Olfactory Functioning Research Articles

Olfaction and thyroid hormones in patients with subjective cognitive decline, non-amnestic and amnestic mild cognitive impairment.

Thyroid hormones may affect olfaction in different stages of cognitive impairment: subjective cognitive decline (SCD), non-amnestic (naMCI) and amnestic mild cognitive impairment (aMCI). Additionally, biometric parameters, depression, and neuropsychological performance are considered as possible influencing factors. Aretrospective single-center data analysis was conducted during the observation period 2001-2023, with n = 495 (52.3% female) SCD, naMCI and aMCI subjects, aged ≥50years, at the General Hospital of Vienna. The criterion olfactory function was objectively measured by Sniffin' Sticks© odor identification and subjectively through the Assessment of Self-Reported Olfactory Functioning test. Serum thyroid hormone levels, mainly thyroid-stimulating hormone, as well as T3, T4, fT3, and fT4, were used to assess thyroid function. Statistical analyses using IBM SPSS® 29.0.0 covered adjusted multiple linear regression models with hierarchical blocks to predict olfactory performance considering β‑weights. Of the study participants, 4.2% had hypothyroidism and 2.4% had hyperthyroidism. The majority exhibited normal thyroid function. One third (33.5%; 95% confidence interval, CI 29.4-37.0%) were hyposmic. The results indicate no substantial association between thyroid and olfactory functions. Increasing age (β = 0.20), lower performance in the Neuropsychological Test Battery Vienna (NTBV) dimensions verbal memory (β = -0.33) and attention (β = -0.12) appear to be risk factors for lower olfaction. Adiscrepancy between subjective and objective olfaction was found. Thyroid and olfactory functions had no substantial relationship. Higher fT4 correlated weakly with lower odor identification. Increasing age and decreased performance in two out of six NTBV dimensions are relevant prognostic factors for olfactory dysfunction.

Steroid responsiveness predicts olfactory function recovery in dupilumab treated CRSwNP.

There is no known predictor for olfactory function recovery with dupilumab treatment in chronic rhinosinusitis with nasal polyps (CRSwNP). This study assessed whether patient-reported recovery of olfactory function on oral corticosteroids (OCS) is a prognostic factor. Retrospective analysis of pre-biological OCS-responsiveness on olfactory functioning (OCS-responsive or OCS-unresponsive; OCS-r and OCR-u, respectively) as predictor for olfactory functioning after 6 months of dupilumab therapy for severe CRSwNP. 212 CRSwNP patients treated with dupilumab were divided between OCS-r (reported improvement of olfactory function with OCS before dupilumab treatment, n = 152), and OCS-u (OCS-unresponsive; no such improvement, n = 60). Olfactory function was tested with Sniffin's Sticks Identification Test (12 pens; SSIT-12). At baseline, both groups had a median SSIT-12 score of 3 / 12 indicating anosmia. Hyposmia and normosmia rates were also comparable (5.9% and 3.3% in OCS-r, respectively; 5.0% and 1.7% in OCS-u, respectively). After 6 months of dupilumab treatment, OCS-r showed higher olfactory scores (median SSIT-12: 8/12; 52.6% hyposmia and 17.8% normosmia) than OCS-u (median SSIT-12: 5/12; 31.7% hyposmia and 3.3% normosmia). The positive predictive value of OCS-responsiveness on scoring <7 (normosmia/hyposmia) on the SSIT-12 after 6 months of dupilumab treatment was 70.4%. Conversely, the negative predictive value of OCS-unresponsiveness on scoring <7 (anosmia) on the SSIT-12 after 6 months of dupilumab treatment was 65.0%. Patients who report olfactory function improvement on OCS have a higher chance of recovery of olfactory function during the first six months of treatment with dupilumab than patients who do not.

