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Alzheimer's, Dementia & Mental Health
Senior Citizens with Problems Identifying Smells may
begin Cognitive Decline to Alzheimer’s
Other researchers developing medical device to sniff
out olfactory disorders
July 3, 2007 – In an update on earlier research, a
study has found that older people who have difficulty identifying common
odors may have a greater risk of developing problems with thinking,
learning and memory, or mild cognitive impairment. Previous research had
found a smell test could help identify which people with MCI are most
likely to develop Alzheimer’s disease.
Mild cognitive impairment (MCI) - or a decline in
thinking, learning and memory abilities - is increasingly recognized as
a precursor to Alzheimer’s disease, according to background information
in the article in the July issue of Archives of General Psychiatry, one
of the JAMA/Archives journals.
Although, MCI does not always progress to dementia
or even persist, with large numbers of persons reverting back to normal
cognitive performance.
Impairments in the ability to recognize odors have
been associated with more rapid cognitive decline and also with the
development transition from mild cognitive impairment to Alzheimer’s
disease. However, little is known about factors that predict the
development of mild cognitive impairment.
Robert S. Wilson, Ph.D., of Rush University Medical
Center, Chicago, and colleagues studied 589 older adults (average age
79.9) who did not have cognitive impairment in 1997.
At that time, the participants took a smell
identification test, during which time 12 familiar odors were placed
under their nose.
Note: See story below this article about the
development of a medical device to test smell.)
The 12-item Brief Smell Identification Test used in
this study is marketed by Sensonics. It uses the odorants of banana,
chocolate, cinnamon, gasoline, lemon, onion, paint thinner, pineapple,
rose, soap, smoke, and turpentine.
They were asked to match each odor to one of four
possible alternatives, and were scored from one to 12 based on the
number of correct responses.
At the beginning of the study and again every year
for up to five years, the participants underwent a clinical evaluation
that included a medical history, neurological examination and testing of
their cognitive function.
During the study, 177 individuals (30.1 percent)
developed mild cognitive impairment. Risk of developing mild cognitive
impairment increased as odor identification decreased, so that those who
scored below average (eight) on the odor identification test were 50
percent more likely to develop the condition than those who scored above
average (11).
This association did not change when stroke,
smoking habits or other factors that might influence smell or cognitive
ability were considered. Impaired odor identification was also
associated with lower cognitive scores at the beginning of the study and
with a more rapid decline in episodic memory (memory of past
experiences), semantic memory (memory of words and symbols) and
perceptual speed.
“The neurobiological bases of age-associated
olfactory dysfunction are uncertain,” the authors write.
Evidence suggests that even before the symptoms of
Alzheimer’s disease develop, hallmark tangles develop in certain areas
of the brain that may be associated with the processing of smells.
Because difficulty identifying odors is associated with other
neurological diseases, including Parkinson’s disease, other mechanisms
are likely involved.
The present findings build on previous research by
showing that difficulty in identifying odors predicts not only the
transition from MCI to AD but also the transition from normal cognition
to MCI. This latter finding is important: by the time persons meet the
criteria for MCI, they are already exhibiting the primary clinical
manifestation of AD, accelerated cognitive decline and the
neuropathologic hallmarks of the disease, consistent with the idea that
MCI is a symptom indicating the onset of AD.
The results of this and other prospective studies
suggest it may be possible to identify subsets of older subjects without
cognitive impairment who are at increased risk for developing MCI and
AD.
“Further clinicopathological and
clinicoradiological research on age-related olfactory dysfunction is
needed,” they continue.
“Among older persons without manifest cognitive
impairment, difficulty in identifying odors predicts subsequent
development of mild cognitive impairment,” the authors conclude.
“The findings suggest that olfactory dysfunction
can be an early manifestation of Alzheimer’s disease … and that
olfactory assessment may be useful for early disease identification.”
Editor’s Note: This study was supported by
grants from the National Institute on Aging and by the Illinois
Department of Public Health. Please see the article for additional
information, including other authors, author contributions and
affiliations, financial disclosures, funding and support, etc.
New Medical Device Can Sniff Out Serious Health
Problems
In April, University of Cincinnati researchers
announced a new medical device is in development to sniff out olfactory
disorders that could be an early warning of Alzheimer’s disease,
Parkinson’s disease and other problems outside the typical sensory loss
associated with aging.
The Sniff Magnitude Test (SMT), an invention of UC
Psychology Professor Robert Frank and Professor Emeritus Robert
Gesteland of the UC Department of Cell Biology, is now under further
development with the WR Medical Electronics Company in Stillwater, Minn.
The company will manufacture and market the test.
The Sniff Magnitude Test project, a creation that
was seven years in the making, was awarded a total of $1,340,098 from
the National Institutes of Health in developmental funding. UC
Psychology Professor Robert Frank says that in the near future, UC
researchers will begin testing five different prototypes of the SMT
built by WR Medical Electronics. Currently, Frank says an earlier model
of the SMT is being tested in a high-profile clinic in Germany as well
as at the University of Pennsylvania. Frank says the SMT customer base
would be primarily otolaryngologists and neurologists.
“The whole test is based on the very simple
observation that when you sniff and you detect a smell, you take a
smaller sniff than if you inhaled and didn’t detect a smell,” Frank
explains. “For someone with normal sense of smell, the size of the sniff
when detecting an odor is cut in half. For someone who cannot detect
odor, the size of the sniff for just air and the size of the sniff for
an odor are the same.”
In humans, Frank says the sense of smell is one of
our less robust senses. He says it’s more susceptible to harm because
there is less neurological machinery in the brain devoted to processing
the sense of smell. “So, that’s the reason it might be acting a little
bit like the canary in the mineshaft. Because it’s more fragile, when
you have insult to the brain, it may be sensitive to loss earlier in the
disease process.”
Frank adds that because smells don’t have to be
identified as part of the Sniff Magnitude Test, the test can be used on
adults as well as children (who may be too young to link a smell with a
name) and people representing international cultures (who are unfamiliar
with some common odors in the U.S.). “What’s also unique about this test
is that it does not require a good memory, which is an issue in testing
people with Alzheimer’s or some other dementia-related disease,” Frank
says. “For instance, other tests ask, ‘Does this smell like garlic?’ or,
‘Does this smell like tar, or roses?’ Once there’s a problem with
memory, this kind of test would be difficult.”
So what does it mean if a child, or someone
unlikely to have an age-related disease, flunks the sniff test? “If they
fail our test, that’s a pretty good indication that there’s something
wrong with their sense of smell. Maybe there’s an obstruction – a
deviated septum or polyps,” Frank says. “Perhaps the olfactory nerve has
been damaged due to a head injury or a viral infection.”
For those who are proud of their keen sense of
smell, this is not a test to tickle their senses. Because the really
nasty smells worked best for the Sniff Magnitude Test, Frank says the
test subjects get a whiff of three odors: a blend of ripe cheese and
rancid meat, a fragrance that combines a burning smell with a skunk-like
smell, and amyl acetate, which smells like banana. “You have to get
people to really suppress the sniff and that’s why the bad odors work so
well,” explains Frank. “To a certain extent, we put the banana smell in
there to give them a little break.”
Frank adds that his current research is exploring
the patterns of loss of smell that could be an indicator of Alzheimer’s.
He says the Sniff Magnitude Test is also getting a look by researchers
at the Rush University Medical Center in Chicago as part of a major
epidemiological study on aging, Alzheimer’s disease and sense of smell.
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