How do I order a PET (Positron Emission Tomography) scan for Alzheimer's disease?

Ordering PET Scans for Alzheimer's Disease

PET amyloid imaging tests should only be ordered by dementia experts according to established appropriate use criteria, not by primary care providers. 1

When to Consider Amyloid PET Imaging

• Amyloid PET is appropriate only for patients with cognitive impairment who have:

  • Undergone baseline clinical and structural brain imaging evaluation 1
  • Been evaluated by a cognitive disorders specialist 1
  • Continued diagnostic uncertainty regarding the underlying pathological process 1

• PET amyloid imaging is most useful in:

  • Patients with early MCI or atypical clinical presentations 1
  • Cases where diagnostic confidence is intermediate 1
  • Situations requiring high confidence in the etiological diagnosis 1

Required Documentation Before Ordering Amyloid PET

A dementia expert must collect and document the following information before ordering an amyloid PET scan:

• Age and date of symptom onset 1
• Clinical syndrome identification (MCI or dementia) 1
• Evidence of persistent/progressive cognitive decline 1
• Results of structured objective mental status assessment (MMSE, MoCA) 1
• Known comorbidities 1
• Current medications and rationale for any psychoactive medications 1
• Results of neuropsychological testing 1
• Results of structural brain imaging (MRI or CT) 1
• Relevant laboratory test results (CBC, chemistry, B12, thyroid function) 1, 2
• Reasons why diagnosis remains uncertain after standard evaluation 1
• Planned treatment based on PET findings 1

Diagnostic Algorithm for Alzheimer's Disease

1. Complete baseline clinical evaluation and structural brain imaging (MRI preferred) 1, 2
2. If diagnosis remains unclear after evaluation by a dementia specialist, consider:
   • FDG PET scan first (more cost-effective) 1, 3
   • CSF analysis for Aβ42 and tau/p-tau (alternative to amyloid PET) 1
3. If diagnostic uncertainty persists after FDG PET and/or CSF analysis, then consider amyloid PET 1

Important Considerations and Limitations

• Amyloid PET is an adjunct to other diagnostic evaluations, not a standalone test 4

• A positive amyloid scan indicates moderate to frequent neuritic plaques but does not establish a diagnosis of AD 4

• A negative amyloid scan is inconsistent with AD as the cause of cognitive impairment 4

• Interpretation requires consideration of:

  • Patient's age (amyloid positivity increases with age) 1, 5
  • Clinical presentation 1
  • Possibility of multiple pathologies 1
  • ApoE4 status (if known) - carriers are more likely to be amyloid-positive 5, 6

• FDA-approved amyloid imaging agents include:

  • 18F-florbetapir (Amyvid)
  • 18F-flutemetamol
  • 18F-florbetaben 1

Common Pitfalls to Avoid

• Ordering amyloid PET without first completing a comprehensive evaluation 1
• Using amyloid PET for screening asymptomatic individuals 7
• Failing to recognize that amyloid positivity occurs in approximately 20-30% of cognitively normal older adults 5
• Interpreting a positive scan as definitive proof of Alzheimer's disease 4, 5
• Ordering amyloid PET before considering more cost-effective options like FDG PET 1