Olfactory evaluation in Mild Cognitive Impairment: correlation with neurocognitive performance and endothelial function

The role of olfactory dysfunction in mild cognitive impairment and Alzheimer's disease: A meta-analysis

PURPOSE

This comprehensive meta-analysis investigates the association between olfactory deficits in mild cognitive impairment (MCI) and Alzheimer's disease (AD).

METHODS

A thorough search across databases identified articles analyzing olfactory status in MCI or AD patients. Methodological quality assessment followed PRISMA guidelines. Hedges' g effect size statistic computed standard mean differences and 95% confidence intervals. Moderator analysis was conducted.

RESULTS

Among the included studies (65 for MCI and 61 for AD), odor identification exhibited larger effect sizes compared to odor threshold and discrimination, in both MCI and AD samples. Moderate effect size is found in OI scores in MCI (k = 65, SE = 0.078, CI 95% = [-1.151, -0.844]). Furthermore, compared to MCI, AD had moderate to large heterogeneous effects in olfactory identification (k = 61, g = -2.062, SE = 0.125, CI 95% = [-2.308, -1.816]). Global cognitive status is positively related to olfactory identification impairment in both MCI (k = 57, Z = 2.74, p = 0.006) and AD (k = 53, Z = 5.03, p < 0.0001) samples.

CONCLUSION

Olfactory impairments exhibit a notable and substantial presence in MCI. Among these impairments, odor identification experiences the greatest decline in MCI, mirroring the primary sensory deficit observed in AD. Consequently, the incorporation of a straightforward odor identification test is advisable in the evaluation of individuals vulnerable to the onset of AD, offering a practical screening tool for early detection.

Social odor choice buffers drug craving

Social interactions are rewarding and protective against substance use disorders, but it is unclear which specific aspect of the complex sensory social experience drives these effects. Here, we investigated the role of olfactory sensory experience on social interaction, social preference over cocaine, and cocaine craving in rats. First, we conducted bulbectomy on both male and female rats to evaluate the necessity of olfactory system experience on the acquisition and maintenance of volitional social interaction. Next, we assessed the effect of bulbectomy on rats given a choice between social interaction and cocaine. Finally, we evaluated the influence of olfactory sensory experience by training rats on volitional partner-associated odors, assessing their preference for partner odors over cocaine to achieve voluntary abstinence and assessing its effect on the incubation of cocaine craving. Bulbectomy impaired operant social interaction without affecting food and cocaine self-administration. Rats with intact olfactory systems preferred social interaction over cocaine, while rats with impaired olfactory sense showed a preference for cocaine. Providing access to a partner odor in a choice procedure led to cocaine abstinence, preventing incubation of cocaine craving, in contrast to forced abstinence or non-contingent exposure to cocaine and partner odors. Our data suggests the olfactory sensory experience is necessary and sufficient for volitional social reward. Furthermore, the active preference for partner odors over cocaine buffers drug craving. Based on these findings, translational research should explore the use of social sensory-based treatments utilizing odor-focused foundations for individuals with substance use disorders.

Valid olfactory impairment tests can help identify mild cognitive impairment: an updated meta-analysis

Background

Olfactory testing is emerging as a potentially effective screening method for identifying mild cognitive impairment in the elderly population.

Objective

Olfactory impairment is comorbid with mild cognitive impairment (MCI) in older adults but is not well-documented in subdomains of either olfactory or subtypes of cognitive impairments in older adults. This meta-analysis was aimed at synthesizing the differentiated relationships with updated studies.

Methods

A systematic search was conducted in seven databases from their availability to April 2023. A total of 38 publications were included, including 3,828 MCI patients and 8,160 healthy older adults. Two investigators independently performed the literature review, quality assessment, and data extraction. The meta-analyses were conducted with Stata to estimate the average effects and causes of the heterogeneity.

Results

Compared to normal adults, MCI patients had severe impairments in olfactory function and severe deficits in specific domains of odor identification and discrimination. Olfactory impairment was more severe in patients with amnestic mild cognitive impairment than in patients with non-amnestic MCI. Diverse test instruments of olfactory function caused large heterogeneity in effect sizes.

Conclusion

Valid olfactory tests can be complementary tools for accurate screening of MCI in older adults.

Olfactory Dysfunction Associated with Cognitive Decline in an Elderly Population

BACKGROUND

In many neurological disorders, including Alzheimer disease, early olfactory dysfunction is observed.