Differences in olfactory functioning: The role of personality and gender

AbstractThis study aimed to investigate the relationship between the gender and personality traits of individuals and their ability to detect, identify, and discriminate odors. The dataset on olfactory performance was compiled from a panel of 207 healthy human volunteers. The dataset for the odor identification test was collected using a set of 10 distinct odorants, and the odor discrimination test dataset was collected using a well‐established “Sniffin sticks” (Burghardt®, Wedel, Germany) odor discrimination test kit. To assess the Big Five personality traits of study participants, a self‐report survey questionnaire based on the International Personality Item Pool‐Neuroticism, Extraversion, and Openness (IPIP‐NEO) was used. Here, we conducted a statistical analysis to investigate the role of personality measures and gender on olfactory performance, as well as the relationship between olfactory performance and perceived odor intensity, pleasantness, and familiarity. The findings of the study suggest the existence of some relationships between gender and personality traits and odor discrimination and identification, but not odor detection. Conscientiousness and openness to experience personality traits were positively correlated with odor identification, while agreeableness and conscientiousness personality traits were positively correlated with odor discrimination. The extroversion personality scale was negatively correlated with odor discrimination. Additionally, male participants performed better than females in odor identification tasks, while females performed better in odor discrimination. The neuroticism personality domain was associated with odor identification tasks in males but not in females when analyzed separately. Correct identification of odors was also associated with their perceived familiarity.Practical ApplicationsThe results of this study may have important practical implications for a range of industries, including the fragrance and food industries. These findings may help tailor products to specific consumer preferences based on personality and gender, enhancing product appeal. Further, the fragrance and food industries can develop targeted marketing campaigns using fragrances and flavors associated with particular personality types or genders. Similarly, product testing can also be improved by representing a diverse range of personality types and genders to obtain more accurate feedback. The study insights can further guide the development of flavor and taste pairings that resonate with specific personality and gender groups. Overall, by considering olfactory differences related to personality and gender, the fragrance and food industries can segment their target markets more effectively and design products that appeal to different consumer groups.

Chronic Exposure to Environmental Pollutant Ammonia Causes Damage to the Olfactory System and Behavioral Abnormalities in Mice.

Ammonia (NH3) is a major air pollutant. However, few studies have been extended beyond the histopathological changes in the olfactory mucosa to the impact of NH3 exposure on other parts of the olfactory system and olfactory functioning. Therefore, we assessed the effects of exogenous NH3 (either 20 ppm for the low exposure group or 200 ppm for the high exposure group) on the various parts of the olfactory system by histological observation, gene expression, immunochemistry, and chemical analyses. A total of 140 Institute of Cancer Research mice (4 weeks old), 70 females and 70 males (average body weight at the start: 21.5 ± 1.9 g), were used. The exposure lasted for 4 weeks, and the mice were exposed to the NH3 for 4 h per day. Our results showed that chronic exposure to NH3 damaged the olfactory system, with consequences for changing the foraging behavior and anxiety behavior. Our results also suggest that it is plausible that NH3 recruited T cells and activated microglia cells and astrocytes, leading to inflammation in the olfactory system. Increased release of proinflammatory cytokines (TNF-α, IL-1β, IL-6, and interferon-γ) and reduced release of anti-inflammatory cytokines (IL-4 and IFN-beta) led to tissue damage and compromised the functions of the olfactory system.

A Life Without Smell: Olfactory Function in People Working in Odorless Rooms.

Odorous stimulation helps to maintain or to improve olfactory function. In contrast, odor deprivation has been suggested to facilitate olfactory impairment. The aim of this study was to investigate the effects of odor deprivation in people working in an odorless environment. Fifty people working in an odorless environment for extended periods of time and 50 people not working in such environments were recruited. The participants were examined for olfactory function (using Sniffin' Sticks), nasal airflow (using peak nasal inspiratory flowmetry), self-rated olfactory function, self-rated nasal airflow, and well-being. Correlation analyses were used to explore the associations between the duration of working in odorless environment and olfaction, nasal airflow, and well-being. The cleanroom workers exhibited slightly, but significantly reduced olfactory scores (sensitivity 7.0 ± 2.5, discrimination 11.4 ± 1.8) compared with controls (sensitivity 8.9 ± 2.5, F = 4.33, p = 0.03; discrimination 12.7 ± 1.6. F = 5.50, p = 0.001), even when controlling for age and rated nasal patency, with their self-rated olfactory function being not affected. The years of working in cleanrooms were negatively associated with olfactory function (r = 0.35, p = 0.013). No significant correlations were observed between scores of olfactory function, nasal patency, and well-being. Compared with controls cleanroom workers exhibited slightly, but significantly lower olfactory scores, nasal peak flow, and well-being. Their decreased odor sensitivity was found to be associated with the number of years they had worked in the cleanroom. Overall, these results may suggest that odorous stimulation supports olfactory functioning. 4 Laryngoscope, 134:382-387, 2024.

