Olfactory identification is impaired in clinic-based patients with vascular dementia and senile dementia of Alzheimer type

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.

Olfactory and cognitive decrements in 1991 Gulf War veterans with gulf war illness/chronic multisymptom illness

BACKGROUND

Gulf War illness (GWI)/Chronic Multisymptom Illness (CMI) is a disorder related to military service in the 1991 Gulf War (GW). Prominent symptoms of GWI/CMI include fatigue, pain, and cognitive dysfunction. Although anosmia is not a typical GWI/CMI symptom, anecdotally some GW veterans have reported losing their sense smell shortly after the war. Because olfactory deficit is a prodromal symptom of neurodegenerative diseases like Parkinson's and Alzheimer's disease, and because we previously reported suggestive evidence that deployed GW veterans may be at increased risk for Mild Cognitive Impairment (MCI) and dementia, the current study examined the relationship between olfactory and cognitive function in deployed GW veterans.

METHODS

Eighty deployed GW veterans (mean age: 59.9  ±7.0; 4 female) were tested remotely with the University of Pennsylvania Smell Identification Test (UPSIT) and the Montreal Cognitive Assessment (MoCA). Veterans also completed self-report questionnaires about their health and deployment-related exposures and experiences. UPSIT and MoCA data from healthy control (HC) participants from the Parkinson's Progression Markers Initiative (PPMI) study were downloaded for comparison.

RESULTS

GW veterans had a mean UPSIT score of 27.8  ± 6.3 (range 9-37) and a mean MoCA score of 25.3  ± 2.8 (range 19-30). According to age- and sex-specific normative data, 31% of GW veterans (vs. 8% PPMI HCs) had UPSIT scores below the 10th percentile. Nearly half (45%) of GW veterans (vs. 8% PPMI HCs) had MoCA scores below the cut-off for identifying MCI. Among GW veterans, but not PPMI HCs, there was a positive correlation between UPSIT and MoCA scores (Spearman's ρ = 0.39, p < 0.001). There were no significant differences in UPSIT or MoCA scores between GW veterans with and without history of COVID or between those with and without Kansas GWI exclusionary conditions.

CONCLUSIONS

We found evidence of olfactory and cognitive deficits and a significant correlation between UPSIT and MoCA scores in a cohort of 80 deployed GW veterans, 99% of whom had CMI. Because impaired olfactory function has been associated with increased risk for MCI and dementia, it may be prudent to screen aging, deployed GW veterans with smell identification tests so that hypo- and anosmic veterans can be followed longitudinally and offered targeted neuroprotective therapies as they become available.

A characteristic of olfactory function in four types of dementia and non-dementia subjects using smell identification test

BACKGROUND

For those outpatients who were consulted for memory loss, the Japanese version of University of Pennsylvania Smell Identification Test (UPSIT-J) was performed to examine olfactory function. In the same way, the revised version of Hasegawa Dementia Scale, Mini Mental State Examination, Clinical Dementia Rating and brain magnetic resonance imaging were used to investigate the cognitive function. In the present study, we evaluated the olfactory function of elderly subjects, including those with dementia, by means of UPSIT-J and we examined their characteristics.

METHODS

The characteristics of dementia as Alzheimer type group (AD.G), mixed type group (MixD.G), vascular type group (VaD.G), dementia with Lewy bodies group (DLB.G) and the groups which had no dementia as low score group (LS.G), high score group (HS.G), and healthy group (H.G), were examined.

RESULTS

The numbers of olfactory discriminating scores (nODS) were significantly lower in all the dementia groups than in all the LS.G, HS.G and the H.G. No significant difference was observed in nODS between AD.G and DLB.G. The rate of nODS with less than five scores were as follows: AD.G (80.1%), MixD.G (91.5%), VaD.G (63.1%), DLB.G (89.6%), LS.G (50.8%), HS.G (18.6%), H.G (15.6%). A significant positive correlation was found between nODS and Hasegawa Dementia Scale and Mini Mental State Examination scores (r = 0.567, r = 0.532, respectively), which was significant negatively correlated for Clinical Dementia Rating (r = -0.578). A significant negative correlation was observed between nODS and Z score of voxel-based specific regional analysis for Z score of Alzheimer's disease (VSRAD) (r = 0.463).

CONCLUSION

nODS showed a significant correlation between cognitive function tests and brain atrophy level. These results indicate that UPSIT-J is considered a psycho-physiological index useful for the diagnosis and early detection of dementia.

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.

Odor Identification Across Time in Mutation Carriers and Non-Carriers in Autosomal-Dominant Alzheimer's Disease

BACKGROUND

Impaired odor identification is a characteristic of sporadic Alzheimer'sdisease(AD), but its presence in autosomal-dominantAD (adAD) remains uncertain.

OBJECTIVE

To investigate odor identification ability in mutation carriers (MC) and non-carriers (NC) of adAD in relation to years to estimated clinical onset clinical onset (YECO) of disease.

METHODS

Participants from six families with autosomal-dominant mutations (APP Swedish, APP Arctic, and PSEN1 mutations) included 20 MC and 20 NC. The groups were comparable in age, gender, education, number of APOE ɛ4 alleles, and YECO, but differed in global cognition (Mini-Mental State Examination). The MC group included individuals in asymptomatic, symptomatic cognitively unimpaired, mild cognitive impairment, and dementia stages of disease, spanning approximately 40 years of the AD continuum. All NC were asymptomatic. Olfactory function was assessed by means of free and cued identification of common odors summarized as total identification.

RESULTS

MC performed poorer than NC in free and total identification. Four MC and none of the NC were anosmic. Olfactory functions in MC and NC were significantly and inversely related to time course (YECO) for both free and total identification. The decline in free identification began approximately 10 years prior to the estimated clinical onset of AD in MC. Odor identification proficiency was associated with episodic memory and executive function in MC and NC.

CONCLUSIONS

Impaired odor identification is present well before the clinical diagnosis of AD in MC and is associated with disease progression. Odor identification ability may be a useful early biomarker for adAD.

Neuropsychological differential diagnosis of Alzheimer's disease and vascular dementia: a systematic review with meta-regressions

Introduction

Diagnostic classification systems and guidelines posit distinguishing patterns of impairment in Alzheimer's (AD) and vascular dementia (VaD). In our study, we aim to identify which diagnostic instruments distinguish them.

Methods

We searched PubMed and PsychInfo for empirical studies published until December 2020, which investigated differences in cognitive, behavioral, psychiatric, and functional measures in patients older than 64 years and reported information on VaD subtype, age, education, dementia severity, and proportion of women. We systematically reviewed these studies and conducted Bayesian hierarchical meta-regressions to quantify the evidence for differences using the Bayes factor (BF). The risk of bias was assessed using the Newcastle-Ottawa-Scale and funnel plots.

Results

We identified 122 studies with 17,850 AD and 5,247 VaD patients. Methodological limitations of the included studies are low comparability of patient groups and an untransparent patient selection process. In the digit span backward task, AD patients were nine times more probable (BF = 9.38) to outperform VaD patients (β g = 0.33, 95% ETI = 0.12, 0.52). In the phonemic fluency task, AD patients outperformed subcortical VaD (sVaD) patients (β g = 0.51, 95% ETI = 0.22, 0.77, BF = 42.36). VaD patients, in contrast, outperformed AD patients in verbal (β g = -0.61, 95% ETI = -0.97, -0.26, BF = 22.71) and visual (β g = -0.85, 95% ETI = -1.29, -0.32, BF = 13.67) delayed recall. We found the greatest difference in verbal memory, showing that sVaD patients outperform AD patients (β g = -0.64, 95% ETI = -0.88, -0.36, BF = 72.97). Finally, AD patients performed worse than sVaD patients in recognition memory tasks (β g = -0.76, 95% ETI = -1.26, -0.26, BF = 11.50).

