Misidentified sniffs may point to early-stage Alzheimer’s

Mayo Clinic researchers have found a correlation between neuroimaging biomarkers of Alzheimer’s disease and results from a literal smell test: If at-risk older folks are losing their sense of smell, they’re more likely to be developing the disease than their well-smelling peers.

In a study published online May 22 in Annals of Neurology, lead author Maria Vassilaki, MD, MPH, PhD, and colleagues describe their work evaluating 829 cognitively normal participants. The cohort was about equally divided between men and women, with a mean age of 79.2 years.

The Mayo team had participants’ olfactory function tested with a smell-identification kit. Typically these tests take minutes to administer and include common odorants like banana, gasoline, chocolate and soap.

All participants were imaged with MRI to ascertain cortical thickness and hippocampal volume. Several hundred were imaged with PET using the radiotracers 11C-PiB to assess amyloid accumulation and 18F-FDG to assess brain hypometabolism.

The researchers compared the biomarkers with the sniff-test results using multinomial logistic regression and linear regression models adjusted for potential confounders.

They found that reduced hippocampal volume, decreased Alzheimer’s signature cortical thickness and increased amyloid accumulation were significantly associated with increased odds of anosmia, the loss or impairment of the sense of smell.

Further, abnormal cortical thickness with Alzheimer’s signature and reduced hippocampal volume were associated with decreased olfactory identification as a continuous measure.

“Our findings suggest that odor identification may be a non-invasive, inexpensive marker for risk stratification, for identifying participants at the preclinical stage of Alzheimer’s disease who may be at risk for cognitive impairment and eligible for inclusion in Alzheimer’s prevention clinical trials,” the authors write.

The study was part of the population-based Mayo Clinic Study of Aging. Vassilaki and colleagues note that their cross-sectional findings connecting odor identification difficulties with Alzheimer’s neuroimaging biomarkers need to be validated prospectively.