Definition and Overview
Amyloid PET is a positron emission tomography test that uses radioactive tracers to image beta-amyloid deposited in the brain in vivo. Beta-amyloid deposition is a core pathology of Alzheimer's disease, and is used as an auxiliary diagnostic tool in that the presence of this pathology can be confirmed without an autopsy.
The test is used to confirm or rule out the presence of Alzheimer's disease pathology in the process of identifying the cause of cognitive decline. However, because the presence of deposition does not mean clinical dementia, the results are interpreted in conjunction with the clinical features.
Principle
The test uses a radioactive tracer that selectively binds to beta-amyloid, such as florbetapir. When the tracer is injected intravenously, it binds to amyloid plaques deposited in the brain, and its distribution and extent are imaged using positron emission tomography.
Images are judged positive or negative based on the distribution pattern of tracers in gray matter and white matter. Positive indicates significant amyloid deposition, while negative indicates no or minimal deposition.
Indications
Amyloid PET is not a test performed on all patients with cognitive decline. It is recommended to apply selectively according to appropriate use criteria.
- If there is persistent or progressive cognitive decline of unknown cause
- When it is necessary to differentiate Alzheimer's disease from other diseases due to atypical clinical manifestations
- When it is necessary to determine the cause of early-onset (usually before age 65) dementia
In this situation, implementation is meaningful when the test results affect the direction of diagnosis and treatment. Conversely, independent testing for screening purposes in asymptomatic people is not recommended.
interpretation
Negative
A negative test indicates the absence of significant beta-amyloid deposition in the brain and is, in fact, useful in ruling out Alzheimer's pathology. If there is cognitive decline but the test is negative, causes other than Alzheimer's disease are more actively evaluated.
positivity
Positive indicates the presence of beta-amyloid deposits. However, since a positive result does not mean dementia caused by Alzheimer's disease, it is interpreted by combining cognitive symptoms, neuropsychological tests, and other test results.
Limitations and Cautions
The most important limitation is that the positivity rate increases with age even in asymptomatic normal elderly people. Because there are cases where there are no clinical symptoms even if there is deposition, there is a risk of overdiagnosis if the diagnosis is based on a positive result alone.
Therefore, amyloid PET is not a stand-alone diagnostic tool, but is positioned as an auxiliary test that is selectively applied according to appropriate use standards and interpreted in combination with clinical evaluation and other tests. Since it uses a radioactive tracer, whether to implement it or not is decided by considering the indications and benefits and burdens.