How Rapid loss of smell may predict dementia and smaller brain areas linked to Alzheimer's

Researchers at the University of Chicago Medicine have discovered another reason to appreciate our sniffers. Not only can a decline in a person's sense of smell over time predict their loss of cognitive function, but it can also foretell structural changes in regions of the brain important in Alzheimer's disease and dementia.

The findings, based on a longitudinal study of 515 older adults published July 2 in Alzheimer's & Dementia: The Journal of the Alzheimer's Association, could lead to the development of smell-test screening to detect cognitive impairment earlier in patients.

It's estimated more than 6 million Americans have Alzheimer's disease, which is characterized by memory loss and other symptoms, such as mood changes and trouble completing everyday tasks. There is no cure for Alzheimer's, but some medications can temporarily slow its symptoms.

Memory plays a critical role in our ability to recognize smells, and researchers have long known a link between the sense of smell and dementia. The plaques and tangles that characterize tissue affected by Alzheimer's disease often appear in olfactory and memory-associated areas before developing in other parts of the brain. It's still unknown if this damage actually causes a decline in a person's sense of smell.

Jayant M. Pinto, MD, a professor of surgery at the University of Chicago and ENT specialist who studies olfactory and sinus disease, and his team wanted to see whether it was possible to identify alterations in the brain that correlated with a person's loss of smell and cognitive function over time.

The team tapped anonymized patient data from Rush University's Memory and Aging Project (MAP), a study group begun in 1997 to research chronic conditions of aging and neurodegenerative disease such as Alzheimer's disease.

The UChicago Medicine scientists found that a rapid decline in a person's sense of smell during a period of normal cognition predicted multiple features of Alzheimer's disease, including smaller gray matter volume in the areas of the brain related to smell and memory, worse cognition and higher risk of dementia in these older adults. In fact, the risk of sense of smell loss was similar to carrying the APOE-e4 gene, a known genetic risk factor for developing Alzheimer's.

The changes were most noticeable in the primary olfactory regions, including the amygdala and entorhinal cortex, which is a major input to the hippocampus, a critical site in Alzheimer's disease.

Ref:

Rachel Pacyna et. al, Rapid olfactory decline during aging predicts dementia and GMV loss in AD brain regions, Alzheimer s & Dementia, DOI: 28-Jul-2022,10.1002/alz.12717