Accuracy of Florbetapir PET Imaging in Alzheimer Disease.


The imaging modality is highly accurate, but its role in diagnosis and its social implications need consideration.

Imaging biomarkers have been studied as a means of detecting amyloid-beta () pathology in vivo. One such marker, the FDA-approved positron emission tomography (PET) amyloid imaging agent [18F]florbetapir, previously demonstrated correlation with autopsy findings of Aβ plaque in 35 people with baseline cognitive status ranging from normal to severely demented (JW Neurol Feb 22 2011). Now, the same investigators have conducted a manufacturer-sponsored follow-up study with 24 additional cases that came to autopsy, to assess the accuracy of florbetapir PET imaging.

Of the 59 patients, 46 came to autopsy within 12 months after imaging; the remainder did so within 2 years. The primary analysis compared ratings of florbetapir PET images by five physician readers with binary histopathological findings at autopsy (no or few Aβ plaques vs. moderate or frequent plaques). The majority rating by the five readers was 92% sensitive and 100% specific for imaging done within 2 years of autopsy; it was 96% sensitive and 100% specific within 1 year of autopsy. Overall, individual reader accuracy was similar to the majority-rating accuracy, and semiquantitative analyses of PET images were also highly accurate.

Comment: This study offers encouragement to physicians and families who seek a definitive diagnosis of Alzheimer disease (AD) in vivo so that they can make informed decisions about participation in clinical trials and other major life decisions such as planning for family needs. However, implications for insurability, employment, behavioral health, and quality of life need to be carefully considered before proceeding with amyloid imaging, as the results may be perceived as being similar to those of genetic testing in AD and other neurodegenerative diseases. Although florbetapir has been approved by the FDA, many questions remain regarding its role in diagnosis, interpretation of a patient’s images by an inexperienced reader, and reimbursement (or lack thereof) by insurance providers.

Source: Journal Watch Neurology

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