What is the role of PET scanning in the workup of Alzheimer disease (AD) in Down syndrome (DS)?

Updated: Nov 13, 2019
  • Author: Norberto Alvarez, MD; Chief Editor: Jasvinder Chawla, MD, MBA  more...
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Positron emission tomography (PET) is not considered a routine test for Alzheimer disease (AD) in individuals with Down syndrome (DS). Schapiro et al found that PET did not demonstrate any difference between healthy people with DS and individuals without mental retardation. [89]

Studies with xenon-133 inhalation technique, which evaluates cortical cerebral blood flow, showed no abnormalities in young, healthy people with DS. Significant differences were observed in individuals with DS and dementia; the greatest reduction occurred in the parietal-temporal association neocortex. [84]

In addition, errors in the interpretation of PET scans do occur, with a tendency to overdiagnose dementia. [90]

Even though there are limitations in the use of this technique, amyloid PET imaging offers a quantitative and qualitative method to measure β-amyloid deposition in the brain. Deposition of β-amyloid has been reported in studies using carbon 11-labeled Pittsburgh Compound B ([(11)C]PiB), [18F] florbetapir, and [18F] florbetaben PET imaging. [91, 92, 93, 94, 95]

These studies, in general, are in agreement that there is an increase of β-amyloid in the brain that is age correlated and preceeds the development of cognitive changes by many years. The usefulness of these studies in diagnosing AD is questionable since findings are also present in non-demented individuals. However, in the event of the development of anti-amyloid treatments these tests might prove to be useful. 

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