COPENHAGEN—Greater neurodegeneration is associated with worse olfactory function among clinically normal elderly persons who have an elevated level of cortical amyloid, researchers reported at the 2014 Alzheimer’s Association International Conference. The finding suggests that a smell test could potentially be used to screen for Alzheimer’s disease, according to Matthew E. Growdon, and colleagues.
In a study that included 215 participants from the Harvard Aging Brain study, the investigators administered the University of Pennsylvania Smell Identification Test (UPSIT) and measured hippocampal volume and entorhinal cortex thickness with MRI, as well as amyloid burden using Pittsburgh compound B (PiB) PET. In addition, all participants underwent neuropsychologic testing.
Mr. Growdon’s group found that worse olfactory function was significantly associated with decreased hippocampal volume and entorhinal cortex thickness, and it was marginally associated with PiB positive status. A multivariate model revealed that a thinner entorhinal cortex in PiB-positive patients was significantly associated with worse olfactory function. Furthermore, unadjusted analyses showed that better olfactory function was associated with better memory performance.
“Our research suggests that there may be a role for smell identification testing in clinically normal older individuals who are at risk for Alzheimer’s disease,” stated Mr. Growdon, an MD candidate at Harvard Medical School and the Harvard School of Public Health in Boston. “For example, it may prove useful to identify proper candidates for more expensive or invasive tests. Our findings are promising but must be interpreted with caution. These results reflect a snapshot in time. Research conducted over time will give us a better idea of the utility of olfactory testing for early detection of Alzheimer’s disease.”
Predicting Transition From MCI to Alzheimer’s Disease
In a separate study, Davangere Devanand, MD, and colleagues found that odor identification deficits were associated with the transition from mild cognitive impairment (MCI) to Alzheimer’s disease in nondemented elderly persons. The researchers analyzed data from 1,037 persons from the North Manhattan study who did not have dementia at their initial evaluation. All participants (mean age, 80.7; 68% female; 34% Caucasian) had two follow-ups at two-year intervals. UPSIT scores were higher in cognitively intact subjects compared with scores among participants with nonamnestic MCI, and higher in persons with nonamnestic MCI compared with scores among those with amnestic MCI. During the follow-up, 64 persons were diagnosed with dementia, 58 were diagnosed with Alzheimer’s disease, and 270 people died.
Among the 757 persons who were followed, lower odor identification scores on UPSIT were significantly associated with the transition to dementia and Alzheimer’s disease, after the researchers controlled for APOE genotype.
The risk of Alzheimer’s disease increased by about 10% for each point lower that a person scored on the UPSIT, noted Dr. Devanand, Director of the Division of Geriatric Psychiatry, New York State Psychiatric Institute and Professor of Psychiatry and Neurology at the College of Physicians and Surgeons, Columbia University, in New York City.
Lower baseline UPSIT scores—but not measures of verbal memory—were significantly associated with cognitive decline in participants without baseline cognitive impairment, noted Dr. Devanand.
“Odor identification deficits were associated with the transition to dementia and Alzheimer’s disease and with cognitive decline in cognitively intact participants in our community sample,” Dr. Devanand commented. “The test was effective in English and Spanish. If further large-scale studies reproduce these results, a relatively inexpensive test such as odor identification may be able to identify subjects at increased risk of dementia and Alzheimer’s disease at a very early stage, and may be useful in identifying people at increased risk of cognitive decline more broadly.”
—Colby Stong