Global olfactory function correlates with global sexual functioning in men and women.

Olfaction is intimately involved in reproductive behaviors. However, there is limited evidence about the relationship between olfactory and sexual functioning, and whether this relationship is modulated by gender. This study aimed to investigate the correlates between olfactory and sexual functioning in a cohort of young healthy individuals; secondary outcomes were the possible correlates between disgust and perceived vulnerability to illness, with particular relation to sexual attitudes. Between January 2019 and December 2022, we enrolled 125 participants (51 males and 74 females) without known sexual disorders. The mean age was 28.47±8.6, and the mean Body Mass Index (BMI) was 23.86±3.3 without major disease or concomitant drug assumption, except for nutraceutical use. Olfactory sensitivity was tested with the Sniffin' Sticks Test (SST). Body Odor Disgust Scale (BODS) and Perceived Vulnerability to Disease (PVD) questionnaires were administered for the evaluation of perceived susceptibility to illness along with the Sexual Attitude Scale (SAS) for the evaluation of sexual attitudes. Sexual function was evaluated by the Female Sexual Function Index (FSFI) and International Index of Erectile Function (IIEF) questionnaires, respectively. Overall, a close relationship between sexual function and olfaction in both sexes (P<0.05) was found. In the male sample, better olfactive scores were positively correlated to all IIEF sub-domains but negatively with BMI and age, respectively (P<0.05). Moreover, olfaction was negatively correlated with a restrictive attitude towards sexuality (SAS) (P<0.05). The latter was also positively correlated with PVD (P<0.01). In the female sample, all FSFI subscales but sexual desire was positively correlated with olfaction (P<0.05). We herein confirm that olfactory capacities positively correlate with sexual behavior in both sexes. In males, these findings were mostly dependent upon increasing age and BMI. In females all domains of sexual function but sexual desire correlated with olfactory capacity, thus suggesting independent neural pathway activation for sexual desire. Finally, better olfactory capacities seem to determine sexual attitudes and disease avoidance behaviors irrespective of gender.

Correction to Leonhardt et al. (2019).

A sample of 124 nondemented PD patients and 154 elderly controls was assessed with the Sniffin' Sticks Odor Identification Test (OIT) and the Subjective Olfactory Capability (SOC) domain of the Assessment of Self-Reported Olfactory Functioning and Olfaction-Related Quality of Life, additional to measures of depressive symptoms, verbal memory and executive functioning. Olfactory awareness groups were formed by means of the cut-offs of the OIT and the SOC. Significant correlations between the OIT and the SOC were moderate in participants with PD and small in controls. Of all PD patients, 52% overrated their sense of smell while 27% correctly identified themselves as being hyposmic, as opposed to corresponding 6% and 1% of healthy elderly. Overrating and aware of being hyposmic participants with PD showed worse executive functions than PD patients who were objectively and subjectively normosmic. The findings imply that, although people with PD are aware of hyposmia to some extent, the majority is affected by overestimation of the ability to smell, making self-reported functioning an unreliable source of information. Moreover, reduced odor identification and impaired executive functioning might underlie the same pathological changes within the brain and could serve as a marker for cognitive impairment in PD. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Smell-related quality of life changes after total laryngectomy: a multi-centre study

PurposeA total laryngectomy creates an alternate airway for gas exchange that bypasses the upper aerodigestive tract. The subsequent reduction in nasal airflow, and therefore, reduction in deposition of particles to the olfactory neuroepithelium leads to hyposmia or anosmia. The aim of this study was to assess the quality of life impairment conferred by anosmia following laryngectomy and identify any specific patient-related risk factors that are associated with poorer outcomes.MethodsConsecutive patients with a total laryngectomy presenting for review at three tertiary head and neck services (in Australia, the United Kingdom and India) over a 12-month period were recruited. Patient demographic and clinical data were collected, and each subject completed the validated assessment of self-reported olfactory functioning and olfaction-related quality of life questionnaire (ASOF). Dichotomous comparisons were performed using the student's unpaired t-test for continuous variables (SRP), a chi-squared test for categorical variables, and a Kendall's tau-b for ordinal variables (SOC) to assess for a correlation with poorer questionnaire scores.ResultsA total of 66 laryngectomees (13.4% female; age 65.7 ± 8.6 years) were included in the study. The mean SRP score of the cohort was found to be 15.6 ± 7.4, while the mean ORQ score was noted to be 16.4 ± 8.1. No other specific risk factors associated with poorer quality of life were identified.ConclusionA significant quality of life detriment from hyposmia is conferred following laryngectomy. Further research to assess treatment options and the patient population that would best benefit from these interventions is required.

