Association of odor identification capacity with amyloid‐β and tau burden in older adults: A systematic review and meta‐analysis

Abstract

AbstractBackgroundPrevious studies have shown that smell identification test might predict cognitive decline in older adults. However, whether the odor identification capacity correlates to the pathological change of Alzheimer’s disease (AD) has not been fully investigated. The systematic review aimed to examine the association between odor identification capacity and the amyloid‐β (Aβ) and tau burden in older adults.MethodElectronic databases (MEDLINE, PsycINFO, Google Scholar) were searched up to June 2019 to identify studies that reported the correlation coefficients or regression coefficients between odor identification test scores and Aβ or tau levels in cerebrospinal fluid (CSF) or Aβ burden detected by 11C‐Pittsburgh compound B (PiB) positron emission tomography (PET). The protocol was pre‐specified (PROSPERO CRD42019138642).Result660 abstracts were retrieved, and 30 full‐text articles further explored, from which 24 were excluded. In the final sample, we identified four studies (468 participants) regarding Aβ PiB PET and two studies (223 participants) about Aβ or tau levels in CSF. There was a significant inverse linear relationship between odor identification test scores and global PiB binding (pooled correlation coefficient = ‐0.35, 95% confidence interval (CI)= ‐0.54∼‐0.13, p=0.002). There was no significant association between CSF Aβ1‐42 levels and odor identification test score (pooled correlation coefficient = 0.22, 95% CI= ‐0.04∼0.45, p=0.097). Due to lack of data, no pooled correlation coefficients could be computed on the association between odor identification test score and CSF tau level or the ratio of the Aβ1‐42 and tau.ConclusionThere was an inverse association between odor identification capacity and global cerebral Aβ burden in older adults. It suggests that odor identification capacity might be a proxy marker of preclinical Alzheimer’s disease.