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Published on: December 5, 2015
by Women’s Brain Health Initiative:
Why does it take so long for most people to get an Alzheimer’s disease diagnosis? One of the reasons is a lack of diagnostic tests that can detect dementia in the early stages, before cognitive decline is evident. Having a way to accurately identify people who are showing early signs of the disease will also allow research into new, more effective treatments, since damage to the brain at that stage may be minimal and perhaps treatable.
Thankfully, research is starting to reveal potential early signs of the disease, an important first step in developing tests for early diagnosis or predicting risk of future dementia. Evidence is showing that some of the earliest signs of Alzheimer’s disease might appear in the eyes and nose, and work is underway examining the potential use of smell and eye assessments as predictors of future cognitive decline.
Are your eyes a window into your brain?
One of the distinguishing characteristics of Alzheimer’s disease is the accumulation of beta-amyloid plaques in the brain. Early research suggests these plaques can also build up in the eyes, possibly migrating along the optic nerve from the brain. Several studies have conducted retinal scans using different technologies and all successfully identified which participants had Alzheimer’s disease and ruling out the cognitively healthy participants.
Two examples are:
Retinal scanning shows promise as a tool for both early detection and monitoring of Alzheimer’s disease.
The eyes may hold even more promise as the window into what is going on in the brain. Research in the US and the UK is suggesting yet another way our eyes may provide early clues about future development of dementia.
A simple, painless eye-tracking test seems to provide a way to differentiate between people with early-stage memory loss and people with normal brain function.
Research done in Atlanta had volunteers watch a screen as images flashed before their eyes. Participants with memory problems showed a slight delay in their response when new images appeared. Researchers concluded that eye tracking tests may make it possible to predict whether a person is on a trajectory to develop Alzheimer’s disease or not, about three years before any symptoms appear.
Does your nose know?
One of the first parts of the brain to be affected in cognitive decline is the area responsible for your sense of smell. So, it’s not surprising that losing your sense of smell is considered a potential early sign of dementia.
Many studies have been done to explore the relationship between sense of smell and cognitive decline, trying to determine if smell assessments can be used as predictors of future neurodegenerative diseases.
An Australian study worked with a group of 308 participants, aged 46 to 86, who had no memory problems at the outset. Participants were given a sniff test, which tested their ability to distinguish between different scents.
Those who demonstrated a poor ability to distinguish different smells during the baseline test were more likely to show signs of mental decline three years later.
Another study done in New York City had over 1,000 older adults do a scratch-and-sniff test of 40 common items, asking them to identify each smell from a list of four options. The test was conducted three times between 2004 and 2010. The study revealed that those who scored poorly on the test were more likely to experience cognitive decline over time, but the researchers caution that the results don’t prove this approach could be used as a diagnostic tool to determine if someone will definitely decline over time.
In 2011, Dr. Oz, the well-known and popular TV doctor, posted a do-it-yourself “Alzheimer’s Smell Test” on his website suggesting if you can’t identify the 12 common items on his list by their smell (when tested by a friend or partner) then you should speak to your doctor. The list included fruits like lemon and cherry, flowers like rose and lilac, along with other distinctive aromas such as smoke and leather.
But in 2012, WebMD responded with an online article, No Proof Alzheimer’s Smell Test Works, warning that one must be careful when interpreting the results of DIY smell tests such as the one Dr. Oz suggested. The article indicates that performing poorly on a smell test might not be pointing to an eventual Alzheimer’s diagnosis, but might instead confirm that “you are getting older and your sense of smell is fading.” Yes, studies do seem to consistently show that loss of smell and Alzheimer’s disease often occur together, but more research is needed to prove whether smell tests can accurately predict future development of cognitive decline.
Newer research on the smell-dementia link, conducted by University of Florida Health researchers in 2013, showed that a smell test using peanut butter and a ruler could be used to confirm a diagnosis of early stage Alzheimer’s disease. This study found that early stage Alzheimer’s patients experience a dramatic difference between their left and right nostril in detecting the smell of peanut butter; their left nostril was impaired and unable to detect the smell until it was 10cm away, on average. This test requires more study and for now it is considered suitable only for confirming a diagnosis that has already been made using traditional methods; it cannot be considered an accurate method for early detection on its own.
The best way to prevent cognitive decline is to identify those who are at higher risk early. The eyes and nose certainly seem to suggest that they may be effective tools for risk assessment, early detection and monitoring of dementia. With more research, someday anyone worried they are showing early signs of dementia may be able to have their eye doctor look for any signs during a regular exam, or may be able to take a simple smell test. The simplicity and cost effectiveness of those options could dramatically increase the numbers of people getting diagnosed early.
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