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A Free-breathing fMRI Method to Study Human Olfactory Function

A Free-breathing fMRI Method to Study Human Olfactory Function

Published on: July 30, 2017

Single odor identification in subjective cognitive decline, mild cognitive impairment and Alzheimer's dementia

Abdallah Tasnim¹, Johann Lehrner²

¹Department of Neurology, Medical University of Vienna, Währinger Gürtel 18-20, 1090, Vienna, Austria.

Wiener Klinische Wochenschrift

|March 9, 2026

Abstract

Background:

Olfactory dysfunction is an early biomarker of Alzheimer's dementia (AD) and cognitive impairments. This study examines odor-specific olfactory deficits across cognitive impairment stages using the Sniffin' Sticks Odor Identification Test (SS-OIT).

Objective:

To assess the discriminative validity of specific odors in differentiating subjective cognitive decline (SCD), non-amnestic mild cognitive impairment (naMCI), amnestic mild cognitive impairment (aMCI), and AD from healthy controls (HC). Additionally, the influences of age, gender, verbal intelligence and depression on olfactory performance were analyzed. Participants were also grouped into an AD versus non-AD category (comprising SCD, naMCI, and aMCI) for logistic regression analyses.

Methods:

A retrospective analysis at the Department of Neurology of the Medical University of Vienna included 737 participants aged 50 years and older. Olfactory identification was assessed using the 16-item Sniffin' Sticks odor identification test. The discriminative power of specific odors was evaluated for distinguishing AD from non-AD groups. Bonferroni corrections were applied to adjust for multiple comparisons, which increases the stringency of statistical significance across the 16 odors tested.

Results:

Significant differences in odor identification were observed across diagnostic groups. The AD patients exhibited the most pronounced deficits, particularly in recognizing clove, rose and aniseed. Age negatively correlated with olfactory performance, while higher verbal intelligence was a protective factor. Key odors differentiated AD from non-AD groups, highlighting the diagnostic potential of olfactory testing.

Conclusion:

Odor-specific olfactory deficits serve as early indicators of cognitive decline. The Sniffin' Sticks test, particularly key odors, may aid early detection and differentiation of cognitive impairments. Accounting for covariates enhances the diagnostic accuracy. Future research should aim to refine olfactory testing protocols and assess their clinical utility in broader populations.

Keywords:

Early diagnosis Elderly Item-specific analysis Smell disorder

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