OBJECTIVE

In order to determine if deficits in olfactory memory are present in the elderly and if olfactory dysfunction correlates with cognitive impairment in the aging population, olfactory testing has been done on seniors from the NuAge cohort accepting to participate in the Olfactory Response Cognition and Aging (ORCA) secondary sub-study. The t-Mini Mental Statement Examination and the Telephone Interview for Cognitive Status tests were done to assess cognition levels.

RESULTS

Overall, 94% of the ORCA cohort displayed olfactory dysfunction. Deficits in olfactory memory were also present. A correlation was observed between olfactory function and cognitive test scores. Moreover, in women who smoked, there was an association between olfactory memory and cognitive scores.

CONCLUSION

Our results suggest that olfactory dysfunction may predict impending cognitive decline and highlights the need for olfactory training in seniors to improve olfaction and overall well-being.

Smaller grey matter volume in the central olfactory system in mild cognitive impairment

One of the major challenges in the diagnosis of Alzheimer's disease (AD) is to increase the specificity of the early diagnosis. While episodic memory impairment is a sensitive AD marker, other measures are needed to improve diagnostic specificity. A promising biomarker might be a cerebral atrophy of the central olfactory processing areas in the early stages of the disease since an impairment of olfactory identification is present at the clinical stage of AD. Our goal was therefore, (1) to evaluate the grey matter volume (GMV) of central olfactory processing regions in prodromal AD and (2) to assess its association with episodic memory. We included 34 cognitively normal healthy controls (HC), 92 individuals with subjective cognitive decline (SCD), and 40 with mild cognitive impairment (MCI). We performed regions of interest analysis (ROI) using two different approaches, allowing to extract GMV from (1) atlas-based anatomical ROIs and from (2) functional and non-functional subregions of these ROIs (olfactory ROIs and non-olfactory ROIs). Participants with MCI exhibited smaller olfactory ROIs GMV, including significant reductions in the piriform cortex, amygdala, entorhinal cortex, and left hippocampus compared to other groups (p ≤ 0.05, corrected). No significant effect was found regarding anatomical or non-olfactory ROIs GMV. The left hippocampus olfactory ROI GMV was correlated with episodic memory performance (p < 0.05 corrected). Limbic/medial-temporal olfactory processing areas are specifically atrophied at the MCI stage, and the degree of atrophy might predict cognitive decline in AD early stages.

Olfactory function reflects episodic memory performance and atrophy in the medial temporal lobe in individuals at risk for Alzheimer's disease

We examined cognitive domains and brain regions associated with olfactory performance in cognitively unimpaired older adults (CU-OAs) and individuals with or at risk for Alzheimer's Disease (AD). We compared CU-OAs (N = 55), individuals with subjective cognitive decline (SCD, N = 55), mild cognitive impairment (MCI, N = 101), and AD (N = 45) on measures of olfactory function (Brief Smell Identification Test), cognition (episodic and semantic memory), and medial temporal lobe thickness and volume. Analyses controlled for age, sex, education, and total intracranial volume. Olfactory function decreased from SCD to MCI to AD. CU-OAs outperformed all groups except SCDs on tests of cognition and olfaction. Although these measures did not differ between the CU-OAs and SCDs, olfactory function correlated with episodic memory tests and with entorhinal cortex atrophy only in the SCD group. Olfactory function also correlated with hippocampal volume and right-hemisphere entorhinal cortex thickness in the MCI group. Olfactory dysfunction reflects medial temporal lobe integrity and memory performance in a group at risk for AD with normal cognition and olfaction.

Specific olfactory deficit patterns observed in seniors and associated with cognitive decline

Olfactory dysfunction is a common symptom in neurodegenerative disorders and is regarded as a potential early predictor of impending cognitive decline. This study was undertaken in order to determine if olfactory dysfunction observed in the elderly is due to a general loss of smell or the inability to detect specific odours, and if misidentification of odours correlates with cognitive scores. Seniors for the Olfactory Response and Cognition in Aging (ORCA) sub-study were recruited from the Quebec Nutrition and Successful Aging (NuAge) cohort. The University of Pennsylvania smell identification test (UPSIT) was performed to measure olfactory function and the telephone Mini Mental State Examination (t-MMSE) and the French version of the Telephone Interview for Cognitive Status Modified (F-TICS-m) for cognitive status. The results demonstrate that seniors exhibit specific olfactory loss and had severe difficulty in particular in identifying lemon, pizza, fruit punch, cheddar cheese and lime. Furthermore, there was a significant difference in the ability to detect certain odours between the sexes. Results also showed that misidentification of certain scents was associated with cognitive scores, and when the sexes were assessed separately sex-specific misidentification of cognitive-associated odours was observed. The relationship between the cognitive scores and scent misidentification suggests that impending cognitive decline may be highlighted by the inability to smell specific odours. Our study provides additional support for the testing of olfactory function in the elderly and suggests that loss of smell for particular scents may become a useful diagnostic tool.

