March 3, 2017
An Alzheimer’s test that gauges a person’s ability to detect and recall specific odors may soon be available in doctor’s offices, two new studies suggest. A low cost “sniff” test could make Alzheimer’s easier to diagnose at its earliest stages, when treatments may be most effective.
Alzheimer’s affects parts of the brain critical for recognizing odors, and the ability to detect specific odors may precede memory loss and other symptoms of the disease. A number of scent tests have been developed to test odor perception as a way to diagnose early Alzheimer’s.
“There is increasing evidence that Alzheimer’s disease starts at least 10 years before the onset of memory symptoms,” said Dr. Mark Albers, the principal investigator of one of the studies, from Massachusetts General Hospital in Boston. “The development of an affordable, accessible and noninvasive means to identify healthy individuals who are at risk is a critical step to developing therapies that slow down or halt Alzheimer’s disease progression.”
In the study, published in the Annals of Neurology, the Boston researchers tested 183 visitors to the hospital’s memory clinic on their ability to identify and compare various scents. Ten of them had been diagnosed with Alzheimer’s, and 29 with mild cognitive impairment, a symptomatic stage that often precedes the disease. The remainder either had no memory problems or had general complaints about their memories.
In one part of the testing, study participants were exposed for two seconds each to 10 different smells: menthol, clove, leather, strawberry, lilac, pineapple, smoke, soap, grape or lemon. After each, they were asked to choose from a list of four scents for the one that best describes the odor.
In another part of the testing, they were exposed to 10 additional odors: banana, garlic, cherry, baby powder, grass, fruit punch, peach, chocolate, dirt and orange. They were asked to identify each, and also if the smell had been included in the earlier test. Participants were also presented with two consecutive odors and asked whether they were different or the same.
Through these and other scent tests, the researchers were able to identify correctly which of the participants had been given a diagnosis of Alzheimer’s or mild cognitive impairment, and which had memories in the normal range.
The researchers plan additional results to confirm the findings. “It is well recognized that early diagnosis and intervention are likely to produce the most effective therapeutic strategy for Alzheimer’s disease — preventing the onset or the progression of symptoms,” Dr. Albers said. “If these results hold up, this sort of inexpensive, noninvasive screening could help us identify the best candidates for novel therapies to prevent the development of symptoms of this tragic disease.”
The second study came from the Perelman School of Medicine at the University of Pennsylvania, which has developed a commonly used sniff test for Alzheimer’s. For the study, in the Journal of Alzheimer’s Disease, researchers gave 728 older men and women the Sniffin’ Sticks Odor Identification Test, which requires people to identify 16 different smells. The participants also underwent a comprehensive assessment of memory and thinking skills.
All the study participants had been previously undergone extensive evaluations by Alzheimer’s doctors at the medical center and grouped into diagnostic categories: “healthy older adult,” “mild cognitive impairment” or “Alzheimer’s.”
Combined, the sniff test and the memory and thinking exam were very accurate in predicting who likely had Alzheimer’s, who had mild cognitive impairment and who was cognitively healthy. For example, the memory test correctly identified 75 percent of those with mild cognitive impairment. But that figure rose to 87 percent when the results of the sniff test were added.
“There’s the exciting possibility here that a decline in the sense of smell can be used to identify people at risk years before they develop dementia,” said the study’s principal investigator, David R. Roalf, an assistant professor in Penn’s department of psychiatry. “These results suggest that a simple odor identification test can be a useful supplementary tool for clinically categorizing mild cognitive impairment and Alzheimer’s, and even for identifying people who are at the highest risk of worsening.”
Some Alzheimer’s clinics are already employing sniff tests to assess people for Alzheimer’s disease. They typically take 5 to 10 minutes or longer to administer, though researchers are developing shorter tests that may take only 3 minutes or so that would be easier to give. As studies show they may be effective in helping to diagnose serious memory problems, they may be used more widely in the coming years, the researchers say.
It’s important to note that a poor sense of smell does not mean you will get Alzheimer’s. An impaired sense of smell can be caused by many conditions other than Alzheimer’s, including normal aging, medications, viral illnesses, head injuries or nasal conditions. In addition, many people with Alzheimer’s retain their sense of smell, so a sniff test is by no means foolproof.
But earlier detection of Alzheimer’s may allow for treatments that may be more effective in curbing the progression of the disease. An inexpensive sniff test might also prove to be useful as a preliminary test for identifying patients who might need more extensive testing with brain scans, the researchers say.
By ALZinfo.org, The Alzheimer’s Information Site. Reviewed by Marc Flajolet, Ph.D., Fisher Center for Alzheimer’s Research Foundation at The Rockefeller University.
Dhilla Albers A, Asafu-Adjei J, Delaney MK, et al: Episodic memory of odors stratifies Alzheimer biomarkers in normal elderly. Annals of Neurology, Dec. 2016
Quarmley M, Moberg PJ, Mechanic-Hamilton D, et al: Odor Identification Screening Improves Diagnostic Classification in Incipient Alzheimer’s Disease. Journal of Alzheimer’s Disease, published online Nov. 18, 2016