Conclusion

Our findings show inferior performance of AD in episodic memory and superior performance in working memory. We found little support for other differences proposed by diagnostic systems and diagnostic guidelines. The utility of cognitive, behavioral, psychiatric, and functional measures in differential diagnosis is limited and should be complemented by other information. Finally, we identify research areas and avenues, which could significantly improve the diagnostic value of cognitive measures.

Sex differences in olfactory cortex neuronal loss in aging

Introduction

Aging plays a major role in neurodegenerative disorders such as Alzheimer's disease, and impacts neuronal loss. Olfactory dysfunction can be an early alteration heralding the presence of a neurodegenerative disorder in aging. Studying alterations in olfaction-related brain regions might help detection of neurodegenerative diseases at an earlier stage as well as protect individuals from any danger caused by loss of sense of smell.

Objective

To assess the effect of age and sex on olfactory cortex volume in cognitively healthy participants.

Method

Neurologically healthy participants were divided in three groups based on their age: young (20-35 years; n = 53), middle-aged (36-65 years; n = 66) and older (66-85 years; n = 95). T1-weighted MRI scans acquired at 1.5 T were processed using SPM12. Smoothed images were used to extract the volume of olfactory cortex regions.

Results

ANCOVA analyses showed significant differences in volume between age groups in the olfactory cortex (p ≤ 0.0001). In women, neuronal loss started earlier than in men (in the 4th decade of life), while in men more substantial neuronal loss in olfactory cortex regions was detected only later in life.

Conclusion

Data indicate that age-related reduction in the volume of the olfactory cortex starts earlier in women than in men. The findings suggest that volume changes in olfaction-related brain regions in the aging population deserve further attention as potential proxies of increased risk of neurodegenerative diseases.

Olfactory Dysfunction and Incidence of Motoric Cognitive Risk Syndrome: A Prospective Clinical-Pathologic Study

BACKGROUND AND OBJECTIVES

To examine associations between olfactory dysfunction, Alzheimer disease (AD) pathology, and motoric cognitive risk syndrome (MCR), a predementia syndrome characterized by cognitive complaints and slow gait that is associated with risk for AD and other dementias.

METHODS

We conducted a retrospective analysis of a prospective cohort study to examine whether baseline olfactory function was associated with the risk of incident MCR in 1,119 adults aged 60 years and older (75.1% female). The association between performance on the Brief Smell Identification Test (BSIT) and incident MCR risk was computed using Cox models and reported as the hazard ratio (HR) with 95% CIs adjusted for demographic, comorbidity, and cognitive factors. Furthermore, we assessed the relationship between postmortem AD pathology and non-AD pathology and olfactory function at the time of MCR diagnosis using linear regression models adjusted for sex, education, age at death, and time from diagnosis to death.

RESULTS

There were 544 (48.6%) incident cases of MCR over a median follow-up of 3.94 years. Lower BSIT scores (poor olfaction) at baseline were associated with an increased risk of incident MCR (HR for a 1-point increase in BSIT score 0.92; 95% CI 0.88-0.96) in fully adjusted models. Those with hyposmia (scores of ≤8 on the BSIT) at baseline (26.6%) were at an increased risk of MCR (HR 1.44; 95% CI 1.19-1.74) compared with those with normal olfactory function. Higher levels of the composite measure of global AD pathology and presence of Lewy body pathology were associated with lower BSIT scores at the time of incident MCR diagnosis (n = 118). τ tangle density, a specific component of AD pathology, was inversely associated with olfactory function, and the correlation remained after controlling for mild cognitive impairment syndrome and the presence of Lewy body pathology.

DISCUSSION

The results provide evidence that olfactory dysfunction precedes MCR incidence and is related to Alzheimer pathology, providing a clinical approach to risk stratify and subtype MCR.

International consensus statement on allergy and rhinology: Olfaction

BACKGROUND

The literature regarding clinical olfaction, olfactory loss, and olfactory dysfunction has expanded rapidly over the past two decades, with an exponential rise in the past year. There is substantial variability in the quality of this literature and a need to consolidate and critically review the evidence. It is with that aim that we have gathered experts from around the world to produce this International Consensus on Allergy and Rhinology: Olfaction (ICAR:O).

METHODS

Using previously described methodology, specific topics were developed relating to olfaction. Each topic was assigned a literature review, evidence-based review, or evidence-based review with recommendations format as dictated by available evidence and scope within the ICAR:O document. Following iterative reviews of each topic, the ICAR:O document was integrated and reviewed by all authors for final consensus.

RESULTS

The ICAR:O document reviews nearly 100 separate topics within the realm of olfaction, including diagnosis, epidemiology, disease burden, diagnosis, testing, etiology, treatment, and associated pathologies.

CONCLUSION

This critical review of the existing clinical olfaction literature provides much needed insight and clarity into the evaluation, diagnosis, and treatment of patients with olfactory dysfunction, while also clearly delineating gaps in our knowledge and evidence base that we should investigate further.

Dementia screening in rural-dwelling Chinese older adults: The utility of a smell test and the self-rated AD8

BACKGROUND

Olfactory impairment is associated with dementia in clinical settings. We examined the relationship of olfactory identification function with all-cause dementia, Alzheimer's disease (AD), and vascular dementia (VaD) and assessed the discriminative ability of the Sniffin' Sticks Identification Test (SSIT), the self-rated Ascertain Dementia 8-item Questionnaire (AD8), and their combination for dementia detection among rural-dwelling older adults in China.

METHODS

This population-based cross-sectional study included 4481 participants (age ≥ 65 years; 56.8% women; 38.1% illiteracy) living in rural communities. The 16-item SSIT was performed to assess olfactory identification function. The self-rated AD8 was administered to participants for cognitive status. We diagnosed dementia, AD, and VaD following the international criteria. Data were analyzed with logistic regression models and receiver operating characteristic curve.

RESULTS

Of the 4481 participants, dementia was diagnosed in 139 persons (3.1%), including 92 with AD and 42 with VaD. The SSIT score (range, 0-16) was associated with multiadjusted odds ratios of 0.83 (95% CI: 0.79-0.88) for dementia, 0.84 (0.79-0.90) for AD, and 0.79 (0.71-0.87) for VaD. The area under the curve for the discrimination between participants with and without dementia was 0.73 (95% CI: 0.69-0.77) for SSIT score ≤ 8 alone, 0.86 (0.82-0.89) for self-rated AD8 score ≥ 3 alone, and 0.89 (0.86-0.92) for their combination using a logistic model.

CONCLUSIONS

Olfactory impairment is a clinical marker for all-cause dementia, AD, and VaD. The smell identification test, in combination with the brief self-rated cognitive screening tool, is accurate for screening dementia among rural-dwelling Chinese older adults with no or limited education.

Objective Assessment of Hyposmia in Alzheimer's Disease From Image and Behavior by Combining Pleasant Odor With Unpleasant Odor

Background: Olfactory functional magnetic resonance imaging (fMRI) of responses to a pleasant odor (PO) (lavender) can objectively evaluate olfactory dysfunction in Alzheimer's disease (AD) patients. The brain responses to a PO and unpleasant odor (UPO) were shown to differ in normal young people. Whether AD patients with olfactory dysfunction have the same brain response is not yet known.

