Severe Dysosmia Is Specifically Associated with Alzheimer-Like Memory Deficits in Nondemented Elderly Retirees

Abstract

To determine whether or not (1) impaired olfactory function is associated with impaired memory on neuropsychological testing in healthy retirees, and if so then (2) whether memory impairment is most consistent with a mesiotemporal rather than frontal system disorder. 173 independent residents of a continuing care retirement community were studied. Subjects completed the University of Pennsylvania Smell Identification Test (UPSIT) and a battery of both general and specific cognitive measures that included the Mini-Mental State Examination (MMSE) and the Executive Interview (EXIT25). Subjects were examined twice over 3 years. UPSIT performance was normal in 21% and in the 'anosmic' range in 25% of subjects. Anosmic UPSIT performance was associated with significantly worse performance on all cognitive tests. However, only short-term verbal memory was independently associated with UPSIT-defined anosmia. This association remained significant after adjusting for the other cognitive and sociodemographic variables. The memory deficits of anosmic subjects were qualitatively consistent with a cortical type (type 1) dementing illness such as Alzheimer's disease (AD). Over time, UPSIT-defined 'anosmic' cases suffered significantly greater declines on both the MMSE and the EXIT25, independently of baseline age, gender and MMSE score. Impaired odor identification in individuals without overt dementia is associated with an AD-like memory impairment and an increased rate of cognitive decline. The comorbid association of these deficits is consistent with the known hierarchical spread of preclinical AD pathology and may be a specific indicator of future clinical AD dementia.