Olfactory identification, cognition, depressive symptoms, and 5-year mortality in patients with subjective cognitive decline, mild cognitive impairment, and Alzheimer's disease.

An association between odor and cognitive impairment has been shown in many studies. The objective of the present hospital-based, single-center retrospective study was to assess the impact of odor impairment on the mortality of patients with Alzheimer's disease (AD), subjective cognitive decline (SCD), and mild cognitive impairment (MCI). Odor function was measured by Sniffin Sticks (Burghart Messtechnik, Holm, Germany) and the assessment of self-reported olfactory functioning and olfaction-related quality of life (ASOF) test. Cognitive performance was assessed by an extensive neuropsychological test battery, symptoms of depression were diagnosed with the Geriatric Depressive Scale (GDS). The influence of demographic factors such as gender, age, and education were examined. Although the univariate analyses and pairwise post hoc comparison showed significant differences for some of the olfactory performance tests/subtests, the multivariate models showed no association between olfactory test performance and mortality among patients with cognitive impairment. "Attention," adomain of the Neuropsychological Test Battery Vienna (NTBV), as well as depressive symptoms, gender, and age, showed asignificant influence on the mortality of the patient group. Lower olfactory performance showed no impact on mortality. However, decreased cognitive function of "Attention" can be considered as an influential predictor for mortality.

Evaluation of COVID-19 Patients with the Assessment of Selfreported Olfactory Functioning and Olfaction-related Quality of Life Questionnaire

Evaluation of COVID-19 Patients with the Assessment of Selfreported Olfactory Functioning and Olfaction-related Quality of Life Questionnaire

Olfactory-related quality of life impacts psychological distress in people with COVID-19: The affective implications of olfactory dysfunctions

BackgroundCoronavirus disease 2019 (COVID-19) often causes chemosensory impairment, and olfactory dysfunctions may have negative consequences on psychological distress. This study aimed at assessing which dimension of perceived olfactory disfunctions (i.e., subjective olfactory capability, smell-related problems, or olfactory-related quality of life [QoL]) was most associated with psychological distress in people diagnosed with COVID-19. Methods364 participants (65 men and 299 women) diagnosed with COVID-19 on average 7 months prior to the beginning of the study were recruited between June 5 and 21, 2021, to take part in an online cross-sectional survey. Participants answered questions on demographics, clinical factors, perceived olfactory functioning, and psychological distress. Hierarchical multiple linear regression analysis was conducted, assessing the role of demographics, clinical factors, and perceived olfactory functioning dimensions on psychological distress. ResultsMore than half of the participants met the cut-off for all perceived olfactory dysfunctions scales and psychological distress. Being women, smoker, with comorbidities, and greater severity of COVID-19 symptoms were associated with higher scores on psychological distress. Among perceived olfactory functioning scales, only impairment in olfaction QoL was associated with psychological distress. LimitationsLimitations concerned the cross-sectional nature of the study and the unbalanced sample in terms of gender. ConclusionsThe study confirmed the core intertwining between mood, perceived QoL, and olfactory functioning, showing how impairments in olfactory processing are strongly correlated with psychological distress through the impact they have on the perceived QoL.

Validity and Reliability Study of the Turkish Adaptation of Taste and Smell Dysfunction Questionnaire in Hemodialysis Patients.

