The first quick olfactory test specific for Alzheimer's disease and French culture

Abstract

Purpose: Olfactory identification disorder is considered a promising early biomarker of Alzheimer's disease (AD). The QUICK TODA2 can be used as a short olfactory screening tool specific for French AD patients. The selection of AD specific odorants and the design of this screening were the main objectives of this twofold study.

Methods: In study 1, the TODA2 olfactory test was administered to 43 mild-AD patients and 45 healthy controls (HC) in five memory centres in France. The selection of AD specific odorants was based on the differences in the proportion of correct answers and in the threshold means between AD and HC groups. In study 2, another set of 19 mild-AD patient were included at the memory centre of Nice Hospital. All participants completed the olfactory assessment pipeline including the QUICK TODA2, TODA2 and Sniffin' Sticks Identification sub-Test (SST-i). The individual scores of the three tests were correlated.

Results: In study 1, ten TODA2 odorants could significantly differentiate AD participants from controls. We selected the six most AD-sensitive items to design the QUICK TODA2. In study 2, we reported strong significant correlations between QUICK TODA2 and TODA2 (ρ₍₁₇₎ = 0.68, p = 0.001**), SST-i and QUICK TODA2 (ρ₍₁₇₎ = 0.65, p = 0.002**), SST-i and TODA2 (ρ₍₁₇₎ = 0.57, p = 0.01*).

Conclusion: QUICK TODA2 is a 5-min non-invasive olfactory AD screening tool dedicated to French culture. Its results converge with those of longer, validated olfactory tests. It could be used as a quick screening tool in the general daily practice before an extensive assessment in memory centres.

Keywords: Alzheimer’s disease; Cognitive impairment; Olfaction, olfactory test; Olfactory identification.