The Whitworths of Arizona, bringing science to you in everyday language.

Friday, June 10, 2011

Thoughts about PiB, a PET scan compound

We attended the Arizona Alzheimer’s Consortium Scientific Conference today. Our keynote speaker was Dr. W. E. Klunk, the inventor of PiB, a compound used with PET scans to identify Alzheimer’s plaques. Most of the information was way over our heads but we did come away with some thoughts:

1. When Dr. Klunk talked about comparing the results of PiB scans with later autopsy results, we learned that if PiB finds plaques, there’s a 97% chance of AD* on autopsy. Since Lewy bodies do not show up on a PiB scan, one would hope that it could be used to differentiate AD and LBD. You know, if the scan shows plaques, the dementia is AD and if it doesn’t show plaques, the dementia is likely LBD. Not so, because 24% of the time, a PiB scan doesn’t find plaques that do show up later on autopsy.

2. And here are some more statistics. According to Dr. Klunk, autopsies show that 40% of AD patients also have Lewy bodies—and that 80% of DLB* patients will have AD. (We also learned that is unusual for a patient with PDD* to have AD pathology—but this is another, if equally interesting issue, to be discussed in a later entry.) Therefore, even if the PiB worked perfectly, i.e., identified all patients with AD, there would still be many patients with accompanying, but unidentified, LBD.

For LBDers, these figures are sad. It means that because AD is known so well, many physicians will stop at diagnosing the AD and the accompanying LBD may never be diagnosed. Or it is diagnosed only after a serious reaction to some medication that would never have been given to someone with known LBD.

* Acronyms:

AD: Alzheimer's disease

DLB: Dementia with Lewy bodies (the LBD where demenia appears first)

PDD: Parkinson's with dementia (where Parkinson's appears first)

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