Olfaction and declarative memory in aging: a meta-analysis

Olfactory and declarative memory performances are associated, as both functions are processed by overlapping medial-temporal and prefrontal structures and decline in older adults. While a decline in olfactory identification may be related to a decline in declarative memory, the relationship between olfactory detection threshold and declarative memory remains unclear. In this meta-analysis, we assessed (i) the relationship between olfactory identification/detection threshold and verbal declarative memory in cognitively normal older adults, and (ii) the effect of age on these relationships. We included articles from PsychNet, PubMed, and Academic Search Complete according to the following criteria: (i) inclusion of cognitively normal older adults; (ii) assessment of episodic or semantic memory; and (iii) assessment of olfactory identification or detection threshold. Seventeen studies and 22 effect sizes were eligible and included in this meta-analysis. Olfactory identification was associated with episodic (small effect size: r = 0.19; k = 22) and semantic memory (small effect size: r = 0.16; k = 23). Similarly, the olfactory detection threshold was associated with both episodic (small to medium effect size: r = 0.25; k = 5) and semantic memory (small effect size: r = 0.17; k = 7). Age was found to moderate the relationship between olfactory detection threshold and memory performance. Both olfactory identification and detection threshold performances are associated with declarative memory in older adults, and age only moderates the relationship between olfactory detection threshold and declarative memory performances.

Olfactory discrimination and identification as prognostic markers of fitness-to-drive in older drivers

The necessity for reliable, standardized and validated fitness to drive assessment tools for older drivers have been highlighted and discussed for over three decades. Existing neuropsychological tests of driving performance are focusing mostly on visuo-spatial attention and executive functioning rather than other senses. Over the last decade, olfactory deterioration has been found to be associated with cognitive decline and predicting transition from mild cognitive impairment to dementia. The AGILE fitness to drive battery is standardized for older drivers. In this study it was adapted to include the olfactory Sniff' and Stick's test. The aim was to investigate the value of relevant deficits as predictive markers of driving ability in three driving groups (older drivers with: (a) no impairment (controls), (b) with Mild Cognitive Impairment (MCI) and (c) MCI and other chronic conditions, i.e., comorbidities). So far, no other study has investigated the predictive value of olfactory deficits in driving ability. The findings revealed that discrimination is important for the first year of the examination and as the decline progresses, identification becomes the better olfactory marker. The latter is also evident in the literature. Hence, the results showed that less indicators are required compared to the initial battery. The olfactory markers were dominant over the neuropsychological tests, apart from alertness, for predicting the older driver's fitness to drive regardless of the presence of cognitive impairment and other chronic conditions.

Olfactory dysfunction is associated with mild cognitive impairment in community-dwelling older adults

Background

Olfactory impairment is aging related and is associated with cognitive decline in older adults. However, it remains unclear if an olfactory impairment is associated with mild cognitive impairment (MCI) and the degree of impairment in the MCI subtypes.

Materials and methods

In a cohort of community-living older adults aged 60 years and above, 670 participants were recruited from the Community Health and Intergenerational (CHI) Study. Olfactory function was assessed using a locally developed nine-item smell test in association with neurocognitive assessments. Analysis of covariance (ANCOVA) was used to examine the association of smell identification score and clinical cognitive status while considering demographic, clinical, and neuropsychological factors with Bonferroni correction for group comparisons.

Results

Age-related smell detection between normal aging (NA) and MCI participants had no significant difference. The overall mean smell identification score in older adults was negatively correlated with age. The mean smell identification score of MCI participants was also not significantly different as compared with NA, but an amnestic MCI multiple domain (aMCI_MD) subgroup had significantly lower (impaired) mean smell identification scores compared with the NA and MCI single domain (amnestic and non-amnestic) group.