Objective: Our aim was to explore whether olfactory fMRI with both a PO and UPO can provide more information regarding olfactory impairment in AD than a PO alone.

Methods: Twenty-five normal controls (NC), 26 individuals with mild cognitive impairment (MCI), and 22 AD patients underwent olfactory fMRI with lavender and pyridine odorants at three concentrations (0.10, 0.33, and 1.00%) with a 3.0-T MRI scanner.

Results: There were no differences in the number of activated voxels in the primary olfactory cortex (POC) between PO and UPO conditions in the NC, MCI, and AD groups (SPM, paired t-test, uncorrected p < 0.001, extent threshold = 70). In the right inferior frontal gyrus, orbital part (F3O), the number of activated voxels was greater with the UPO than with the PO in the NC group (SPM, paired t-test, uncorrected p < 0.001, extent threshold = 70), but there were no differences in the MCI and AD groups. Regardless of PO or UPO conditions, there were significant differences in the number of activated voxels in the POC among the NC, MCI, and AD groups. With increasing odor concentration, the number of activated voxels in the POC decreased in the NC group but increased in the AD group. When 0.10% UPO was presented, the NC group (21/25) showed a lower breathing amplitude and shorter inhalation time, whereas the AD patients (0/22) did not show such changes in breathing.

Conclusions: After PO and UPO inhalation, brain activation and respiratory behavior in AD patients were significantly different than in NC patients. Therefore, olfactory fMRI using both PO and UPO stimulation, compared with PO stimulation only, can provide more objective information regarding hyposmia associated with AD based on imaging and behavior.

Olfaction as an early marker of Parkinson's disease and Alzheimer's disease

Olfactory impairment is a common and early sign of Parkinson's disease (PD) and Alzheimer's disease (AD), the two most prevalent neurodegenerative conditions in the elderly. This phenomenon corresponds to pathologic processes emerging in the olfactory system prior to the onset of typical clinical manifestations. Clinically available tests can establish hyposmia through odor identification assessment, discrimination, and odor detection threshold. There are significant efforts to develop preventative or disease-modifying therapies that slow down or halt the progression of PD and AD. Due to the convenience and low cost of its assessment, olfactory impairment could be used in these studies as a screening instrument. In the clinical setting, loss of smell may also help to differentiate PD and AD from alternative causes of Parkinsonism and cognitive impairment, respectively. Here, we discuss the pathophysiology of olfactory dysfunction in PD and AD and how it can be assessed in the clinical setting to aid in the early and differential diagnosis of these disorders.

Sleep, neuronal hyperexcitability, inflammation and neurodegeneration: Does early chronic short sleep trigger and is it the key to overcoming Alzheimer's disease?

Evidence links neuroinflammation to Alzheimer's disease (AD); however, its exact contribution to the onset and progression of the disease is poorly understood. Symptoms of AD can be seen as the tip of an iceberg, consisting of a neuropathological build-up in the brain of extracellular amyloid-β (Aβ) plaques and intraneuronal hyperphosphorylated aggregates of Tau (pTau), which are thought to stem from an imbalance between its production and clearance resulting in loss of synaptic health and dysfunctional cortical connectivity. The glymphatic drainage system, which is particularly active during sleep, plays a key role in the clearance of proteinopathies. Poor sleep can cause hyperexcitability and promote Aβ and tau pathology leading to systemic inflammation. The early neuronal hyperexcitability of γ-aminobutyric acid (GABA)-ergic inhibitory interneurons and impaired inhibitory control of cortical pyramidal neurons lie at the crossroads of excitatory/inhibitory imbalance and inflammation. We outline, with a prospective framework, a possible vicious spiral linking early chronic short sleep, neuronal hyperexcitability, inflammation and neurodegeneration. Understanding the early predictors of AD, through an integrative approach, may hold promise for reducing attrition in the late stages of neuroprotective drug development.

Olfactory Bulb Proteomics Reveals Widespread Proteostatic Disturbances in Mixed Dementia and Guides for Potential Serum Biomarkers to Discriminate Alzheimer Disease and Mixed Dementia Phenotypes

The most common form of mixed dementia (MixD) is constituted by abnormal protein deposits associated with Alzheimer's disease (AD) that coexist with vascular disease. Although olfactory dysfunction is considered a clinical sign of AD-related dementias, little is known about the impact of this sensorial impairment in MixD at the molecular level. To address this gap in knowledge, we assessed olfactory bulb (OB) proteome-wide expression in MixD subjects (n = 6) respect to neurologically intact controls (n = 7). Around 9% of the quantified proteins were differentially expressed, pinpointing aberrant proteostasis involved in synaptic transmission, nucleoside monophosphate and carbohydrate metabolism, and neuron projection regeneration. In addition, network-driven proteomics revealed a modulation in cell-survival related pathways such as ERK, AKT, and the PDK1-PKC axis. Part of the differential OB protein set was not specific of MixD, also being deregulated across different tauopathies, synucleinopathies, and tardopathies. However, the comparative functional analysis of OB proteome data between MixD and pure AD pathologies deciphered commonalities and differences between both related phenotypes. Finally, olfactory proteomics allowed to propose serum Prolow-density lipoprotein receptor-related protein 1 (LRP1) as a candidate marker to differentiate AD from MixD phenotypes.

Olfaction and Aging: A Review of the Current State of Research and Future Directions

Olfaction, the sense of smell, is characterized by a notable age-dependency such that aging individuals are more likely to have poor olfactory abilities. These impairments are considered to be mostly irreversible and as having potentially profound effects on quality of life and food behavior, as well as constituting warning signs of mortality, cognitive dysfunction, and dementia. Here, we review the current state of research on aging and olfaction, focusing on five topics which we regard to be of particular relevance for the field: nutrition and health, cognition and dementia, mortality, environment and genetics, and training-based enhancement. Under each of these headlines, we provide a state-of-the-art overview and discuss gaps in our knowledge which might be filled by further research. Understanding how olfactory abilities are diminished in aging, and how they may be alleviated or recovered, involves a set of challenging tasks for researchers in the years to come.

Measuring executive function in sheep (Ovis aries) using visual stimuli in a semi-automated operant system

BACKGROUND

Cognitive impairment is a distinguishing feature of many neurodegenerative diseases. The intra-dimensional (ID) extra-dimensional (ED) attentional set shift task is part of a clinical battery of tests used to evaluate executive function in Huntington's and Alzheimer's disease patients. The IDED task, however, has not translated well to pre-clinical rodent models of neurological disease.

NEW METHOD

The ability to perform executive tasks coupled with a long lifespan makes sheep (Ovis aries) an ideal species for modelling cognitive decline in progressive neurodegenerative conditions. We describe the methodology for testing the performance of sheep in the IDED task using a semi-automated system in which visual stimuli are presented as coloured letters on computer screens.

RESULTS

During each stage of IDED testing, all sheep (n = 12) learned successfully to discriminate between different colours and letters. Sheep were quick to learn the rules of acquisition at each stage. They required significantly more trials to reach criterion (p < 0.05) and made more errors (p < 0.05) following stimulus reversal, with the exception of the ED shift (p > 0.05).

COMPARISON WITH EXISTING METHOD(S)

Previous research shows that sheep can perform IDED set shifting in a walk-through maze using solid objects with two changeable dimensions (colour and shape) as the stimuli. Presenting the stimuli on computer screens provides better validity, greater task flexibility and higher throughput than the walk-through maze.

