Sense of smell could be an effective way to predict Alzheimer’s disease

New research published in the journal Annals of Neurology suggests an individual's sense of smell could be useful in determining whether they are likely to develop Alzheimer's disease

smell-alzheimersPrincipal investigator Dr. Mark Albers, of the Department of Neurology at Massachusetts General Hospital (MGH), and team found that by assessing the ability to recognize, recall, and distinguish different odors, they could accurately identify individuals who were at greater risk of Alzheimer’s disease.

Alzheimer’s is the most common form of dementia, with around 5.4 million adults in the United States living with the disease. By 2050, this number is expected to reach 13.8 million, unless new preventive and treatment strategies are found.

As with any illness, the earlier Alzheimer’s is detected, the greater the chance of treatment success. However, at present, Alzheimer’s can only be identified through a series of medical and cognitive assessments, and it can often take years to receive a clinical diagnosis.

According to Dr. Albers and colleagues, it is known that Alzheimer’s disease can negatively impact the brain circuits that control sense of smell, or olfaction, and studies have suggested that such neurodegeneration can arise more than a decade before the onset of memory problems.

With this in mind, the researchers set out to investigate whether testing a person’s sense of smell could be an effective way to predict Alzheimer’s disease.

Olfactory recognition and recall assessed with four tests

Dr. Albers and team included 183 older adults in their study, all of whom were part of ongoing studies taking place at the Massachusetts Alzheimer’s Disease Research Center, based at MGH.

Of these participants, 70 had normal cognitive functioning, 74 had subjective cognitive impairment (whereby a person reports memory and thinking problems, but these cannot be verified with cognitive tests), 29 had mild cognitive impairment (MCI), and 10 had Alzheimer’s disease.

All participants had undergone in-depth medical and neurological assessments, as well as brain imaging to pinpoint features associated with Alzheimer’s disease.

Each subject took part in four separate tests created by the MGH team that assessed their sense of smell: the Odor Percept IDentification-10 (OPID-10) test, the Odor Awareness Scale (OAS), the OPID-20 test, and the Odor Discrimination (OD) test.

The OPID-10 test requires participants to smell 10 different odors – including menthol, clove, strawberry, smoke, and lemon – for 2 seconds and report whether each scent is familiar. They are then asked to choose one of four words that best describes each odor.

In the OPID-20 test, subjects are asked to smell the same 10 odors from the OPID-10 test, as well as a further 10, which include banana, garlic, cherry, peach, and chocolate. Participants are asked whether they were presented with any of these odors in the OPID-10 test, as a way of determining their olfactory recall. Based on their answers, they are given precepts of odor episodic memory (POEM) score.

The OAS is a questionnaire used to determine participants’ attention to odors in the environment and how scents affect their behavior and emotions, while the OD test assesses subjects’ ability to repeatedly distinguish between two different odors.

Poorer sense of smell linked to features of Alzheimer’s

Using the four tests, the researchers found they could accurately distinguish between each of the four groups of study participants.

In detail, participants who performed poorly on the OPID-20 test were more likely to show thinning in two regions of the brain: the hippocampus and the entorhinal cortex. Such brain changes have been associated with Alzheimer’s disease.

What is more, the researchers found they could differentiate between participants with normal cognitive functioning and those with Alzheimer’s using POEM scores, with lower scores associated with greater cognitive decline.

The team notes that in adults with normal cognitive functioning, the ability to recognize and distinguish scents can vary widely.

To account for this variance, the researchers compared the POEM scores of the groups with normal cognitive function and subjective cognitive impairment with predicted scores, based on their results in the OD and OAS tests. This, they say, enabled better identification of which individuals were good or bad at recalling and recognizing odors.

Source: Medical News Today