Trajectories of olfactory identification preceding incident mild cognitive impairment and dementia: a longitudinal study.
Level 3 - non-randomized controlled study
Prospective longitudinal cohort study with postmortem pathology
PubMed 38251465 · doi:10.1016/j.ebiom.2023.104862
What was done
Within the Rush Memory and Aging Project, 1,318 dementia-free older adults were followed annually for up to 11 years. Olfactory identification was evaluated annually using the Brief Smell Identification Test. Incident mild cognitive impairment (MCI) and dementia diagnoses were tracked in 900 cognitively intact participants. Neuropathological assessments were performed on brain autopsies from 518 participants who died during follow-up. Trajectories were analyzed using mixed-effect models with backward timescales.
What was found
Participants developing MCI had faster olfactory identification decline than those remaining cognitively intact (β = -0.09 [95% CI -0.13, -0.05]), showing significantly lower performance starting 5 years before MCI diagnosis (mean difference at year -5: -0.39 [-0.71, -0.07]). Among participants with incident MCI, those progressing to dementia declined faster than non-progressors (β = -0.19 [-0.36, -0.01]), showing significantly lower scores starting 3 years prior to dementia diagnosis (mean difference at year -3: -0.95 [-1.67, -0.23]). Faster olfactory decline correlated with higher global Alzheimer's pathology, neurofibrillary tangles, and amyloid-beta load.
Why it matters
Accelerated decline in olfactory identification serves as an early behavioral marker appearing years before clinical MCI and dementia diagnoses, linked directly to accumulating Alzheimer's pathology.
Limits
The abstract lacks demographic details (e.g., age, sex, race) and information on whether analyses adjusted for potential confounders such as smoking or sinonasal disease. Autopsy data were limited to participants who died during the follow-up period.
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