CONCLUSION

All sheep completed each stage of the task, with a range of abilities expected in an outbred population. The IDED task described is ideally suited as a quantifiable and clinically translatable measure of executive function in sheep.

Genomic approach to explore altered signaling networks of olfaction in response to diesel exhaust particles in mice

Airborne pollutants have detrimental effect on the human body and the environment. Diesel exhaust particles (DEPs) are known to be major component of particulate matter (PM) and cause respiratory diseases and neurotoxicity. However, the effects of air pollutants on the sensory nervous system, especially on the olfactory sense, have not been well studied. Herein, we aimed to explore DEP-induced changes in the olfactory perception process. Olfactory sensitivity test was performed after DEP inhalation in mice. Microarray was conducted to determine the differentially expressed genes, which were then utilized to build a network focused on neurotoxicity. Exposure to DEPs significantly reduced sniffing in mice, indicating a disturbance in the olfactory perception process. Through network analysis, we proposed five genes (Cfap69, Cyp26b1, Il1b, Il6, and Synpr) as biomarker candidates for DEP-mediated olfactory dysfunction. Changes in their expression might provoke malfunction of sensory transduction by inhibiting olfactory receptors, neurite outgrowth, and axonal guidance as well as lead to failure of recovery from neuroinflammatory damage through inhibition of nerve regeneration. Thus, we suggest the potential mechanism underlying DEPs-mediated olfactory disorders using genomic approach. Our study will be helpful to future researchers to assess an individual’s olfactory vulnerability following exposure to inhalational environmental hazards.

Insulin resistance is associated with impaired olfactory function in adult patients with type 1 diabetes: A cross-sectional study

AIM

To investigate whether insulin resistance is a predictor for decreased olfactory function in adult type 1 diabetes patients (T1DM).

MATERIALS AND METHODS

The following parameters were examined in the group of 113 T1DM participants: body mass index (BMI), waist-hip ratio (WHR), TG/HDL ratio, glycated hemoglobin (HbA_1c ), visceral fat (VF) in body bioimpedance, specific calculators (eGDR, VAI). Bilateral olfactory test score (BOTS) was performed using 12-odour-tests from Sniffin' Sticks. Then participants were allocated to one of two groups: normosmia (10-12 odours identified) or hyposmia/anosmia (0-9 odours). The association between BOTS and insulin resistance indicators was analyzed using: Spearman's rank correlation, multivariate linear regression analysis, and receiver operating characteristic (ROC) curve.

RESULTS

49.6% participants were diagnosed with hyposmia/anosmia, median BOTS was 10. BOTS correlated significantly with: WHR, TG, VF index, TG/HDL ratio, VAI, and eGDR. In multivariate linear regression analysis higher WHR turned out to be statistically significant independent predictor of lower BOTS (β = -0.36; P = .005) after adjustment for age, sex, TG and peripheral neuropathy (R² = 0.19; P = .0005). The ROC analysis indicated a WHR cut-off of 0.92 [area under the ROC curve (AUC): 0.737; 95% confidence interval (CI): 0.647-0.828, P < .0001] as the best among evaluated factors significantly affecting hyposmia/anosmia occurrence (sensitivity of this cut-off 0.50 and specificity 0.86).

CONCLUSIONS

We have provided evidence of an association between lowered insulin sensitivity expressed in bioelectrical impedance analysis, anthropometrical (WHR), laboratory (TG/HDL ratio) measurements, specific calculators (eGDR, VAI) and deteriorated olfactory function.

Olfactory Function Test for Early Diagnosis of Vascular Dementia

Olfactory impairment occurs in patients with Alzheimer's disease, and olfactory function tests are performed for the diagnosis of Alzheimer's disease. However, the diagnosis and patient status are not currently outlined for vascular dementia, and many physicians do not consider concurrent vascular dementia in patients complaining of olfactory dysfunction. Here, we report a case of vascular dementia with no symptoms of dementia other than olfactory dysfunction. This case suggested that the olfactory function test is helpful not only for the diagnosis of Alzheimer's disease but also for the early diagnosis of vascular dementia.

Clinical, ocular motor, and imaging profile of Niemann-Pick type C heterozygosity

Objective

To characterize subclinical abnormalities in asymptomatic heterozygote NPC1 mutation carriers as markers of neurodegeneration.

Methods

Motor function, cognition, mood, sleep, and smell function were assessed in 20 first-degree heterozygous relatives of patients with Niemann-Pick disease type C (NPC) (13 male, age 52.7 ± 9.9 years). Video-oculography and abdominal ultrasound with volumetry were performed to assess oculomotor function and size of liver and spleen. NPC biomarkers in blood were analyzed. 18F-fluorodesoxyglucose PET was performed (n = 16) to detect patterns of brain hypometabolism.

Results

NPC heterozygotes recapitulated characteristic features of symptomatic NPC disease and demonstrated the oculomotor abnormalities typical of NPC. Hepatosplenomegaly (71%) and increased cholestantriol (33%) and plasma chitotriosidase (17%) levels were present. The patients also showed signs seen in other neurodegenerative diseases, including hyposmia (20%) or pathologic screening for REM sleep behavior disorder (24%). Cognitive function was frequently impaired, especially affecting visuoconstructive function, verbal fluency, and executive function. PET imaging revealed significantly decreased glucose metabolic rates in 50% of participants, affecting cerebellar, anterior cingulate, parieto-occipital, and temporal regions, including 1 with bilateral abnormalities.

Conclusion

NPC heterozygosity, which has a carrier frequency of 1:200 in the general population, is associated with abnormal brain metabolism and functional consequences. Clinically silent heterozygous gene variations in NPC1 may be a risk factor for late-onset neurodegeneration, similar to the concept of heterozygous GBA mutations underlying Parkinson disease.

First recognized n-butanol concentration may be simple and useful index for assessing olfactory dysfunction in geriatric patients

The KVSSII is widely used to evaluate olfactory function in the Korean population. We evaluated the usefulness of the first recognized n-butanol concentration, which is obtained at the beginning part of KVSS II, in predicting olfactory dysfunction. Three hundred seventy two subjects were enrolled in our study. The results of KVSS II and the demographic characteristics were statistically analyzed. The first recognized n-butanol concentration was positively correlated with the result of KVSS II. The mean value of first recognized n-butanol concentration was 5.59 ± 1.42 in normosmia, 4.10 ± 1.40 in hyposmia, and 0.84 ± 1.68 in the anosmia group. By ROC curve, cut-off value of 2.5 showed sensitivity of 85.9% and specificity of 90.6% for anosmia, and cut-off value of 4.5 showed sensitivity of 77.6% and specificity of 69.8% for hyposmia. Consequently, we suggest that it may be useful in assessing olfactory function, in geriatric patients who are not able to tolerate conventional KVSS II.

Thymol polymeric nanoparticle synthesis and its effects on the toxicity of high glucose on OEC cells: involvement of growth factors and integrin-linked kinase

Background

Nowadays, the drug delivery system is important in the treatment of diseases.

Purpose

A polymeric nanoparticle modified by oleic acid (NPMO) as a Thymol (Thy) drug release system was synthesized from Thymbra spicata and its neurotrophic and angiogenic effects on rat’s olfactory ensheathing cells (OECs) in normal (NG) and high glucose (HG) conditions were studied.

