Can Sense of Smell Foreshadow Alzheimer Risk?

According to a new study led by Massachusetts General Hospital researchers, a person’s sense of smell could be helpful in determining his or her likelihood of developing Alzheimer disease.

Investigators sought to relate a novel test of identifying and recalling odor percepts to biomarkers of Alzheimer disease in well-characterized elderly individuals, ranging from cognitively normal to demented. The authors studied 183 participants who were taking part in ongoing studies at the Massachusetts Alzheimer's Disease Research Center. Among these patients, 70 had normal cognitive functioning, while 74 experienced subjective cognitive impairment. Another 29 had mild cognitive impairment (MCI), while 10 had been diagnosed with Alzheimer disease. Extensive medical and neurologic assessments were done for all participants, who had also undergone brain imaging to identify features linked to Alzheimer disease.

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To assess participants' sense of smell, the authors required patients to take part in tests such as the Odor Percept Identification-10 (OPID) and the Percepts of Odor Episodic Memory (POEM) tests. The OPID-10 test, for example, asked participants to smell 10 different odors, including menthol, strawberry, clove, and lemon, and to subsequently use 1 of 4 words to describe each odor.

Overall, accuracy of identification and episodic memory of odor percepts differed significantly across diagnosis and age, with progressively worse performance across degrees of impairment. Among the participants who were cognitively normal or had subjective cognitive concerns, poorer than expected performance on the POEM test was associated with higher frequencies of the APOE ε4 allele, thinner entorhinal cortices, and worse longitudinal trajectory of Logical Memory scores.

"Alzheimer disease begins at least 15 years before the onset of memory symptoms. Following the paradigm of cancer screening, we and other groups are working to develop accessible, affordable, precise, predictive screens for Alzheimer in healthy elders," said principal investigator Mark W. Albers, MD, PhD, a neurologist at Massachusetts General Hospital and an assistant professor of neurology at Harvard Medical School.

Successful screening "will afford therapeutic interventions in healthy individuals, which has been a successful preventive and treatment paradigm throughout multiple fields of medicine," Dr Albers said. "In the future, we hope that these screens will take part during the annual checkups in primary care physicians' offices or in the patient's home, where the first line of communication of positive screen results will be with primary care physicians."

—Mark McGraw

Reference:

Albers AD, Asafu-Adjei J, Delaney MK, et al. Episodic memory of odors stratifies Alzheimer biomarkers in normal elderly [published online October 1, 2016]. Ann Neurol. doi:10.1002/ana.24792.