Loss of Smell Could Indicate Early Stages of Alzheimer's

Research finds that older patients with lower odor identification test scores were at increased risk of Alzheimer’s disease and dementia.

A decreasing sense of smell may indicate cognitive impairment and the development of Alzheimer’s disease, according to the results of 2 studies presented on July 13, 2014, at the Alzheimer’s Association International Conference 2014 in Copenhagen, Denmark.

In the first study, Matthew E. Growdon, BA, MD/MPH candidate at Harvard Medical School and Harvard School of Public Health, and colleagues assessed the relationship between the sense of smell, memory performance, loss of brain cell function, and amyloid deposition in 215 elderly patients enrolled in the Harvard Aging Brain Study. Patients completed the University of Pennsylvania Smell Identification Test (UPSIT) in addition to several cognitive tests. The researchers measured amyloid deposits in the brain and the size of the entorhinal cortex and the hippocampus.

The results indicated that a smaller hippocampus and a thinner entorhinal cortex were significantly associated with lower scores on the smell identification and memory tests. The researchers of the study separately analyzed a subgroup of patients with elevated levels of amyloid and found that a thinner entorhinal cortex was significantly associated with a decreased sense of smell, after adjusting for age, gender, and other potential cofounders.

“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,” Growden said in a press release. “For example, it may prove useful to identify proper candidates for more expensive or invasive tests.”

Similar results were found in the second study. The researchers of the study followed 757 elderly patients in New York City during 3 time periods—from 2004 to 2006, 2006 to 2008, and 2008 to 2010. Patients received a variety of cognitive tests throughout the study periods and completed the UPSIT between 2004 and 2006.

During the study, 109 patients were diagnosed with dementia and 270 patients died. Overall, the results indicated that lower odor identification scores were significantly associated with the development of dementia and Alzheimer’s, after controlling for confounding variables. For each point lower that patients scored on the UPSIT, the risk for Alzheimer’s increased by approximately 10%. In addition, lower scores on the UPSIT at baseline were significantly associated with cognitive decline in patients without impairment at baseline.

“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, said the lead author of the study, Davangere Devanand, MBBS, MD, in a press release.

Although both studies resulted in similar findings, the authors of both suggest that studies with larger sample sizes and longer follow-up times are needed to validate the outcomes.