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BACKGROUND: Due to an ageing population and increased life expectancy, Alzheimer's dementia (AD) is becoming increasingly important. Since AD is characteristically preceded by subjective cognitive decline (SCD) and mild cognitive impairment (MCI), innovative diagnostic tools and therapeutics are essential for diagnosis at an early stage. Olfactory dysfunction is commonly associated with cognitive decline, indicating its potential as a diagnostic marker. OBJECTIVE: This study examined the association between olfactory function, evaluated with the Sniffin' Sticks Odor Identification Test (SS-OIT), and Assessment of Self-Reported Olfactory Functioning (ASOF) inventory across five cognitive subgroups (healthy controls HC, SCD, non-amnestic MCI, amnestic MCI, and AD). Furthermore, this study investigated the utility of olfactory testing in screening for AD. METHODS: This retrospective, single-center cross-sectional study was conducted at the Neurology Department of the Medical University of Vienna. The study included 958 participants during the period 2000-2023. Cognitive and olfactory functions were assessed using standardized neuropsychological and olfactory tools. Statistical analyses included descriptive measures, analysis of variance (ANOVA), model testing, and the receiver operating characteristic (ROC) methodology. RESULTS: Olfactory performance declined with increasing cognitive impairment, with the strongest contrast showing an effect size of r = 0.51 between HC and AD. The SS-OIT (area under the ROC curve AUC: 75.3%) and Olfactory-Related Quality of Life subscale (ORQ; AUC: 64.8%) were identified as the most effective in distinguishing AD, with the following recommended cut-offs: SS-OIT ≤ 9; Subjective Olfactory Capability (SOC) ≤ 6; Self-Reported Capability of Perceiving Specific Odors (SRP) ≤ 4.10; and ORQ ≤ 3.67. CONCLUSION: Olfactory functioning shows moderate reliability in distinguishing subgroups; nevertheless, the proposed cut-off values may be suitable for AD screening. Further studies are recommended to confirm our findings.
Dopke et al. (Fri,) studied this question.