Conference Coverage
TORONTO—Impairment in odor identification is a strong predictor of the transition to dementia, according to data described at the Alzheimer's Association International Conference. Entorhinal cortical thickness also predicts the transition to dementia, albeit to a lesser degree.
In addition, impaired odor identification, but not entorhinal cortical thickness, appears to predict cognitive decline. These results may provide indirect evidence that olfactory impairment precedes entorhinal cortical thinning, said Seonjoo Lee, PhD, Assistant Professor of Clinical Biostatistics in Psychiatry at Columbia University Mailman School of Public Health in New York.
The olfactory system undergoes structural and functional changes in the early stage of Alzheimer's disease. Dr. Lee and colleagues examined participants in the Washington Heights Community Aging Project II to determine whether the University of Pennsylvania Smell Identification Test (UPSIT) score predicts transition to dementia or cognitive decline. The investigators also sought to compare UPSIT score as a biomarker with entorhinal cortical thickness. Eligible participants were older than 65, did not have dementia, and underwent MRI and UPSIT at baseline. The researchers enrolled 397 subjects in the study and followed them for four years.
In all, 50 participants developed dementia during follow-up, including 49 people who developed Alzheimer's disease. Dr. Lee and colleagues measured average entorhinal cortical thickness using FreeSurfer and tested UPSIT and its interaction with entorhinal cortical thickness as the main effects.
The researchers measured participants' cognition by evaluating memory, language, and visuospatial cognition. They defined cognitive decline as a decline of one or more standard deviations in any of these cognitive domains during the four-year follow-up. In the examinations of incident dementia and cognitive decline, Dr. Lee and colleagues adjusted the data for age, gender, years of education, functional status, intracranial volume, and language of UPSIT administration.
UPSIT score, entorhinal cortical thickness, and these factors' interactions significantly predicted the transition to dementia. As UPSIT score declined, subjects were more likely to develop dementia. The same association was found for entorhinal cortical thickness. Among participants with olfactory impairment, thinning in the entorhinal cortex increased the risk of incident dementia.
In contrast, only UPSIT was a strong predictor of cognitive decline. Dr. Lee also found that entorhinal cortical thickness was significantly associated with UPSIT score only among subjects who transitioned to dementia. "This [result] confirmed that those two biomarkers are associated with each other for dementia," she said. The correlation also indicates that odor identification deficits are related to neurodegenerative changes in the entorhinal cortex during the progression of Alzheimer's disease, she added.
—Erik Greb