Alzheimer's, dementia might be discovered using the smell test

It’s been said the nose knows—but new research details just how much our sniffers can tell us. Two studies presented July 26 at the Alzheimer’s Association International Conference examined changes in odor identification as a precursor for cognitive decline or transition to dementia.

One project drew a connection with cognitive decline with decreased ability to identify odors. Seonjoo Lee, PhD, and colleagues from Columbia University Medical Center administered a smell test to 397 people with an average age of 80 years old. The research team conducted a MRI scan and followed the subjects for four years.

Eventually, 50 of them (12.6 percent) transitioned to dementia (49 to Alzheimer’s) and nearly 20 percent were considered in cognitive decline. Lower scores on the 40-item University of Pennsylvania Smell Identification Test (UPSIT) were significantly associated with dementia and Alzheimer’s disease.

Entorhinal cortical thickness was significantly associated with lower test scores among participants who developed dementia, but the test scores were more predictive of cognitive decline among the participants.

“Our research showed that odor identification impairment, and to a lesser degree entorhinal cortical thickness, were predictors of the transition to dementia,” Lee said. “These findings support odor identification as an early predictor, indirectly suggesting that impairment in odor identification may precede thinning in the entorhinal cortex early in clinical stage of Alzheimer’s disease.”

The second study was conducted by William Kreisl, MD, and colleagues from Columbia University Medical Center. This research examined the utility of odor identification impairment and beta amyloid PET or CSF analysis in predicting memory decline.

Kreisl’s team determined a UPSIT score and amyloid status for 84 individuals in the study. (58 with mild cognitive impairment and 26 control subjects).

After six months, 67 percent showed decline in memory. After corrective for age, sex and education, the researchers found amyloid-positivity determined by PET scan or lumbar puncture predicted decline, while UPSIT scores did not. Those with UPSIT scores below 35, though, were three times more likely to experience memory decline.

“Our research suggests that both UPSIT score and amyloid status predict memory decline,” Kreisl said. “Younger age, higher education and shorter follow-up may explain why UPSIT did not predict decline as strongly in this study as in previous studies.”

The research team recommended further investigation into the predictive abilities of UPSIT scores, because the memory test is much less expensive and easier to conduct than PET imagining or lumbar puncture.