Expanding the scope of olfactory evaluation in Alzheimer's disease and related dementias (ADRD): A narrative review of the role for odor memory and recognition in AD/ADRD

Abstract

Olfactory dysfunction (OD) is a well-characterized feature of Alzheimer's disease (AD) and is often one of the earliest functional biomarkers in the disease course. As such, olfactory evaluation shows promise as an important tool in AD screening and may provide insight into pathologic underpinnings and potential treatment pathways. The National Plan to Address Alzheimer's Disease emphasizes the importance of including Alzheimer's disease related dementias (ADRD) in research efforts, and while olfaction is also associated with ADRD, this association is relatively understudied. Additionally, there have been efforts to expand the evaluation of olfactory function to include assessments beyond key domains, such as odor threshold, odor discrimination, and odor identification, which have been the primary focus of most olfaction research in AD/ADRD. Odor recognition memory assessments have been developed primarily for their utility in identifying and stratifying individuals along the AD continuum, although a wide variety of methods have been reported in the literature. In this narrative review, we provide an overview of odor identification, odor threshold, and odor discrimination in AD/ADRD with a specific focus on providing a centralized guide detailing odor recognition memory methods and their utility in AD/ADRD.

Keywords: Alzheimer's disease; Lewy body disease; dementia; frontotemporal dementia; memory and learning; olfaction; vascular dementia.