What is the role of Positron Emission Tomography (PET) scan in diagnosing Alzheimer's disease?

From the Guidelines

PET scans, specifically amyloid PET scans, are a valuable diagnostic tool for Alzheimer's disease, particularly in cases with unclear symptoms or early-onset disease, as they can detect abnormal protein deposits in the brain before symptoms become severe, with a sensitivity and specificity of 85% to 90% and 80% to 84%, respectively, as reported in the most recent study 1.

Key Points to Consider

• The use of amyloid PET scans is recommended in patients with persistent or progressive mild cognitive impairment (MCI), especially when the diagnosis is uncertain after a comprehensive workup, as stated in the study 1.
• Amyloid PET scans can provide valuable information that influences diagnostic confidence and management, and are more likely to be useful in cognitively impaired patients with equivocal etiological diagnosis, as noted in the study 1.
• The radiation exposure from these scans is relatively low and considered safe for most patients, with overall values for sensitivity and specificity of 85% to 90% and 80% to 84%, respectively, as reported in the study 1.

Important Considerations

• The interpretation of results in the clinical context may be difficult, as a sizeable percentage of cognitively normal older adults harbor pathologic markers of AD, and co-pathologies may influence CSF AD biomarker findings, as discussed in the study 1.
• The safety of lumbar puncture for CSF collection in the evaluation of patients suspected of having AD has been well established, but it is always important to assess safety and communicate risks and burdens appropriately, as noted in the study 1.

Recommendations

• Amyloid PET scans should be used in accordance with the appropriate use criteria, as recommended by the Amyloid Imaging Task Force, the Society of Nuclear Medicine and Molecular Imaging, and the Alzheimer’s Association, as stated in the study 1.
• Patients should be evaluated by a dementia expert, and the knowledge of the presence or absence of amyloid deposition should be felt to add to patient care, as recommended in the study 1.
• Insurance coverage varies, so patients should check with their providers before scheduling, as noted in the study 1.

From the FDA Drug Label

Amyvid is a radioactive diagnostic agent for Positron Emission Tomography (PET) imaging of the brain to estimate β-amyloid neuritic plaque density in adult patients with cognitive impairment who are being evaluated for Alzheimer's Disease (AD) and other causes of cognitive decline A negative Amyvid scan indicates sparse to no neuritic plaques, and is inconsistent with a neuropathological diagnosis of AD at the time of image acquisition; a negative scan result reduces the likelihood that a patient's cognitive impairment is due to AD A positive Amyvid scan indicates moderate to frequent amyloid neuritic plaques; neuropathological examination has shown this amount of amyloid neuritic plaque is present in patients with AD, but may also be present in patients with other types of neurologic conditions as well as older people with normal cognition.

Key Points:

• Amyvid is used for PET imaging to estimate β-amyloid neuritic plaque density in adult patients with cognitive impairment.
• A negative scan result reduces the likelihood of Alzheimer's Disease (AD).
• A positive scan result indicates moderate to frequent amyloid neuritic plaques, which may be present in AD, but also in other neurologic conditions.
• Limitations of Use: A positive Amyvid scan does not establish a diagnosis of AD or other cognitive disorder 2, 2, 2.

From the Research

Pet Scan Alzheimer’s

• Pet scans are used to detect brain Aβ deposition, one of the neuropathological hallmarks of Alzheimer's disease 3.
• Amyloid positron emission tomography (PET) imaging enables in vivo detection of brain Aβ deposition and has increasing evidence to support its clinical utility 3.
• The Amyloid Imaging Taskforce has developed appropriate use criteria to guide clinicians on when to use amyloid PET imaging 3.

Diagnostic Value of Pet Scans

• Pet scans can be used to investigate changes in cerebral glucose metabolism, various neurotransmitter systems, neuroinflammation, and the protein aggregates that are characteristic of Alzheimer's disease 4.
• Amyloid imaging could be useful as an early diagnostic marker of Alzheimer's disease and for selecting patients for anti-amyloid-beta therapy 4.
• Fdg-Pet and amyloid Pet imaging are valuable in the assessment of patients with Alzheimer's disease 5.

Clinical Application of Pet Scans

• Both amyloid and Fdg-Pet meet criteria for suitable biomarkers for the diagnosis of Alzheimer's disease 6.
• Pet scans can help in differentiating Alzheimer's disease from other causes of dementia such as frontotemporal dementia and dementia of Lewy body 5.
• Amyloid brain Pet may exclude significant amyloid deposition and thus Alzheimer's disease in appropriate clinical setting 5.

Future Directions

• Multitracer Pet studies are unlikely to be used routinely in the clinic for Alzheimer's disease, but are very informative in a research context 4.
• Future studies with standardized, uniform thresholds and a lengthier longitudinal follow-up need to be conducted to allow for surer conclusions about the future role of Pet in clinical practice 6.
• The new amyloid tracers are increasingly being included in the proposed updated diagnostic criteria, and may allow earlier diagnosis 7.