Methods

The NPMO was characterized by using different spectroscopy methods, such as infrared, HNMR, CNMR, gel permeation chromatography, dynamic light scattering, and atomic force microscopy. Load and releasing were investigated by HPLC. The toxicity against OECs diet-induced by MTT assay. ROS and generation of nitric oxide (NO) were evaluated using dichloro-dihydro-fluorescein and Griess method, respectively. The expression of protein integrin-linked kinase (ILK), vascular endothelial growth factor (VEGF), brain-derived neurotrophic factor (BDNF), and nerve growth factor (NGF) were evaluated by Western blotting.

Results

ThyNPMO is desirable for transferring drug as a carrier. The amount of Thy and extract (E) loaded on NPMO estimated at 43±2.5% and 41±1.8%, respectively. Then, 65% and 63% of the drug load were released, respectively. Thy, ThyNPMO, E, and ENPMO prevented HG-induced OECs cell death (EC50 33±1.5, 22±0.9, 35±1.8, and 25±1.1 μM, respectively). Incubation with Thy, ThyNPMO, E ,and ENPMO at high concentrations increased cell death with LC50 105±3.5, 82±2.8, 109±4.3, and 86±3.4 μM, respectively in HG states.

Conclusion

OECs were protected by ThyNPMO and ENPMO in protective concentrations by reducing the amount of ROS and NO, maintaining ILK, reducing VEGF, and increasing BDNF and NGF. The mentioned mechanisms were totally reversed at high concentrations.

Relationships Between Lower Olfaction and Brain White Matter Lesions in Elderly Subjects with Mild Cognitive Impairment

BACKGROUND

Olfactory impairment is reported in mild cognitive impairment (MCI) and Alzheimer's disease (AD) and is associated with hippocampal atrophy. In elderly people, dementia with AD neuropathology and white matter lesions (WML) is common. In this context, olfactory impairment could also depend on the presence of WML.

OBJECTIVE

To assess the cross-sectional relationship between olfaction and WML in elderly subjects with MCI.

METHODS

Consecutive subjects, >65 years old, diagnosed as MCI after a comprehensive neuropsychological assessment in an expert memory center, with a brain MRI performed within a year and without major depressive state, were included. Olfaction was assessed by the Brief Smell Identification Test (BSIT). Two trained neuroradiologists, blind to cognitive and olfaction status, visually assessed hippocampal atrophy according to Scheltens' scale and WML according to Fazekas criteria.

RESULTS

Seventy-five MCI subjects (mean age (SD) = 77.1 (6.2) years, 74.7% of women) were included. After adjustment for age and sex, factors associated with low BSIT scores were older age (p = 0.007), lower BMI (p = 0.08), lower MMSE score (p = 0.05), lower FCRST (p = 0.008), hippocampal atrophy (p = 0.04), periventricular WML (p = 0.007), and deep WML burden (p = 0.005). In multivariate analysis, severe deep WML (OR (95% CI) = 6.29 (1.4-35.13), p = 0.02) remained associated with low BSIT score independently from hippocampal atrophy.

CONCLUSION

In elderly MCI subjects, low olfactory performances are associated with WML, whose progression may be slowed by vascular treatments. A longitudinal study to evaluate whether the progression of WML, hippocampal atrophy and low olfactory function, can predict accurately conversion from MCI to dementia is ongoing.

Chemosensory dysfunction in neurodegenerative diseases

A number of neurodegenerative diseases are accompanied by disordered smell function. The degree of dysfunction can vary among different diseases, such that olfactory testing can aid in differentiating, for example, Alzheimer's disease (AD) from major affective disorder and Parkinson's disease (PD) from progressive supranuclear palsy. Unfortunately, altered smell function often goes unrecognized by patients and physicians alike until formal testing is undertaken. Such testing uniquely probes brain regions not commonly examined in physical examinations and can identify, in some cases, patients who are already in the "preclinical" stage of disease. Awareness of this fact is one reason why the Quality Standards Committee of the American Academy of Neurology has designated smell dysfunction as one of the key diagnostic criteria for PD. The same recommendation has been made by the Movement Disorder Society for both the diagnosis of PD and identification of prodromal PD. Similar suggestions are proposed to include olfactory dysfunction as an additional research criterion for the diagnosis of AD. Although taste impairment, i.e., altered sweet, sour, bitter, salty, and umami perception, has also been demonstrated in some disorders, taste has received much less scientific attention than smell. In this review, we assess what is known about the smell and taste disorders of a wide range of neurodegenerative diseases and describe studies seeking to understand their pathologic underpinnings.

Predictors of potentially harmful behaviour by family caregivers towards patients treated for behavioural and psychological symptoms of dementia in Japan

BACKGROUND

Potentially harmful behaviour (PHB) by caregivers is detrimental to the physical and psychological well-being of care recipients. In Japan, few studies have investigated caregivers' PHB towards dementia patients. This study examined PHB in family caregivers of dementia patients with behavioural and psychological symptoms of dementia (BPSD) and identified factors related to PHB.

METHODS

Following primary consultations at an elderly psychiatric patient department, we enrolled 133 pairs of dementia patients and their family caregivers. We assessed PHB using the Japanese version of the modified Conflict Tactics Scale. We defined the presence of PHB as two or more points (PHB frequency of 'sometimes' or more) on at least one indicator of the modified Conflict Tactics Scale. We investigated the prevalence of PHB in relation to the clinical characteristics of the patients and their family caregivers. We evaluated BPSD using the Neuropsychiatric Inventory and caregiver burden using the eight-item Japanese version of the Zarit Caregiver Burden Interview.

RESULTS

Of the family caregivers, 48.9% showed PHB. Multivariate analysis identified the following association with PHB: caregiver's Zarit Caregiver Burden Interview total score (odds ratio [OR], 1.09 per unit increase; 95% confidence interval [95%CI], 1.02-1.16), and Neuropsychiatric Inventory scores for patient irritability (OR, 1.22 per unit increase; 95%CI, 1.06-1.40), appetite/eating disorders (OR, 1.41 per unit increase; 95%CI = 1.08-1.84) and daughters-in-law caregivers (OR, 0.17, 95%CI, 0.05-0.57).

CONCLUSIONS

Specific BPSD symptoms could contribute to the expression of PHB. In addition to decreasing caregiver burden, more intensive treatment and care strategies are required to manage individual symptoms.

Detectability and reproducibility of the olfactory fMRI signal under the influence of magnetic susceptibility artifacts in the primary olfactory cortex

For human olfactory functional MRI studies, the primary olfactory cortex (POC) suffers severe magnetic susceptibility artifacts, which adversely influences the detectability and reproducibility of the olfactory fMRI data and its clinical applications. The goal of this work is to assess the impacts of the image artifacts on the detectability and reproducibility of the olfactory activation in the POC. The severity of artifacts in the POC were classified into three levels using a Subjective Artifact score (SA_score). The mean temporal signal-to-noise ratio (tSNR) of the fMRI data acquired by a given MRI sequence and olfactory activation (β value) in POC were evaluated and compared to the concurrent activations in the primary visual cortex (Brodmann area 17, BA17) by an odor-visual association paradigm using ninety-nine normal human subjects. Our study revealed that the mean tSNR in POC was above the threshold for reliable detection of the functional activation signal, and, consequently, the mean olfactory activations in the POC were not significantly different from those in BA17. The reproducibility of the activation in the POC was assessed by a random half-split stimulation of a test-retest experiment. The overlap of the activation maps for all the trials (n = 1000) in the POC were not statistically different from that observed in BA17. These results show that the detectability and reproducibility of olfactory activation in the presence of susceptibility artifacts in the POC was at similar level of that in the visual cortex.

