Predictive value of olfactory impairment for cognitive decline among cognitively normal adults

Objective: Dementia affects over 47 million people worldwide. Olfactory impairment (OI) is a well-established predictive marker of conversion to dementia among those with mild cognitive impairment. This systematic review aims to describe the predictive value of OI for future cognitive decline among cognitively normal adults. Methods: A literature search encompassing PubMed, EMBASE, and Cochrane for longitudinal cohort studies following cognitively normal adults with baseline OI in comparison to those without OI reporting incident cognitive impairment or dementia was included. Study design, participant demographics, olfactory testing method, and incidence of cognitive decline or dementia were abstracted. Two investigators independently reviewed all articles. Results: The search yielded 964 nonduplicate abstracts and titles, from which 19 full-text articles were reviewed and 10 were included. Studies included were all good quality (mean score 8.7 of 9), and all studies (100%) found a statistically significant association between baseline OI and incident cognitive decline compared with normosmic controls. Conclusion: The existing literature suggests that OI predicts future cognitive decline among cognitively normal adults, supporting olfactory evaluation as a low-cost, minimally invasive, and widely available screening tool to be used in combination with other tests to identify adults at early risk of dementia. Level of Evidence: NA Laryngoscope, 130:840–847, 2020.