Abstract
ObjectiveTo explore the value of olfactory identification deficits as a predictor of cerebral β-amyloid status and other markers of brain health in cognitively normal adults aged ~ 70 years.MethodsCross-sectional observational cohort study. 389 largely healthy and cognitively normal older adults were recruited from the MRC National Survey of Health and Development (1946 British Birth cohort) and investigated for olfactory identification deficits, as measured by the University of Pennsylvania Smell Identification Test. Outcome measures were imaging markers of brain health derived from 3 T MRI scanning (cortical thickness, entorhinal cortex thickness, white matter hyperintensity volumes); 18F florbetapir amyloid-PET scanning; and cognitive testing results. Participants were assessed at a single centre between March 2015 and January 2018.ResultsMean (± SD) age was 70.6 (± 0.7) years, 50.8% were female. 64.5% had hyposmia and 2.6% anosmia. Olfaction showed no association with β-amyloid status, hippocampal volume, entorhinal cortex thickness, AD signature cortical thickness, white matter hyperintensity volume, or cognition.Conclusion and relevanceIn the early 70s, olfactory function is not a reliable predictor of a range of imaging and cognitive measures of preclinical AD. Olfactory identification deficits are not likely to be a useful means of identifying asymptomatic amyloidosis. Further studies are required to assess if change in olfaction may be a proximity marker for the development of cognitive impairment.
Highlights
Simple, non-invasive markers of preclinical Alzheimer’s disease (AD) are needed
Extended author information available on the last page of the article individuals diagnosed with AD and mild cognitive impairment (MCI) have poorer Odour identification (OI), and OI deficits are associated with cognitive decline and conversion to MCI and AD [1]; and AD pathology affects olfactory pathways in older adults [2] and animal models [3]
We explored associations between OI and markers of cerebral β-amyloid deposition, neurodegeneration, and cognition in a uniquely well-characterised cohort of near identical age drawn from the MRC National Survey of Health and Development (NSHD; the British 1946 birth cohort)
Summary
Non-invasive markers of preclinical Alzheimer’s disease (AD) are needed. Odour identification (OI) deficits have been proposed as a potential risk marker for AD. Extended author information available on the last page of the article individuals diagnosed with AD and mild cognitive impairment (MCI) have poorer OI, and OI deficits are associated with cognitive decline and conversion to MCI and AD [1]; and AD pathology affects olfactory pathways in older adults [2] and animal models [3]. While the evidence for these associations in clinically defined groups is strong, the evidence regarding imaging biomarkers is more mixed. Considering the two largest cohorts, Vassilaki et al [4] and Growdon et al [5] each found associations between poorer OI and imaging markers of neurodegeneration.
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