This study was conducted to assess the validity and reliability of the Turkish adaptation of the Taste and Smell Dysfunction Questionnaire (TSDQ) in hemodialysis patients. This study involves 125 hemodialysis patients. Research data were collected using the Descriptive Characteristics Form for Hemodialysis Patients, the TSDQ, and the Questionnaire for the Assessment of Self-Reported Olfactory Functioning and Olfaction-Related Quality of Life. In addition, the questionnaire's language and content validity, construct validity, and reliability were evaluated. With regard to content validity, a high degree of agreement was determined between expert opinions on the questionnaire items (CGI = 0.96). Exploratory factor analysis revealed that the questionnaire has a two-factor structure explaining 79.33% of the total variance. The confirmatory factor analysis demonstrated that the model is within acceptable fit index limits with factor loads between 0.692 and 0.964. The Cronbach's alpha reliability coefficients of the scale and its two sub-dimensions are 0.928, 0.968, and 0.782, respectively. The TSDQ is a valid and reliable tool for evaluating taste and smell changes in hemodialysis patients.

Odor identification testing is inferior compared to neurocognitive testing in predicting conversion to Alzheimer's Disease

IntroductionAlzheimer’s disease (AD) is a neurodegenerative disorder that affects memory, thinking, attention, and emotion or AD. Smelling problems are frequent symptoms of dementia. The aim of this study was to evaluate whether it is possible to predict if someone with anosmia or hyposmia has a higher risk of getting dementia or even AD.MethodsThis study was a retrospective longitudinal study, and the data used were part of a larger research project, the Vienna Conversion to Dementia Study. The 173 participants were divided into four groups based on cognitive features such as healthy control (HC), subjective cognitive decline (SCD), non-amnestic mild cognitive impairment (naMCI), and amnestic mild cognitive impairment (aMCI). Olfactory assessment and neurocognitive assessment were administered.ResultsWe found that 30.5% of aMCI patients converted into AD after an average of about two years. The corresponding ROC analyses for olfactory testing showed that Sniffin’ Sticks revealed significant results regarding the conversion to AD, whereas the Assessment of Self-Reported Olfactory Functioning and olfaction-related quality of life (ASOF) inventory using the Subjective Olfactory Capability (SOC) subscale, the Smell-Related Problems (SRP) subscale, and the Olfaction-Related Quality of life (ORQ) did not. A logistic regression showed that among the olfactory test procedures, only the Sniffin’ Sticks enabled a relevant prognosis. Including neurocognitive measures in the model, only VSRT and the Trail Making Test-B. The other predictors did not contribute to the prediction of conversion to AD.ConclusionUnlike self-reporting of olfactory functioning, olfactory testing using standardized tests may have potential for predicting dementia, especially AD. However, olfactory tests have lower predictive power than neurocognitive tests such as verbal memory and divided attention tests.ImplicationsDiagnostic tools for predicting dementia as accurately and early as possible are important. Olfactory assessment, compared to neurocognitive tests for verbal memory and divided attention, is inferior in predicting the prognosis of AD.

Association between environmental air pollution and olfactory functioning among Italian adolescents and young adults in Northern Italy

BACKGROUND AND AIM Olfaction is a critical physiological process with various functions in humans and olfactory impairments are associated with neurodegenerative disease and decreased quality of life. Olfactory receptors are in direct contact to ambient air, and thus, olfactory function is uniquely vulnerable to airborne pollutants. Here, we investigate associations between ambient air pollutant exposure and olfactory function in adolescents and young adults in the province of Brescia, Italy. METHODS This study included 207 subjects (52.7% female, 15-25 years) enrolled in the ongoing longitudinal Public Health Impact of Metals Exposure (PHIME) study. All participants completed a baseline (2008-2014) and follow-up (2017-2021) olfactory performance assessment using the &amp;#x22;Sniffin’ Sticks”, a psychophysical test to assess odor threshold, discrimination and identification. Spatial annual average concentrations of particulate matter (PM) PM10, PM2.5 and nitrogen dioxide (NO2) were estimated for the target area between 2016-2019 on a 4 x 4 km2 spatial resolution grid by means of the Chemical Transport Model ARIA Regional. We applied multivariable beta regression models to test for associations between each pollutant and olfactory functions. RESULTS All air pollution annual average values were below European air quality standards (mean +/- SD g/m3 PM2.5 = 18.4 +/- 5.1; PM10 = 21.0 +/- 5.3; NO2 = 32.1 +/- 9.8). We observed a significant negative association between NO2 and olfactory threshold score; a 14% decrement (approximately 2 score points) for each 10 unit increase in NO2 (p = 0.042), adjusting for age, sex, Sniffin’ identification baseline score, having a cold and/or allergic rhinitis, IQ and passive smoking exposure. CONCLUSIONS These results suggest increased NO2 exposure is associated with reduced olfactory function in these Italian adolescents and young adults. The identification of risk factors for olfactory functions can help prevent reduced quality of life and improve recovery. KEYWORDS Olfactory functions; air pollution; NO2; PM2.5; PM10

