By Eric McDade, D.O.
Although we take it for granted, our sense of smell relies
on an impressive level of complexity that not only allows us to experience the
world around us, but also puts it at risk for injury through a number of
different ways. Most of us are familiar
with the incredible experience of being immediately transported back to a
previous place or time after smelling a special scent. Researchers in Alzheimer’s
dementia and other related disorders such as Parkinson’s
have found that our
sense of smell might be helpful in detecting brain changes associated with
these and other illnesses.
Based on this, researchers led by Dr. Kenneth Heilman, professor
of Neurology, and Jennifer Stamps, a graduate student in the McKnight Brain
Institute Center for Smell and Taste at the University of Florida, have
recently published an interesting study looking at the usefulness of peanut butter
in diagnosing Alzheimer’s dementia from
types of dementias. The paper published in the Journal of Neurological Sciences
used a very simple approach.
Here’s the experiment:
- Patients coming in for Alzheimer’s
testing were asked to close their eyes and mouth and block one nostril.
- A clinician then held out one
tablespoon of peanut butter at the end of a metric ruler and moved the peanut
butter up one centimeter at a time until the patient could detect the smell.
- After the distance was recorded,
the same procedure was repeated on the other nostril.
The experiment was then repeated in older people in three
categories: those with mild memory problems (referred to as mild cognitive impairment
those with memory problems felt to be from other dementias, and those without memory
What they found was that the group diagnosed with Alzheimer’s dementia had a
much greater difficulty smelling the peanut butter with their left nostril
compared to the right nostril, whereas
in the normal volunteer group both sides were nearly equal in detecting the
smell. Also, in about half of the group
with mild cognitive impairment- which represents a group with a risk of
developing dementia- they found a pattern similar to those with Alzheimer’s
Based on these findings, researchers proposed that this
relatively straightforward, simple test might be useful in the clinic to confirm
a diagnosis of Alzheimer’s dementia, especially early on when the symptoms are
still relatively mild, and in clinics where access to more sophisticated
testing is not available. However, what
was not emphasized was that there are a
number of things that can affect the sense of smell and that based on this
study people should not assume that a change in smell means they are developing
It is critically important to keep in mind that the sense of
smell can be affected by a large number of things including medications,
allergies, environmental exposures and, importantly, our sense of taste! Readers should not think that because their
sense of smell has changed that they have Alzheimer dementia.
What makes this study unique and intriguing is how simple
the test was and how the large differences were between the groups. However,
important limitations of the study include that those diagnosed with Alzheimer’s
dementia were more cognitively impaired than the other groups which could
account for some of the results. Also, there was a group of patients with the
opposite pattern, where the right side was more affected than the left
side. Lastly, they excluded anyone that
could have problems with their sense of smell for other reasons. Although the research is exciting, future
research will require larger groups of people to be tested and for the diagnosis
to be confirmed.
As most of us involved in dementia and neuroscience research
understand, the mind is beautiful yet incredibly complex. Rarely is there a “simple”
explanation or answer to a disorder as complex as Alzheimer’s. However, this
study does support further research into disorders of smell in Alzheimer’s and
other types of dementia. It also reminds us of the importance of identifying
practical, inexpensive tests that could be used to help diagnose Alzheimer’s.
Eric M. McDade, DO,
is an assistant professor of Neurology at the University of Pittsburgh School
of Medicine, and associate director of the Clinical Core of Pitt’s Alzheimer
Disease Research Center.