Association between diabetes mellitus and olfactory dysfunction: current perspectives and future directions

The increasing global prevalence of diabetes mellitus presents a significant challenge to healthcare systems today. Although diabetic retinopathy, nephropathy and neuropathy are well-established complications of diabetes, there is a paucity of research examining the impact of dysglycaemia on the olfactory system. Olfaction is an important sense, playing a role in the safety, nutrition and quality of life of an individual, but its importance is often overlooked when compared with the other senses. As a result, olfactory dysfunction is often underdiagnosed. The present review article aims to present and discuss the available evidence on the relationship between diabetes and olfaction. It also explores the associations between olfactory dysfunction and diabetes complications that could explain the underlying pathogenesis. Finally, it summarizes the putative pathological mechanisms underlying olfactory dysfunction in diabetes that require further investigation.

Olfactory bulb neuroproteomics reveals a chronological perturbation of survival routes and a disruption of prohibitin complex during Alzheimer's disease progression

Olfactory dysfunction is among the earliest features of Alzheimer’s disease (AD). Although neuropathological abnormalities have been detected in the olfactory bulb (OB), little is known about its dynamic biology. Here, OB- proteome analysis showed a stage-dependent synaptic proteostasis impairment during AD evolution. In addition to progressive modulation of tau and amyloid precursor protein (APP) interactomes, network-driven proteomics revealed an early disruption of upstream and downstream p38 MAPK pathway and a subsequent impairment of Phosphoinositide-dependent protein kinase 1 (PDK1)/Protein kinase C (PKC) signaling axis in the OB from AD subjects. Moreover, a mitochondrial imbalance was evidenced by a depletion of Prohibitin-2 (Phb2) levels and a specific decrease in the phosphorylated isoforms of Phb1 in intermediate and advanced AD stages. Interestingly, olfactory Phb subunits were also deregulated across different types of dementia. Phb2 showed a specific up-regulation in mixed dementia, while Phb1 isoforms were down-regulated in frontotemporal lobar degeneration (FTLD). However, no differences were observed in the olfactory expression of Phb subunits in progressive supranuclear palsy (PSP). To sum up, our data reflect, in part, the missing links in the biochemical understanding of olfactory dysfunction in AD, unveiling Phb complex as a differential driver of neurodegeneration at olfactory level.

Neuroimaging biomarkers and impaired olfaction in cognitively normal individuals

OBJECTIVE

There is a need for inexpensive noninvasive tests to identify older healthy persons at risk for Alzheimer disease (AD) for enrollment in AD prevention trials. Our objective was to examine whether abnormalities in neuroimaging measures of amyloid and neurodegeneration are correlated with odor identification (OI) in the population-based Mayo Clinic Study of Aging.

METHODS

Cognitively normal (CN) participants had olfactory function assessed using the Brief Smell Identification Test (B-SIT), underwent magnetic resonance imaging (n = 829) to assess a composite AD signature cortical thickness and hippocampal volume (HVa), and underwent ¹¹ C-Pittsburgh compound B (n = 306) and ¹⁸ fluorodeoxyglucose (n = 305) positron emission tomography scanning to assess amyloid accumulation and brain hypometabolism, respectively. The association of neuroimaging biomarkers with OI was examined using multinomial logistic regression and simple linear regression models adjusted for potential confounders.

RESULTS

Among 829 CN participants (mean age = 79.2 years; 51.5% men), 248 (29.9%) were normosmic and 78 (9.4%) had anosmia (B-SIT score < 6). Abnormal AD signature cortical thickness and reduced HVa were associated with decreased OI as a continuous measure (slope = -0.43, 95% confidence interval [CI] = -0.76 to -0.09, p = 0.01 and slope = -0.72, 95% CI = -1.15 to -0.28, p < 0.01, respectively). Reduced HVa, decreased AD signature cortical thickness, and increased amyloid accumulation were significantly associated with increased odds of anosmia.

INTERPRETATION

Our findings suggest that OI may be a noninvasive, inexpensive marker for risk stratification, for identifying participants at the preclinical stage of AD who may be at risk for cognitive impairment and eligible for inclusion in AD prevention clinical trials. These cross-sectional findings remain to be validated prospectively. Ann Neurol 2017;81:871-882.

The First Report of CADASIL in Peru: Olfactory Dysfunction on Initial Presentation

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leucoencephalopathy (CADASIL) is a rare, heritable, small vessel vascular disease caused by mutations in the Notch3 gene that is characterized by migraines, subcortical vascular events, cognitive decline, and mood disturbances. However, many CADASIL cases present with unusual symptoms such as status epilepticus, a movement disorder, or sensory dysfunction. This study describes the clinical, genetic, and radiologic characteristics of a Peruvian family with CADASIL in which multiple family members presented with severe olfactory deficits. Seven members of the family have symptoms suggestive of CADASIL, with genetic testing revealing R133C mutations in the two patients who underwent genetic testing. Cognitive testing and olfactory identification testing (Smell Identification Test) were performed in three CADASIL patients revealing total anosmia in two tested patients and severe hyposmia in the other. Olfactory dysfunction has been associated with various neurologic and psychiatric conditions though few studies have linked it with neurovascular disorders such as CADASIL. This first reported case of CADASIL in Peru emphasizes that symptomatic olfactory dysfunction may be an unusual presentation of CADASIL and that olfactory dysfunction is important to evaluate in CADASIL patients.

Progressive modulation of the human olfactory bulb transcriptome during Alzheimer´s disease evolution: novel insights into the olfactory signaling across proteinopathies

Alzheimer´s disease (AD) is characterized by progressive dementia, initially presenting olfactory dysfunction. Despite the olfactory bulb (OB) is the first central structure of the olfactory pathway, we lack a complete molecular characterization of the transcriptional events that occurs in this olfactory area during AD progression. To address this gap in knowledge, we have assessed the genome-wide expression in postmortem OBs from subjects with varying degree of AD pathology. A stage-dependent deregulation of specific pathways was observed, revealing transmembrane transport, and neuroinflammation as part of the functional modules that are disrupted across AD grading. Potential drivers of neurodegeneration predicted by network-driven transcriptomics were monitored across different types of dementia, including progressive supranuclear palsy (PSP), mixed dementia, and frontotemporal lobar degeneration (FTLD). Epidermal growth factor receptor (EGFR) expression was significantly increased in the OB of AD and mixed dementia subjects. Moreover, a significant increment in the activation of signal transducer and activator of transcription 3 (STAT3) was exclusively detected in advanced AD stages, whereas total STAT3 levels were specifically overexpressed in mixed dementia. Furthermore, transcription factors deregulated in the OB of mixed dementia subjects such as cAMP Responsive Element Binding Protein 1 (CREB1) and AP-1 Transcription Factor Subunit (c-Jun) were not differentially modulated at olfactory level across AD grading. On the other hand, olfactory expression of this signal transducer panel was unchanged in PSP and FTLD subjects. Taken together, this study unveils cross-disease similarities and differences for specific signal transducers, providing mechanistic clues to the intriguing divergence of AD pathology across proteinopathies.