Olfactory meta-cognition in individuals with depressive and anxiety symptoms: The differential role of common and social odors

BackgroundDiminished olfactory functioning has been reported in depression, whereas evidence in anxiety disorders is still controversial. Olfactory meta-cognitive abilities (i.e., olfactory awareness, imagery and reactivity, and the importance of odors) are essential in shaping olfaction. Few studies examined these meta-cognitive abilities in relation to depressive, anxiety, and social anxiety symptoms, and none of them considered the awareness of social odors (i.e., body odors). MethodsThis pre-registered study examined the relationship between olfactory meta-cognitive abilities and symptoms of depression, general anxiety, and social anxiety in 429 individuals. Self-report measures of symptoms of depression, general anxiety, and social anxiety, along with self-report olfactory meta-cognitive scales, were collected using an online survey. ResultsLinear regression analyses revealed that olfactory awareness and importance of common odors were significantly directly predicted by symptoms of general anxiety, while affective importance to odors was negatively predicted by symptoms of depression. Regarding social odors, higher symptoms of depression and lower symptoms of social anxiety predicted increased awareness. LimitationsHigher prevalence of women and narrow age range of the participants. Depressive and anxiety symptoms were assessed only with self-report questionnaires. ConclusionsSymptoms of anxiety seem to be associated with higher levels of common odor awareness, corroborating the importance of olfactory functions in anxiety. In addition, results on social odors seem to reflect dysfunctional social behaviour that characterized symptoms of depression and social anxiety. Hence, the assessment of meta-cognitive abilities may represent a useful tool in the prevention and assessment of depressive, anxiety, and social anxiety symptoms.

Increases of Phosphorylated Tau (Ser202/Thr205) in the Olfactory Regions Are Associated with Impaired EEG and Olfactory Behavior in Traumatic Brain Injury Mice.

Traumatic brain injury (TBI) leads to long-term cognitive impairments, with an increased risk for neurodegenerative and psychiatric disorders. Among these various impairments, olfactory dysfunction is one of the most common symptoms in TBI patients. However, there are very few studies that show the association between olfactory dysfunction and repetitive TBI. To investigate the effects of repetitive TBI on olfactory functioning and the related pathological neuronal injuries in mice, we applied a weight-drop model of TBI and performed neuropathological examinations and electroencephalography (EEG) in olfactory-bulb-associated areas. Through neuropathological examinations, we found significant increases of amyloid precursor protein (APP) and phosphorylated Tau (p-Tau) (S202/T205) in olfactory-bulb-associated areas. Neuronal atrophy in the lateral anterior olfactory nucleus (AOL), granule layer olfactory bulb (GrO), and dorsal tenia tecta (DTT) was also found to be correlated with p-Tau levels. However, there was no difference in the total Tau levels in the olfactory-bulb-associated areas of TBI mice. Electroencephalography (EEG) of repetitive TBI mouse models showed impaired spontaneous delta oscillation, as well as altered cross-frequency coupling between delta phase and amplitudes of the fast oscillations in the resting-state olfactory bulb. Furthermore, abnormal alterations in EEG band powers were observed during the olfactory oddball paradigm test. TBI also led to impairments of the olfactory-function-associated behaviors. This study provides evidence of behavioral, neuropathological, and physiological alterations in the mouse olfactory system caused by repetitive TBI. Together, p-Tau alterations and EEG impairments may serve as important biomarkers of olfactory-track-associated dysfunctions in repetitive TBI.

Olfactory Function and Depression: A Meta-Analysis.

We investigated the relationship between olfactory function and depression and suggested future research in this area from rhinology. We independently searched 5 databases (PubMed, SCOPUS, Embase, the Web of Science, and the Cochrane database) for recent studies published from December 2019 to the present. From the obtained studies, we reviewed the findings on olfactory function and depression using a questionnaire to measure depression and olfactory tests. The olfactory function test score based on the UPSIT-40 (standardized mean difference = -.37 [-.66; -.08], P = .0123) was significantly lower in the depression group than in the control group. The olfactory function score based on the Sniffin' sticks test for identification, discrimination, and threshold was lower in the depression group than in the control. A meta-analysis of the studies showed that depressed patients showed lower olfactory function than the control group. The findings revealed that an understanding of the relationship between olfaction and depression can be determined using an analysis methodology and a standardized olfactory test. Olfactory functioning and processing are highly integrated with emotion and memory through projections from the olfactory bulb to the central areas.

