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Alzheimer's Disease
Alzheimer’s disease (AD), the most common and fastest growing form dementia in the aging population, accounts for more than 60 percent of all dementia-related diseases.
Irreversible and progressive, AD slowly destroys memory and thinking skills and, eventually, the ability to carry out the simplest tasks of daily living. Although treatment can help manage the symptoms of AD, there is no cure for the disease.
According to the Alzheimer’s Association, more five million people are currently living with the disorder. By 2030, that number is expected to increase to nearly eight million.
What causes AD?
AD begins deep in the brain where healthy neurons begin to work less efficiently and eventually die. This process gradually spreads to the brain’s learning and memory center—the hippocampus—and other areas of the brain, which also begin to shrink. At the same time, beta-amyloid plaques and neurofibrillary tangles begin to spread throughout the brain. Scientists believe these brain changes begin 10-20 years before the signs or symptoms of the disease appear.
New diagnostic criteria developed by the National Institute on Aging (NIA) and the Alzheimer’s Association in 2010 include three distinct stages of the disease:
- pre-clinical AD
- mild-cognitive impairment (MCI) due to AD
- final stage dementia due to AD.
The stages are characterized by specific biological states, such as decreased glucose metabolism, the accumulation of beta-amyloid plaques and brain atrophy (shrinkage). These ‘biomarkers’ can be detected and monitored by blood and cerebrospinal fluid testing and PET and MR imaging.
For more information on the new diagnostic guidelines, visit the Alzheimer’s Association website.
PET and AD
PET/CT studies are highly useful in:
- differentiating Alzheimer’s disease from other types of dementia
- evaluating ongoning cognitive decline and the effectiveness of new therapies in clinical trials
- detecting the early onset of Alzheimer’s disease.
PET scans are able to measure the brain’s rate of glucose metabolism using the tracer 18F-Fluorodeoxyglucose (FDG). In Alzheimer’s disease, characteristic brain regions–specifically areas in the temporal and parietal lobes– show decreased glucose metabolism. Researchers hope that following brain changes over time in normal elderly people, people with AD, and people with mild cognitive impairment will establish biomarker[/glossary]s of the disease. PET will play an important role in this effort, imaging the brain as the disease progresses.
PET is also emerging as a tool for identifying Alzheimer’s pathology in the pre-clinical stage.
The ability to image the build-up of beta-amyloid plaque in a living brain with PET scanning has been a major breakthrough dementia research. PET studies with a radiotracer called carbon-11-labeled Pittsburgh Compound B (C-11 PIB) has shown that adults with AD take up more PIB in the brain than do cognitively healthy older people.
While PIB continues to be used in research institutions throughout the world, other similar PET radiotracers have been approved in the US (such as AmyvidTM, VizamylTM and NeuraceqTM). These radiotracers have a longer half-life than PIB, which would facilitate PET scanning in more locations throughout the country.
These molecular imaging technologies currently used as research tools may soon help physicians to:
- routinely diagnose AD at its earliest stages, which is critical for providing the best possible care
- identify individuals who are at high risk of developing AD
- monitor the progress of the disease
- assess patient response to drug treatment
- contribute to the development of targeted drugs and therapies for dementia and AD.
A major research initiative called the National Institute on Aging’s Alzheimer’s Disease Neuroimaging Initiative (ADNI) followed hundreds of cognitively healthy individuals and others with MCI and early AD over at least five years. Participants underwent annual MRI and PET scans to allow researchers to assess changes in both the normal aging brain and in individuals with MCI and AD. By correlating the subjects’ images and other test results, such as cognitive evaluations and fluid and urine samples, researchers hope to identify valuable biomarkers of the disease process.
Additional Resources
National Plan to Address Alzheimer’s
Alzheimer’s Association TrialMatch – Clinical Trials Finder
PBS: The Forgetting: A Portrait of Alzheimer’s
NIA: Alzheimer’s Disease Fact Sheet
NIA: 2009 Progress Report on Alzheimer’s Disease: Translating New Knowledge