Although the exact cause of Alzheimer's is unclear, scientists suspect that the formation of beta-amyloid plaques - abnormal clusters of protein fragments that accumulate between nerve cells - may play a part by triggering brain cell death, causing cognitive impairment.
Past research has suggested that in the early stages of Alzheimer's, sense of smell begins to diminish. Two new studies investigated the association further to determine whether sense of smell could be used to detect early stages of Alzheimer's.
The first study was led by Dr. Matthew E. Growdon of Harvard Medical School and Harvard School of Public Health in Boston, MA. Dr. Growdon and colleagues analyzed 215 healthy individuals who were a part of the Harvard Aging Brain Study at Massachusetts General Hospital.
Participants underwent a series of cognitive tests as well as the 40-item University of Pennsylvania Smell Identification Test (UPSIT), which measured their olfactory function - their sense of smell. In addition, the team measured the size of two brain structures among participants that are located in the temporal lobes - the entorhinal cortex and the hippocampus (a region associated with memory) - and the levels of amyloid proteins in their brains.
Odor identification tests 'could be useful for early detection of Alzheimer's'
According to the researchers, they found that participants who had a thinner entorhinal cortex and a smaller hippocampus had worse memory and smell identification than those with a larger hippocampus and a thicker entorhinal cortex.
The results of two new studies suggest that a smell test could be used for early detection of Alzheimer's.
In addition, the team reports that participants who had high levels of amyloid proteins and a thinner entorhinal cortex - which they linked to greater brain cell death - had worse olfactory function.
Although Dr. Growdon says the team's findings should be "interpreted with caution," he believes the research "suggests that there may be a role for smell identification testing in clinically normal, older individuals who are at risk for Alzheimer's disease."
Another study, led by Dr. Davangere Devanand of the Columbia University Medical Center in New York, NY, supports this theory. The research team conducted an analysis of 1,037 elderly individuals without dementia. They followed the participants over three time periods: 2004-06, 2006-08 and 2008-10.
They found that among 757 subjects, lower UPSIT scores were associated with development of dementia and Alzheimer's disease. The risk of Alzheimer's increased by 10% for each lower point scored on UPSIT. Furthermore, they found that lower baseline UPSIT scores were linked to cognitive decline in participants who did not have cognitive impairment at study baseline.
Commenting on the findings, Dr. Devanand says:
"If further large-scale studies reproduce these results, a relatively inexpensive test such as odor identification may be able to identify subjects at increased risk of dementia and Alzheimer's disease at a very early stage, and may be useful in identifying people at increased risk of cognitive decline more broadly."
Eye imaging techniques show promise for early Alzheimer's diagnosis
But it is not only olfactory tests that may be useful for the early detection of Alzheimer's, according to a further two studies presented at the conference.
Past research has indicated that among individuals with Alzheimer's, beta-amyloid plaques similar to those found in the brain can be found in the retinas - a sensory tissue that lines the inner surface of the eyes.
Fast facts about Alzheimer's disease
- More than 5 million people in the US are living with Alzheimer's disease
- The disease is the 6th leading cause of death in the US
- Around two thirds of Americans with Alzheimer's are women
- By 2050, the number of people with Alzheimer's is expected to triple to as many as 16 million.
In the first study - which provides preliminary results for 40 out of 200 participants - Shaun Frost, of the Commonwealth Scientific and Industrial Research Organization (CSIRO) in Australia, and colleagues suggest that levels of amyloid proteins in the retina could be used to determine levels of amyloid proteins in the brain, therefore providing a potential method for early Alzheimer's detection.
To reach their findings, the team gave participants a supplement containing curcumin - a compound that binds to amyloid proteins and illuminates them. This allowed the researchers to detect amyloid plaques in the eye using a method called retinal amyloid imaging (RAI). Participants then underwent PET (position emission tomography) imaging so the researchers could correlate amyloid levels in the eye with that in the brain.
From this, they have found that so far, amyloid levels detected in the eye correspond with amyloid levels in the brain. In addition, the RAI test has been able to differentiate between subjects with and without Alzheimer's with 80.6% specificity and 100% sensitivity.
Based on their findings to date, Frost and colleagues believe that retinal tests could be used to detect the early stages of Alzheimer's disease.
"If further research shows that our initial findings are correct, it could potentially be delivered as part of an individual's regular eye check-up," says Frost. "The high resolution level of our images could also allow accurate monitoring of individual retinal plaques as a possible method to follow progression and response to therapy."
In another study, Paul. D. Hartung, president and CEO of Cognoptix Inc. in Massachusetts, and colleagues analyzed 20 individuals with potential Alzheimer's alongside 20 healthy people.
Participants underwent a fluorescent ligand eye scanning (FLES) technique that can detect amyloid proteins in the lens of the eye. This involves applying an ointment to the lower eyelids, which illuminates the amyloid proteins. The proteins are then detected through laser scanning. All participants also underwent PET imaging so amyloid levels in their brains could be estimated.
According to the researchers, the eye imaging technique was able to differentiate between individuals with and without Alzheimer's with 95% specificity and 85% sensitivity, and amyloid levels in the eye significantly correlated with levels found in the brain using PET imaging.
Commenting on the team's findings, Dr. Pierre N. Tariot, director of the Banner Alzheimer's Institute in Phoenix, AZ, and principal investigator of the study, says:
"There is a critical need for a fast, dependable, low-cost and readily available test for the early diagnosis and management of Alzheimer's disease. This [eye imaging] system shows promise as a technique for early detection and monitoring of the disease."
Medical News Today recently reported on a new analysis suggesting that Alzheimer's disease can be preventable in a third of cases through making certain lifestyle changes, such as giving up smoking, increasing exercise and tackling obesity.
Written by Honor Whiteman