Olfactory bulb proteome dynamics during the progression of sporadic Alzheimer's disease: identification of common and distinct olfactory targets across Alzheimer-related co-pathologies

Olfactory dysfunction is present in up to 90% of Alzheimer's disease (AD) patients. Although deposition of hyperphosphorylated tau and β-amyloid substrates are present in olfactory areas, the molecular mechanisms associated with decreased smell function are not completely understood. We have applied mass spectrometry-based quantitative proteomics to probe additional molecular disturbances in postmortem olfactory bulbs (OB) dissected from AD cases respect to neurologically intact controls (n=20, mean age 82.1 years). Relative proteome abundance measurements have revealed protein interaction networks progressively disturbed across AD stages suggesting an early imbalance in splicing factors, subsequent interrupted cycling of neurotransmitters, alteration in toxic and protective mechanisms of β-amyloid, and finally, a mitochondrial dysfunction together with disturbance in neuron-neuron adhesion. We also present novel molecular findings in the OB in an autopsy cohort composed by Lewy body disease (LBD), frontotemporal lobar degeneration (FTLD), mixed dementia, and progressive supranuclear palsy (PSP) cases (n = 41, mean age 79.7 years). Olfactory mediators deregulated during the progression of AD such as Visinin-like protein 1, RUFY3 protein, and Copine 6 were also differentially modulated in the OB in LBD, FTLD, and mixed dementia. Only Dipeptidyl aminopeptidase-like protein 6 showed a specific down-regulation in AD. However, no differences were observed in the olfactory expression of this protein panel in PSP subjects. This study demonstrates an olfactory progressive proteome modulation in AD, unveiling cross-disease similarities and differences especially for specific proteins involved in dendritic and axonic distributions that occur in the OB during the neurodegenerative process.

Association Between Olfactory Dysfunction and Amnestic Mild Cognitive Impairment and Alzheimer Disease Dementia

IMPORTANCE

To increase the opportunity to delay or prevent mild cognitive impairment (MCI) or Alzheimer disease (AD) dementia, markers of early detection are essential. Olfactory impairment may be an important clinical marker and predictor of these conditions and may help identify persons at increased risk.

OBJECTIVE

To examine associations of impaired olfaction with incident MCI subtypes and progression from MCI subtypes to AD dementia.

DESIGN, SETTING, AND PARTICIPANTS

Participants enrolled in the population-based, prospective Mayo Clinic Study of Aging between 2004 and 2010 were clinically evaluated at baseline and every 15 months through 2014. Participants (N = 1630) were classified as having normal cognition, MCI (amnestic MCI [aMCI] and nonamnestic MCI [naMCI]), and dementia. We administered the Brief Smell Identification Test (B-SIT) to assess olfactory function.

MAIN OUTCOMES AND MEASURES

Mild cognitive impairment, AD dementia, and longitudinal change in cognitive performance measures.

RESULTS

Of the 1630 participants who were cognitively normal at the time of the smell test, 33 died before follow-up and 167 were lost to follow-up. Among the 1430 cognitively normal participants included, the mean (SD) age was 79.5 (5.3) years, 49.4% were men, the mean duration of education was 14.3 years, and 25.4% were APOE ε4 carriers. Over a mean 3.5 years of follow-up, there were 250 incident cases of MCI among 1430 cognitively normal participants. We observed an association between decreasing olfactory identification, as measured by a decrease in the number of correct responses in B-SIT score, and an increased risk of aMCI. Compared with the upper B-SIT quartile (quartile [Q] 4, best scores), hazard ratios (HRs) (95% CI) were 1.12 (0.65-1.92) for Q3 (P = .68); 1.95 (1.25-3.03) for Q2 (P = .003); and 2.18 (1.36-3.51) for Q1 (P = .001) (worst scores; P for trend <.001) after adjustment for sex and education, with age as the time scale. There was no association with naMCI. There were 64 incident dementia cases among 221 prevalent MCI cases. The B-SIT score also predicted progression from aMCI to AD dementia, with a significant dose-response with worsening B-SIT quartiles. Compared with Q4, HR (95% CI) estimates were 3.02 (1.06-8.57) for Q3 (P = .04); 3.63 (1.19-11.10) for Q2 (P = .02); and 5.20 (1.90-14.20) for Q1 (P = .001). After adjusting for key predictors of MCI risk, B-SIT (as a continuous measure) remained a significant predictor of MCI (HR, 1.10 [95% CI, 1.04-1.16]; P < .001) and improved the model concordance.

CONCLUSIONS AND RELEVANCE

Olfactory impairment is associated with incident aMCI and progression from aMCI to AD dementia. These findings are consistent with previous studies that have reported associations of olfactory impairment with cognitive impairment in late life and suggest that olfactory tests have potential utility for screening for MCI and MCI that is likely to progress.

Olfactory dysfunction in chronic stroke patients

Background

The aim of the study was to investigate odor identification performance in patients one year after hospital admittance due to stroke. Predictors for olfactory dysfunction were investigated as well as self-reported olfactory function and pleasantness of olfactory items.

Methods

A 1-year prospective study was performed. Stroke location, classification and comorbidities were registered at hospital admission. One year after admission, olfactory function was assessed using standardized olfactory methods (screening for loss of detection sensitivity and an odor identification test). A group of matched controls was derived from a population-based study to compare odor identification performance between groups. Patients were asked for their personal judgment regarding their olfactory function and pleasantness of odorous items. In addition, global cognitive function and symptoms of depression were assessed.

Results

A total of 78 patients were enrolled (46 males, 32 females; mean age 68 years) of which 28.2 % exhibited reduced olfactory function (hyposmia) and 15.4 % exhibited loss of olfactory function (10.3 % functional anosmia, 5.1 % complete anosmia). Patients showed significantly lower olfactory performance compared to age- and sex-mated matched controls. Predictors of impaired olfactory function were age and NIHSS score. Self-reports indicated no significant differences between patients with normal olfactory function and those with reduced function. Yet, patients having an olfactory dysfunction rated odorous items as significantly less pleasant compared to patients without dysfunction.

Conclusions

Olfactory dysfunction seems to occur frequently after stoke even one year after initial admission. The deficits seem to relate to hyposmia and functional anosmia, and less to a complete loss of smell sensitivity.

A review of causal mechanisms underlying the link between age-related hearing loss and cognitive decline

Accumulating evidence points to a link between age-related hearing loss and cognitive decline, but their relationship is not clear. Does one cause the other, or does some third factor produce both? The answer has critical implications for prevention, rehabilitation, and health policy but has been difficult to establish for several reasons. First, determining a causal relationship in natural, correlational samples is problematic, and hearing and cognition are difficult to measure independently. Here, we critically review the evidence for a link between hearing loss and cognitive decline. We conclude that the evidence is convincing, but that the effects are small when hearing is measured audiometrically. We review four different directional hypotheses that have been offered as explanations for such a link, and conclude that no single hypothesis is sufficient. We introduce a framework that highlights that hearing and cognition rely on shared neurocognitive resources, and relate to each other in several different ways. We also discuss interventions for sensory and cognitive decline that may permit more causal inferences.

Smell identification function and Alzheimer's disease: a selective review

PURPOSE OF REVIEW

To provide an update of the recent studies on the olfactory function in Alzheimer's disease, with a focus on the olfactory identification function.

RECENT FINDINGS

The studies reviewed here confirm previous reports on the poor olfactory function in Alzheimer's disease compared to health normal controls and also as a marker for conversion from mild cognitive impairment to Alzheimer's disease. Olfactory identification function has been associated with severity of illness, non-cognitive neuropsychiatric symptoms, and structural and functional MRI measures. There is a possible interaction of apolipoprotein E genotype with olfactory performance in Alzheimer's disease patients and those at risk for Alzheimer's disease. Usefulness of smell identification function in differentiating Alzheimer's disease patients from other types of dementia needs to be established.

