Olfaction, Cognitive Impairment, and PET Biomarkers in Community-Dwelling Older Adults

Background: Olfactory deficits are early features of preclinical Alzheimer's disease (AD). Whether olfaction is associated with PET biomarkers among community-dwelling older adults is less clear. Objective: Investigate cross-sectional and longitudinal associations of olfaction with mild cognitive impairment (MCI) and amyloid-beta (A beta) and tau deposition. Methods: We analyzed 364 initially cognitively normal participants (58% women, 24% black) who had baseline olfaction data and subsequent cognitive assessments during an average 2.4-year. A subset of 129 had PET-PiB (A beta) (n = 72 repeated) and 105 had 18F-flortaucipir (FTP)-PET (tau) (n = 44 repeated). Olfaction was measured using a 16-item Sniffin' Sticks Odor Identification Test. The association of olfaction with incident MCI was examined using Cox regression. Associations with PiB-distribution volume ratio (DVR) and FTP-standardized uptake value ratio (SUVR) were examined using partial correlation. We tested whether PiB+/- status modified these associations. Analyses were adjusted for demographics and olfactory test version. Results: 17 (5%) participants developed MCI. Each unit lower odor identification score was associated with 22% higher risk of developing MCI (p = 0.04). In the PET subset, lower scores were associated with higher mean cortical DVR and DVR in orbitofrontal cortex (OFC), precuneus, and middle temporal gyrus (p <= 0.04). The olfaction*PiB+/- interaction in OFC DVR was significant (p = 0.03), indicating the association was limited to PiB positive individuals. Greater decline in odor identification score was associated with greater increase in anterior OFC DVR and entorhinal tau SUVR (p= 0.03). Conclusion: Among community-dwelling older adults, poorer olfaction predicts incident MCI and is associated with overall and regional A beta. Greater olfaction decline is associated with faster A beta and tau accumulation in olfaction-related regions. Whether olfaction predicts AD-related neurodegenerative changes warrants further investigations.

Automated summary

Olfactory deficits are associated with mild cognitive impairment, amyloid-beta, and tau deposition among community-dwelling older adults. Poorer olfaction predicts incident MCI, and greater olfaction decline is linked to faster accumulation of A beta and tau in specific brain regions. Further investigations are needed to determine if olfaction can predict AD-related neurodegenerative changes.