Could Decreased Sense of Smell Indicate Dementia Onset?

A new study finds a connection between a decreased sense of smell and the onset of some types of dementia.

In a study of 1,430 cognitively normal individuals, a team led by Mayo Clinic researchers evaluated participants’ sense of smell. Roughly half of the patients taking part were men and approximately half were women, with an average participant’s age of 79.5 years. Patients were enrolled in the population-based, prospective study between the years 2004 and 2010, and were clinically assessed at baseline and again every 15 months through the year 2014.
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The test the authors used to evaluate patients included 6 food-related and 6 non-food related smells—banana, chocolate, cinnamon, gasoline, lemon, onion, paint thinner, pineapple, rose, soap, smoke, and turpentine—with participants scratching, sniffing, and choosing one of 4 options for their scores to be compiled.

The team, led by Rosebud Roberts, MB, ChB, an epidemiologist at the Mayo Clinic in Rochester, Minn., identified 250 new cases of mild cognitive impairment (MCI) among the 1,430 patients, over an average follow-up period of 3.5 years. Roberts and colleagues also found a link between a diminished ability to identify smells and a greater risk of amnestic MCI (aMCI). No link was established, however, between a lesser sense of smell score and non-amnestic MCI (naMCI), which, as the authors note, can impact other thinking skills. In addition, the investigators reported 64 dementia cases among 221 patients with prevalent MCI, and an association between the worst smell test score categories and a progression from aMCI to Alzheimer’s disease dementia.

Ultimately, the findings suggest that the smell identification test is a marker for risk of incident mild cognitive impairment, as well as a progression from mild cognitive impairment to dementia, says Roberts.

“This test is not diagnostic,” adds Roberts, “but for the primary practitioner trying to determine if an individual is at risk for Alzheimer’s dementia, the test provides additional information to help make the decision.”

The test, she says, “is easily administered in the outpatient setting, is non-invasive, and has population-norms by age and sex to determine abnormality. Thus, the smell test can help the physician provide targeted intervention to prevent progression, including pharmacologic treatments, where possible.”

—Mark McGraw

Reference

Roberts R, Christianson T, et al. Association Between Olfactory Dysfunction and Amnestic Mild Cognitive Impairment and Alzheimer Disease Dementia. JAMA Neurol. 2015.