Olfactory skills may be key to early, accurate Alzheimer's diagnoses

In elderly patients, a ‘sniff test’ may help clinicians in the accurate and early diagnosis of Alzheimer’s disease, as well as in the diagnosis of mild cognitive impairment (MCI), according to results from researchers at the Perelman School of Medicine, University of Pennsylvania, who recently published their research in the December 20 issue of the Journal of Alzheimer’s Disease.

Their research offers hope to the many older adults affected by mild cognitive impairment who are not identified due, in part, to the lack of adequate screening.

“There’s the exciting possibility here that a decline in the sense of smell can be used to identify people at risk years before they develop dementia,” said principal investigator David R. Roalf, PhD, assistant professor, department of psychiatry, University of Pennsylvania. “These results suggest that a simple odor identification test can be a useful supplementary tool for clinically categorizing MCI and Alzheimer’s, and even for identifying people who are at the highest risk of worsening.”

For their study, Dr. Roalf and colleagues used the Sniffin’ Sticks Odor Identification Test in 728 elderly people, who also completed a standard cognitive test (the Montreal Cognitive Assessment). Subjects had been previously evaluated with several neurological tests, and then classified as “healthy older adult,” “mild cognitive impairment,” or “Alzheimer’s dementia.” These classifications were then validated with the cognitive test or with the cognitive test combined with the sniff test.

Healthy older adults (n=292) had higher odor identification scores compared to those with mild cognitive impairment (n=174) and those with Alzheimer’s dementia (n=262). Those with mild cognitive impairment also had higher scores than subjects with Alzheimer’s dementia.

When added to the cognitive test, the sniff test added significant diagnostic accuracy. They found that while the cognitive test alone correctly classified only 75% of people with MCI, when the sniff test was added, this rose to 87%.

Smell tests are already being used to assess elderly patients in a few large, dementia clinics, but one reason testing is not more widespread is the lengthiness of the test itself. To overcome this, Dr. Roalf and his fellow researchers have been working on developing a shorter test that is as accurate as the longer ones.

“We’re hoping to shorten the Sniffin’ Sticks test, which normally takes 5 to 8 minutes, down to 3 minutes or so, and validate that shorter test’s usefulness in diagnosing MCI and dementia—we think that will encourage more neurology clinics to do this type of screening,” said Dr. Roalf.

In addition, they plan more studies on the possibility that the protein markers of Alzheimer’s disease, already present in the olfactory region of the brain before dementia sets in, may be detectable in nasal fluid.

This study was funded by the National Institute of Mental Health (K01 497 MH102609), National Institute on Aging (P30 AG10124), and the Penn Center of Excellence for Research on Neurodegenerative Diseases.