Conclusion

This study demonstrated that olfactory identification impairment is a comorbidity in older adults with amnestic MCI (aMCI) and is a potential marker associated with an early stage of a neurocognitive disorder. The smell test could act as a screening tool to help in the early detection of smell impairment for heterogeneous syndromes of MCI among community-dwelling older adults. Clinicians and researchers could benefit from utilizing the locally developed smell test to screen their patients or research participants before the initiation of an appropriate health intervention or in a clinical trial.

Healthy aging: the INTECMAN project

Aging is associated not only with the reduction of psychophysical and sensory capacities but also with different types of neurodegenerative disorders up to dementia manifestations. Aging in health and self-sufficiency is strictly dependent on the prevention and correction of factors that may determine reduction of psychophysical capacities (e.g., cardiovascular, locomotor and neurodegenerative ones). To reach this goal, due to the dynamics of social and family changes and to the aging of the population, health professionals can be supported by technologies which provide noninvasive monitoring of physiologic parameters and rely on telemedicine, both instruments of support and care for better aging in the home setting. The authors, starting from the initial idea of a personalized monitoring of different psychophysical variables, defined a pilot study to assess the role of a 12-month individually tailored lifestyle counseling on parameters of mild cognitive impairment in a group of elderly subjects. Data derived from the applied approach appeared promising and may open the road to the possible implementation of individual counseling, based on multiparametric non-obtrusive technologies which take into consideration both psychological and physical aspects, to be followed in the home environment.

Odor Sensitivity Versus Odor Identification in Older US Adults: Associations With Cognition, Age, Gender, and Race

The ability to identify odors predicts morbidity, mortality, and quality of life. It varies by age, gender, and race and is used in the vast majority of survey and clinical literature. However, odor identification relies heavily on cognition. Other facets of olfaction, such as odor sensitivity, have a smaller cognitive component. Whether odor sensitivity also varies by these factors has not been definitively answered. We analyzed data from the National Social Life, Health, and Aging Project, a nationally representative study of older US adults (n = 2081). Odor identification was measured using 5 validated odors presented with Sniffin' Stick pens as was odor sensitivity in a 6-dilution n-butanol constant stimuli detection test. Multivariate ordinal logistic regression modeled relationships between olfaction and age, gender, race, cognition, education, socioeconomic status, social network characteristics, and physical and mental health. Odor sensitivity was worse in older adults (P < 0.01), without gender (P = 0.56) or race (P = 0.79) differences. Odor identification was also worse in older adults, particularly men (both P ≤ 0.01), without differences by race. Decreased cognitive function was associated with worse odor identification (P ≤ 0.01) but this relationship was weaker for odor sensitivity (P = 0.02) in analyses that adjusted for other covariates. Odor sensitivity was less strongly correlated with cognitive ability than odor identification, confirming that it may be a more specific measure of peripheral olfactory processing. Investigators interested in associations between olfaction and health should consider both odor sensitivity and identification when attempting to understand underlying neurosensory mechanisms.

Vitamin D and Folate as Predictors of MMSE in Alzheimer's Disease: A Machine Learning Analysis

Vitamin D (VD) and micronutrients, including folic acid, are able to modulate both the innate and the adaptive immune responses. Low VD and folic acid levels appear to promote cognitive decline as in Alzheimer’s disease (AD). A machine learning approach was applied to analyze the impact of various compounds, drawn from the blood of AD patients, including VD and folic acid levels, on the Mini-Mental State Exam (MMSE) in a cohort of 108 patients with AD. The first analysis was aimed at predicting the MMSE at recruitment, whereas a second investigation sought to predict the MMSE after a 4 year follow-up. The simultaneous presence of low levels of VD and folic acid allow to predict MMSE, suggestive of poorer cognitive function. Such results suggest that the low levels of VD and folic acid could be associated with more severe cases of cognitive impairment in AD. It could be hypothesized that simultaneous supplementation of VD and folic acid could slow down the progression of cerebral degeneration at least in a subset of AD individuals.

The Association between Olfactory Function and Cognitive Impairment in Older Persons with Cognitive Impairments: A Cross-Sectional Study

Olfactory function is an emerging topic of research in the fields of cognitive impairment and neurodegenerative diseases. We aimed to confirm the association between olfactory function and cognitive impairment by assessing the olfactory function of older persons with cognitive impairment and identify whether olfactory function is associated with cognitive impairment. For this study, we recruited 117 older people aged ≥65 years with cognitive impairments from a public hospital in Korea. We used the Korean version of the expanded clinical dementia rating scale to evaluate participants’ cognitive impairments, and the University of Pennsylvania’s smell identification test to assess their olfactory function. Our results indicate a significant negative correlation between olfactory function and all domains of cognitive impairment (memory, orientation, judgement and problem-solving, community affairs, home and hobbies, and personal care). In addition, olfactory function was a factor associated with cognitive impairment in older persons. Therefore, we expect that our results to provide useful data for the development of interventions using olfactory stimulation to improve cognitive function in older persons with cognitive impairment.