Neuroimmunoendocrine Link Between Chronic Kidney Disease and Olfactory Deficits.

Chronic kidney disease (CKD) is a multifactorial pathology that progressively leads to the deterioration of metabolic functions and results from deficient glomerular filtration and electrolyte imbalance. Its economic impact on public health is challenging. Mexico has a high prevalence of CKD that is strongly associated with some of the most common metabolic disorders like diabetes and hypertension. The gradual loss of kidney functions provokes an inflammatory state and endocrine alterations affecting several systems. High serum levels of prolactin have been associated with CKD progression, inflammation, and olfactory function. Also, the nutritional status is altered due to impaired renal function. The decrease in calorie and protein intake is often accompanied by malnutrition, which can be severe at advanced stages of the disease. Nutrition and olfactory functioning are closely interconnected, and CKD patients often complain of olfactory deficits, which ultimately can lead to deficient food intake. CKD patients present a wide range of deficits in olfaction like odor discrimination, identification, and detection threshold. The chronic inflammatory status in CKD damages the olfactory epithelium leading to deficiencies in the chemical detection of odor molecules. Additionally, the decline in cognitive functioning impairs the capacity of odor differentiation. It is not clear whether peritoneal dialysis and hemodialysis improve the olfactory deficits, but renal transplants have a strong positive effect. In the present review, we discuss whether the olfactory deficiencies caused by CKD are the result of the induced inflammatory state, the hyperprolactinemia, or a combination of both.

Olfactory Function and Diffusion Tensor Imaging as Markers of Mild Cognitive Impairment in Early Stages of Parkinson's Disease.

Parkinson's disease (PD) is a neurodegenerative disorder that is typified by motor signs and symptoms but can also lead to significant cognitive impairment and dementia Parkinson's Disease Dementia (PDD). While dementia is considered a nonmotor feature of PD that typically occurs later, individuals with PD may experience mild cognitive impairment (PD-MCI) earlier in the disease course. Olfactory deficit (OD) is considered another nonmotor symptom of PD and often presents even before the motor signs and diagnosis of PD. We examined potential links among cognitive impairment, olfactory functioning, and white matter integrity of olfactory brain regions in persons with early-stage PD. Cognitive tests were used to establish groups with PD-MCI and with normal cognition (PD-NC). Olfactory functioning was examined using the University of Pennsylvania Smell Identification Test (UPSIT) while the white matter integrity of the anterior olfactory structures (AOS) was examined using magnetic resonance imaging (MRI) diffusion tensor imaging (DTI) analysis. Those with PD-MCI demonstrated poorer olfactory functioning and abnormalities based on all DTI parameters in the AOS, relative to PD-NC individuals. OD and microstructural changes in the AOS of individuals with PD may serve as additional biological markers of PD-MCI.

Olfactory Decline in Older Adults with Mild Cognitive Impairment with and without Comorbidities.

Over the past two decades, several studies have measured olfactory performance in Mild Cognitive Impairment (MCI). Deficits are observed in multiple olfactory domains, including odour detection threshold, identification, discrimination, and memory. In this study, the psychophysiological Sniffin’ Sticks smell screening test was administered to examine olfactory functioning in 145 older adults with MCI, a group with MCI and chronic comorbid conditions, and a healthy age-matched comparison group. We hypothesised that olfactory performance will deteriorate in the two MCI groups compared to the control group, even after assessing the known contributions of age and gender. The higher olfactory deterioration in the group with the MCI and the comorbidities in the first year disappeared in the second. This could mean that early consideration of the potential effect of other comorbidities that might affect olfaction should be taken and addressed, as they could easily mask the effect of cognitive decline and/or contribute to it. This study also found higher deterioration in smell identification in participants with MCI, as has been found repeatedly in similar research. Olfactory identification seems to be a more robust marker for discriminating people with MCI and without, and even discriminating between those with MCI and having other health problems.