back pain in a patient with prostate cancer), a bone scan should also be considered 1, 2
• If bone scan shows focal tracer activity in the spine, MRI should follow to evaluate for possible metastatic disease and spinal cord compression risk 2

Clinical Pitfalls to Avoid

• Delayed imaging: Waiting for symptoms of cord compression can lead to irreversible neurological damage 2
• Overreliance on PSA: PSA levels may not always correlate with metastatic burden, especially in patients on androgen deprivation therapy 2
• Misinterpretation of treated lesions: Treated bone metastases often become more densely sclerotic on CT, which can be falsely interpreted as disease progression 2

Summary of Approach

1. Begin with CT spine without contrast to evaluate for bony metastatic disease
2. If suspicious findings are present, proceed to MRI spine without and with contrast
3. Consider bone scan for comprehensive evaluation of potential widespread metastatic disease
4. Early detection and intervention can prevent neurological complications from spinal metastases

This approach balances diagnostic yield with radiation exposure and cost considerations while prioritizing the detection of potentially life-threatening or function-threatening metastatic disease.