Two studies released at an international Alzheimer's meeting Tuesday suggest doctors may eventually be able to screen people for this form of dementia by testing the ability to identify familiar odors, like smoke, coffee and raspberry.
In both studies, people who were in their 60s and older took a standard odor detection test. And in both cases, those who did poorly on the test were more likely to already have — or go on to develop — problems with memory and thinking.
"The whole idea is to create tests that a general clinician can use in an office setting," says Dr. William Kreisl, a neurologist at Columbia University, where both studies were done. The research was presented at the Alzheimer's Association International Conference in Toronto.
Currently, any tests that are able to spot people in the earliest stages of Alzheimer's are costly and difficult. They include PET scans, which can detect sticky plaques in the brain, and spinal taps that measure the levels of certain proteins in spinal fluid.
The idea of an odor detection test arose, in part, from something doctors have observed for many years in patients with Alzheimer's, Kreisl says.
"Patients will tell us that food does not taste as good," he says. The reason is often that these patients have lost the ability to smell what they eat.
That's not surprising, Kreisl says, given that odor signals from the nose have to be processed in areas of the brain that are among the first to be affected by Alzheimer's disease.
But it's been tricky to develop a reliable screening test using odor detection.
So Kreisl and a team of researchers studied 84 people in their 60s and 70s, including 58 with the sort of memory problems that suggest early Alzheimer's.
The participants took something called the University of Pennsylvania Smell Identification Test, or UPSIT.
"It's basically a set of cards," Kreisl says. "And each card has a little scratch and sniff test on it." The cards feature familiar odors like coffee, chocolate, cinnamon and licorice.
The study found that people who had trouble identifying odors were three times more likely than other people to have memory problems. Moreover, the odor test "was able to predict memory decline in older adults about as well as the PET scan or spinal tap," Kreisl says.
A second study by another team from Columbia followed, for more than four years, 397 people whose average age was 80 at the start. Their scores on the odor test were a good predictor of which people were most likely to go on to develop dementia, the researchers found.
The odor tests aren't perfect. For one thing, other degenerative brain diseases, including Parkinson's, can also affect odor detection. Also, the ability to smell can be diminished by smoking, certain head injuries and even normal aging.
So researchers are looking at other "biomarkers" of Alzheimer's, including some changes that affect the eye.
"The eye has nerves that are very closely linked to the brain," says Maria Carrillo, chief science officer of the Alzheimer's Association. So changes in those nerves can help reveal early Alzheimer's.
But all the screening tests for Alzheimer's are of limited value, Carrillo cautions, because there is still no drug that can slow or halt the disease.
"What we really need," she says, "is to be able to use these screening tools at the same time that we have a therapeutic."
ROBERT SIEGEL, HOST:
It may one day be possible to detect early-stage Alzheimer's through a simple sniff test. New research links a person's mental decline to their ability to identify odors like licorice and chocolate. NPR's Jon Hamilton reports.
JON HAMILTON, BYLINE: People with Alzheimer's often have a surprising complaint. William Kreisl, a neurologist at Columbia University, says it has to do with food.
WILLIAM KREISL: Patients will tell us that food does not taste as good early on in certain brain conditions.
HAMILTON: Food is less tasty because these patients have lost the ability to smell what they eat. And Kreisl says that's often because odor signals coming from the nose have to be processed in vulnerable areas of the brain.
KREISL: Areas of the brain that degenerate early on Alzheimer's disease.
HAMILTON: So scientists have wondered whether it might be possible to use odor detection to identify people in the early stages of Alzheimer's. To find out, Kreisl lead a team that studied 84 people in their 60s and 70s. Some already had developed problems with memory and thinking. The participants took something called the University of Pennsylvania Smell Identification Test, or UPSIT.
KREISL: It's basically a set of cards. And each card has a little scratch-and-sniff test on it. The patient scratches that little button and then smells. And just like a kid's scratch-and-sniff book, there'll be different odors that are on each page.
HAMILTON: Familiar odors like coffee, chocolate, cinnamon and licorice. Sure enough, people who did poorly on the test were three times more likely than people who did well to have memory problems. Then, Kreisl says, the team looked to see how odor detection compared with more costly and difficult methods of detecting signs of Alzheimer's. They picked PET scans and spinal taps.
KREISL: What we found was that a low score on the UPSIT was able to predict memory decline in older adults about as well as the PET scan or by spinal tap.
HAMILTON: A second study by another team at Columbia found that the odor test scores also predicted which people were most likely to develop dementia. The research was presented today at the Alzheimer's Association International Conference in Toronto. Kreisl says odor detection might eventually offer a quick and inexpensive way to help spot Alzheimer's.
KREISL: The whole idea is to create tests that a general clinician could use in an office setting that would give us really meaningful information as far as understanding what's going on and how to prepare for the future.
HAMILTON: But the odor tests aren't perfect. Other brain diseases, including Parkinson's, can also affect odor detection. Also, the ability to smell can be diminished by smoking, certain head injuries and even normal aging. So researchers are looking at other so-called biomarkers of Alzheimer's, including some that are present in the eye. Maria Carrillo, chief science officer of the Alzheimer's Association, says that makes sense.
MARIA CARRILLO: The eye has nerves that are very closely linked to the brain. And picking up those changes in the nerves of the eye can indeed tell us a lot of what's going on in the brain.
HAMILTON: But Carrillo says all the tests will mean a lot more when there is a drug that can actually halt or slow down Alzheimer's disease. Jon Hamilton, NPR News. Transcript provided by NPR, Copyright NPR.