Can I Be Tested for Alzheimer Disease?

Dr. Sharon Orrange
Dr. Orrange is an Associate Professor of Clinical Medicine in the Division of Geriatric, Hospitalist and General Internal Medicine at the Keck School of Medicine of USC.
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Studies show that Alzheimer Disease is feared more than any other medical condition in people over 55, even cancer. It’s normal to be concerned if you find your memory is not as good as it used to be as you get older.
You may wonder: is this normal memory loss or do you have Alzheimer Disease (AD)? Are there any tests that can help you find out? There are a few ways to narrow it down.
Neuropsychological testing.
If you or a family member is worried about memory loss, a referral for neuropsychological testing is the place to start. A neuropsychologist will ask questions and have you perform simple tasks. The evaluation takes several hours. Given the lack of a reliable blood test or imaging that can distinguish AD from normal aging or other forms of dementia, this is the best we’ve got. Studies show that memory deficits associated with Alzheimer’s disease (AD) are distinct from age-related memory loss. Neuropsychological testing will help you figure this out.
Genetic testing and blood tests.
Despite easy access online to genetic testing for AD, a genetic basis is rare and really only associated with the early-onset form (symptoms before age 65), which accounts for less than one percent of cases. As of now, there are three genes that have been identified as causes of early-onset Alzheimer disease: amyloid precursor protein (APP), presenilin 1 (PSEN1), and presenilin 2 (PSEN2).
For late-onset AD, which accounts for the lion’s share of AD, the most firmly established genetic risk factor is apoprotein E ε4 (APOE ε4). In other words, late-onset AD is more complex with many factors likely playing a role,including genetics and environment. Because of this, APOE genotyping in people without any memory impairment is generally discouraged.
Imaging studies of the brain.
What about brain MRI or CT scan to see if I have AD? While it is true that a brain MRI in patients with AD shows decreased activity in certain areas of the brain (the temporal, parietal and prefrontal cortices), imaging studies alone are never enough to make a diagnosis. In someone with dementia, brain imaging can help detect treatable causes of dementia and differentiate among the subtypes. But as you know, AD is not a treatable cause of dementia—and honestly most aren’t.  
What’s new in imaging for AD patients?
PET and SPECT imaging of the brain are common imaging techniques used in AD patients. PET and SPECT work when a tracer is injected (something that will latch onto amyloid) allowing us to image areas of amyloid in the brain. Why amyloid? Misfolded proteins result in plaques of amyloid and tau proteins in the brain, leading to AD.
The use of amyloid PET imaging is a huge area of interest in Alzheimer Disease patients. The downside of amyloid PET is that amyloid can be demonstrated in the brains of adults with normal cognition as well as those with AD. Ten percent of 50 year olds with normal cognition and up to 44% of 90 year olds will have a positive amyloid PET scan.  Also, a negative amyloid PET scan in a normal person does not mean that individual cannot develop AD in the future, while a negative scan in a person with dementia reflects a high likelihood that AD is not the cause. Because of this, amyloid PET is certainly not recommended as a screening test for AD.
Dr O.

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