Narrative Review of Sensory Changes as a Biomarker for Alzheimer's Disease

Early recognition of Alzheimer's disease (AD) in the prodromal period has not been robust yet will be necessary if effective disease-modifying drugs are to be useful in preventing or delaying the condition. The objective of this narrative review was to describe the current, evidenced based understanding of alterations in sensory data as potential biomarkers for AD. Review of empirical studies that tested senses as biomarkers for AD and were published in English within the past 50 years was completed. Eighteen empirical studies were identified that met the strict criteria for inclusion, with 12 of these studies being related to the olfactory system. Two studies examined auditory, two examined vision, one examined proprioception, and one examined taste. Thus, only olfaction has been studied to any extent, leaving a clear gap in the literature for the use of other senses. A promising area of research has begun to be reported concerning differences in responses to pain stimuli in AD relative to cognitively normal subjects. Pain is not a single sense like the others but integrates several senses and may allow for use as an early biomarker for AD, as it integrates several brain areas and pathways. Unlike the other senses, simple devices can be used to measure changes in pain perception in cognitively normal adults with genetic predispositions for possible AD, making this potentially useful for clinicians in the future.

IL33/ST2 Axis in Diabetic Kidney Disease: A Literature Review

Interleukin-33 (IL-33) is a cytokine belonging to the IL-1 family, playing a role in inflammatory, infectious and autoimmune diseases and expressed in the cellular nucleus in several tissues. High levels of IL-33 are expressed in epithelial barrier tissues and endothelial barriers. ST2 is a receptor for IL-33, expressed selectively on a subset of Th2 cells, mediating some of their functions. The IL-33/ST2 axis plays an important role in several acute and chronic inflammatory diseases, including asthma and rheumatoid arthritis. Different disorders are related to the activity of IL-33, ST2, or their axis, including cardiovascular disease or renal disturbances. Therefore, in the present work, a literature review was conducted, covering the period from 1 January 2000 to 30 November 2018, in PubMed, ScienceDirect, and Google Scholar database, to assess the involvement of the IL-33/ST2 axis in diabetic kidney disease. 6 articles directly dealing with the argument were identified, highlighting a clear link between IL-33/ST2 axis and diabetic kidney disease or related nephropathy. Overall, the involvement of ST2 seems to be more predictive than IL-33, especially in investigating the deterioration of kidney function; however, both compounds are pivotal in the field of renal diseases. Future studies are required to confirm the scientific evidences on larger and more heterogeneous cohorts.

Association Between Olfactory and Gustatory Dysfunction and Cognition in Older Adults

Background

The association between olfactory dysfunction (OD) and cognitive decline is becoming apparent in the emerging literature. However, the literature demonstrating a similar effect between gustatory dysfunction (GD) and cognition is not well established.

Objective

To determine whether OD and GD are independently associated with cognitive impairment.

Methods

The 2013–2014 National Health and Nutrition Examination Survey was queried for 1376 older adults, corresponding to a weighted population sample of 50 816 529, to assess olfactory and gustatory status and cognition using univariate and multivariate regression analyses. OD and GD were determined using objective measurements with validated protocols. Participants were stratified as normal or abnormal cognition status using accepted cutoff values as indicated for the Consortium to Establish a Registry for Alzheimer’s Disease (CERAD) neuropsychological test, Animal Fluency Test (AFT), and Digit Symbol Substitution Test (DSST).

Results

OD was associated with both mild cognitive impairment (odds ratio [OR] 1.809, P = .004) and dementia (OR 3.173, P < .001) with CERAD testing, abnormal AFT (OR 2.424, P < .001), and abnormal DSST (OR 4.028, P < .001). GD based on 1M NaCl whole mouth taste testing was associated with dementia on CERAD testing (OR 2.217, P = .004). When smell and taste parameters were included together in the regression model, both OD and GD remained significant independent predictors of dementia status based on CERAD testing (OR 3.133, P < .001, OR 1.904, P = .015).

Conclusions

OD and severe GD represent independent predictors of cognitive impairment in a nationally representative sample of older adults.