Odor Discrimination as a Marker of Early Alzheimer’s Disease

Abstract

Background: Olfactory dysfunction is an early symptom of Alzheimer’s disease (AD). However, olfactory tests are rarely performed in clinical practice because their diagnostic efficacy in detecting early AD is unclear. Objective: To investigate odor discrimination in patients with early AD and the efficacy of olfactory discrimination tests in differentiating these patients from subjects with normal cognition (CN). Methods: Thirty patients each with mild dementia due to AD (MD-AD) and mild cognitive impairment due to AD (MCI-AD) and 30 older subjects with CN were enrolled. All participants underwent cognitive examinations (CDR, MMSE, ADAS-Cog 13, and verbal fluency) and odor discrimination tests (Sniffin’ Sticks test, Burghart®, Germany). Results: The MD-AD group achieved significantly worse scores on the olfactory discrimination test than the MCI-AD group, and the MCI-AD group achieved significantly worse results than the CN group (p < 0.05). A cut-off score of≤10 had a diagnostic accuracy of 94.44% (95% CI, 87.51–98.17%) in differentiating patients with MCI-AD/MD-AD from subjects with CN and of 91.67% (95% CI, 81.61–97.24%) in differentiating those with MCI-AD from subjects with CN. Our multinomial logistic regression model with demographic data and ADAS-Cog 13 scores as predictor variables correctly classified 82.2% of the cases (CN, 93.3%; MC-AD, 70%; MD-AD, 83.3%); on adding the olfactory discrimination score to the model, the percentage increased to 92.2% (CN, 96.7%; MCI-AD, 86.7%; MD-AD, 93.3%). Conclusion: Odor discrimination is impaired in cases of early AD and continues to deteriorate as the disease progresses. The olfactory discrimination test showed good diagnostic efficacy in detecting early AD.

Approximation of Cognitive Performance Using an Elastic Net Regression Model Trained on Gait, Visual, Auditory, Postural, and Olfactory Function Features

“…The participants who were better at discerning which odors were different and which were the same performed better on the K-MoCA. Odor discrimination has been shown to be impaired in early cases of dementia and it deteriorates with the progression of the disease [25]. Additionally, a previous study concluded that odor discrimination is related to semantic memory and that noncognitive factors have only a minor influence on the score [47] therefore making the odor discrimination test a good measure of cognitive ability.…”

“…In the case of auditory ability, hearing loss was identified as a risk factor for dementia [19,20]. Alongside vision and hearing, sensory loss in olfaction is also considered a risk factor for developing dementia [21], and impaired olfaction was determined to have an association with cognitive decline and neurodegeneration in the brain [22,23], which is why some studies have attempted to detect dementia using olfactory function parameters [24][25][26].…”

Minding the Gap: Exploring Neuroinflammatory and Microglial Sex Differences in Alzheimer’s Disease

“…Female AD patients have greater brain atrophy and neurodegeneration than male AD patients, contributing to greater declines in memory, reasoning, language, and spatial orientation [2,7,10,35,[188][189][190][191]. As discussed extensively elsewhere [192][193][194][195], olfactory dysfunction has been reported in human AD patients and in mouse models of AD. It is one of the earliest clinical symptoms of AD, thereby acting as a biomarker of disease, and exhibits a strong sex bias.…”

Consensus on rapid screening for prodromal Alzheimer’s disease in China

“…Digital behavioural markers include physiological and behavioural information that is collected by digital techniques and quantifiable with clinical significance. 42 With the development of digital technology and medical artificial intelligence (AI), behavioural information such as eye movement, 43 44 olfactory identification, [45][46][47] natural speech, 41 48 49 driving 50 and gait features 51 are able to be detected via infrared, camera, recorder and wearable devices, contributing to the diagnosis and risk assessment of pAD (figure 1).…”