Olfactory dysfunction as a marker of neurodegenerative disease in older adults

Early identification of neurodegenerative disorders in older adults remains a major challenge in geriatric clinical practice. Olfactory dysfunction is a common feature of several neurodegenerative disorders, particularly synucleinopathies, where it often precedes motor and cognitive symptoms, whereas in primary tauopathies olfactory function is usually preserved or only mildly impaired.

This study aimed to evaluate the diagnostic utility of the 12-item Sniffin' Sticks Test (SST-12) for identifying neurodegenerative disease in older adults.

A total of 120 individuals were included: 72 with synucleinopathies, 23 with tauopathies, and 25 healthy controls. Olfactory function was assessed using the SST-12. Group differences were analyzed using ANOVA, Fisher's exact test, and post hoc procedures. Diagnostic accuracy was evaluated by ROC analysis.

Anosmia occurred in 58.3% of synucleinopathy patients and 65.2% of tauopathy patients but was absent in controls (p < 0.0001). Women performed better on several items, while an age effect was observed only for odor T5 (banana) (p = 0.011). Subjective olfactory complaints had limited diagnostic value. The full SST-12 showed good accuracy in distinguishing patients from controls (AUC = 0.818; 95% CI 0.744-0.891). A shortened nine-odor version achieved slightly higher accuracy (AUC = 0.844; 95% CI 0.777-0.912). No significant difference was observed between synucleinopathies and tauopathies, including after adjustment for age and sex.

These findings support the clinical usefulness of brief olfactory testing in older adults and highlight the potential of selected odor subsets to improve screening efficiency.

The SST-12 is a sensitive and practical tool for detecting olfactory dysfunction in neurodegenerative disorders. Brief olfactory screening may represent a useful addition to routine geriatric assessment.