Olfactory identification disorders due to Alzheimer’s disease: A new test from France to Quebec

Abstract

Olfactory identification disorder is regarded as an early marker of Alzheimer’s disease (AD) and of similar diagnostic significance of biological or cognitive markers. Premature damage of the entorhinal olfactory cortex, the hippocampus and the orbitofrontal cortex characterize AD and suggest a specific impairment of olfactory identification. The use of psychophysical olfactory identification tests in clinical diagnostic practice is therefore strongly recommended, but not required. As these widespread tests are rarely used, an innovative test, adapted to this target group has been developed. It has been used and validated in a routine care protocol at different Memory Centers in France and in Quebec, Canada. A total of 157 participants were recruited: including 63 Alzheimer’s patients and 94 healthy controls. The test was composed of 14 odorants diluted into 4 different concentrations. A computer interface generated randomization of 6 odors per participant and the automatic calculation of identification scores, of perceptual thresholds and of composite scores. All participants underwent a Mini Mental Scale Examination within the previous three months or on the same day of the olfactory test. The Alzheimer’s patients had a score between 20 and 30 and healthy controls participants had a score above 28 without any loss of points on recalled items. The results show that our olfactory identification test is able to significantly differentiate Alzheimer’s patients from healthy controls (p < 0.001), and to distinguish the French population tested from the Quebec population (p < 0.001). This study highlights an olfactory identification disorder as a target for early diagnosis of AD. Its cultural qualities make it a potential candidate for differentiated calibration between France and Quebec.

Correlations between Persistent Olfactory and Semantic Memory Disorders after SARS-CoV-2 Infection

“…This disease particularly affects odor identification at an early stage, whereas threshold and discrimination are preserved in the early stages of the disease, revealing an impairment of the olfactory semantic memory. This is due to alterations in the entorhinal cortex, hippocampus, and orbitofrontal cortex, which are also regions that manage semantic memory [ 55 ]. Therefore, this test contains semantically related items highlighting mild semantic impairment more easily.…”

“…Olfactory function was assessed using two tests: Sniffin’ Sticks Test (SST) [ 53 , 54 ] and Test Olfactif informatisé pour le Diagnostic de la maladie d’Alzheimer et de l’Apathie (TODA patent application filed on 28 September 2021) [ 55 ].…”

“…Olfaction evaluation was completed with the TODA test, developed by Côte d’Azur University and Nice University Hospital, and included a 14 fragrances kit and an application recording the test and results [ 55 ]. These 14 odorants were in compact jars filled with paraffin wax.…”

Perceptual odor qualities predict successful odor identification in old age

“…Future research may address whether these different clinical groups might be impaired on different perceptual odor features. If this hypothesis is confirmed in future research, odor intensity, pleasantness, and edibility could be considered when selecting odors for rapid identification tests aimed at differentiating between, for example, healthy older adults and those with an increased risk of developing dementia ( Payne et al 2022 ). Understanding which odors are most identifiable in older adults can also be useful in developing consumer products for older consumers.…”

A Perspective: Challenges in Dementia Research

“…Other important non-neuropsychological clinical tests that can provide insight into dementia involve eye movements [ 24 , 25 ], retinal function [ 26 ], gait [ 27 ], olfaction [ 28 , 29 ], taste [ 30 ] and hand movements [ 31 ].…”