Scanning for Alzheimer's Disease

I recently had the opportunity observe a PET scan for Alzheimer's Disease.  This scan makes use of a recently FDA approved radioactive diagnostic agent, known as Amyvid (or Florbetapir F 18), to scan the brain for beta-amyloid plaques that are present in brains afflicted with Alzheimer's disease.  I thought that I would blog about this specific scan because it is relatively rare - although FDA approved Medicare does not cover the scan.

Beta-amyloid (Abeta) is the result of enzymes cutting amyloid precursor protein (APP.)  APP's function is not yet completely known, but it is known that APP freely passes through the fatty membrane of brain cells.  APP is typically cut into smaller segments that are designed to stay either inside or outside of brain cells.  There are many variations in the way that APP is cut, and one of the variations is Abeta.  A single Abeta molecule is relatively harmless and highly soluble, but Abeta is "sticky" and will stick to other Abeta molecules to form  oligomers.  Oligomers can exist in several different forms, however a misfolded one is believed to induce the misfolding of other oligomers.  Abeta in general is highly attracted to the synapses of brain cells, and once oligomers of Abeta progress into beta-amyloid plaque, the plaque is no longer soluble, will block synapses and eventually kill brain cells.

Amyvid was recently approved to aid in the diagnosis of Alzheimer's disease.  There are several tests that can indicate Alzheimer's disease, but none of them can fully diagnose Alzheimer's since Alzheimer's is best diagnosed postmortem.

The idea of a Florbetapir F 18 injection is that it will bind to only to beta-amyloid plaque and a PET scan can determine if the Florbetapir F 18 binded to the beta-amyloid plaque or not.  A positive scan will indicate that there are beta-amyloid plaque levels similar to those afflicted with Alzheimer's and Florbetapir F 18 binded to the beta-amyloid plaque, while a  negative scan will indicate that there is no or minimal levels of beta-amyloid plaque present in the brain and Florbetapir F 18 did not bind to the beta-amyloid plaque.

Amyvid has not been approved for the diagnosis of other cognitive disorders and alone does not diagnose Alzheimer's, although studies have shown Amyvid to have high sensitivity and specificity.

"Florbetapir gives patients with cognitive decline, their families and the physicians who treat them, more information about the amyloid plaques that may be found in their brain." - R. Edward Coleman, M.D., professor of radiology, Duke University Medical Center.