SUMMARY

The need for simple, inexpensive and non-invasive procedures for aiding in the diagnosis and understanding of Alzheimer's disease has led to theories and procedures examining the role of olfactory functions in Alzheimer's disease. Although there is increasing evidence for olfactory dysfunction in general and impaired odour identification in particular in Alzheimer's disease, additional larger and methodologically sound research is needed for testing its clinical utility in day-to-day clinical practice for early, accurate and differential diagnosis of Alzheimer's disease.

Olfactory deficits predict cognitive decline and Alzheimer dementia in an urban community

OBJECTIVE

To determine the predictive utility of baseline odor identification deficits for future cognitive decline and the diagnosis of Alzheimer disease (AD) dementia.

METHODS

In a multiethnic community cohort in North Manhattan, NY, 1,037 participants without dementia were evaluated with the 40-item University of Pennsylvania Smell Identification Test (UPSIT). In 757 participants, follow-up occurred at 2 years and 4 years.

RESULTS

In logistic regression analyses, lower baseline UPSIT scores were associated with cognitive decline (relative risk 1.067 per point interval; 95% confidence interval [CI] 1.040, 1.095; p < 0.0001), and remained significant (relative risk 1.065 per point interval; 95% CI 1.034, 1.095; p < 0.0001) after including covariates. UPSIT, but not Selective Reminding Test-total immediate recall, predicted cognitive decline in participants without baseline cognitive impairment. During follow-up, 101 participants transitioned to AD dementia. In discrete time survival analyses, lower baseline UPSIT scores were associated with transition to AD dementia (hazard ratio 1.099 per point interval; 95% CI 1.067, 1.131; p < 0.0001), and remained highly significant (hazard ratio 1.072 per point interval; 95% CI 1.036, 1.109; p < 0.0001) after including demographic, cognitive, and functional covariates.

CONCLUSIONS

Impairment in odor identification was superior to deficits in verbal episodic memory in predicting cognitive decline in cognitively intact participants. The findings support the cross-cultural use of a relatively inexpensive odor identification test as an early biomarker of cognitive decline and AD dementia. Such testing may have the potential to select/stratify patients in treatment trials of cognitively impaired patients or prevention trials in cognitively intact individuals.

The brain structural and cognitive basis of odor identification deficits in mild cognitive impairment and Alzheimer's disease

Background

The objectives of this study were to explore the relationship between olfactory impairment, cognitive measures, and brain structure volumes in healthy elderly individuals, compared to patients with amnestic mild cognitive impairment (aMCI) or early Alzheimer’s disease (AD). The primary aim was to elucidate possible differences in cognitive scores and brain structure volumes between aMCI/AD patients with relatively intact odor identification (OI) ability and those with reduced ability.

Methods

Twelve patients with aMCI, six with early AD, and 30 control subjects were included. OI abilities were assessed with the Brief Smell Identification Test (B-SIT) and Sniffin Sticks Identification Test (SSIT). Neuropsychological tests of executive functions and memory were performed. Brain structural volumes were obtained from T1 weighted 3D MRI at 3 Tesla. Statistical comparisons between the patients with aMCI and AD indicated no significant differences in performance on most tests. Since the groups were small and AD patients were in an early phase of disease, all patients were subsequently considered together as a single group for studying OI. Patients were subdivided into relatively intact (scores >50%) and reduced OI (≤ 50% score) on the olfactory tests.

Results

The aMCI/AD group with reduced OI ability, as measured by both B-SIT and SSIT, had significantly smaller hippocampal volume as compared to the patient group with OI scores > 50%. There was a significant association between OI scores and hippocampal volume in the patient (not the control) group. Similar changes with tests of executive function and memory were not found. Low OI scores on B-SIT were associated with conversion from aMCI to AD in patients. The reduced OI patient group was significantly faster on Rey complex figure copying than the fairly intact OI group.

Conclusion

The results from this pilot study suggest that the reduction in the size of hippocampus in connection with early AD is associated more with loss of OI ability rather than loss of memory, thus demonstrating that impaired OI is an early marker of medial temporal lobe degeneration.

Olfactory impairment and subjective olfactory complaints independently predict conversion to dementia: a longitudinal, population-based study

We examined whether conversion to dementia can be predicted by self-reported olfactory impairment and/or by an inability to identify odors. Common forms of dementia involve an impaired sense of smell, and poor olfactory performance predicts cognitive decline among the elderly. We followed a sample of 1529 participants, who were within a normal range of overall cognitive function at baseline, over a 10-year period during which 159 were classified as having a dementia disorder. Dementia conversion was predicted from demographic variables, Mini-Mental State Examination score, and olfactory assessments. Self-reported olfactory impairment emerged as an independent predictor of dementia. After adjusting for effects of other predictors, individuals who rated their olfactory sensitivity as "worse than normal" were more likely to convert to dementia than those who reported normal olfactory sensitivity (odds ratio [OR] = 2.17; 95% confidence interval [CI] [1.40, 3.37]). Additionally, low scores on an odor identification test also predicted conversion to dementia (OR per 1 point increase = 0.89; 95% CI [0.81, 0.98]), but these two effects were additive. We suggest that assessing subjective olfactory complaints might supplement other assessments when evaluating the risk of conversion to dementia. Future studies should investigate which combination of olfactory assessments is most useful in predicting dementia conversion.

Smell identification function as a severity and progression marker in Alzheimer's disease

BACKGROUND

Olfactory dysfunction, impaired smell identification in particular, is known as a diagnostic and a marker of conversion in Alzheimer's disease (AD). We aimed to evaluate the associations of olfactory identification impairments with cognition, illness severity, and progression in AD patients.

METHODS

Fifty-seven outpatients with late onset mild to moderate AD and 24 elderly non-demented controls (NDC) were assessed, at baseline and after three months, for Mini-Mental State Examination (MMSE), University of Pennsylvania Smell Identification Test (UPSIT), and Bristol Activities of Daily Living and Neuropsychiatry Inventory. AD participants were classified as Rapid Cognitive Decliners (RCD) defined on a priori with a loss of ≥2 points in MMSE within the previous six months.

RESULTS

AD participants had lower olfactory scores than NDC. RCD had lower olfaction scores compared with Non-Rapid Cognitive Decliners (NRCD). Although the baseline UPSIT scores were associated with baseline MMSE scores, it did not interact significantly with change in MMSE over the follow-up period. Using a median split for olfactory scores, the AD participants were classified as Rapid Olfactory Progressors (ROP) (UPSIT ≤ 15) and Slow Olfactory Progressors correlating significantly with RCD/NRCD groups. The ROP group with higher olfactory impairment indicated more symptomatic illness or severity, i.e. lower cognition, higher functional dependence, and presence of behavioral symptoms.

CONCLUSIONS

Our study supports association of smell identification function with cognition and its utility as an adjunct clinical measure to assess severity in AD. Further work, including larger longitudinal studies, is needed to explore its value in predicting AD progression.

Olfactory loss as a supporting feature in the diagnosis of Parkinson's disease: a pragmatic approach

There is ample evidence from a large number of clinical and pathological studies of an early involvement of olfactory bulbs and cortex in the Lewy body pathology in idiopathic Parkinson's disease (iPD), the olfactory system being one of the first targets of degeneration in this condition. The olfactory dysfunction may be measurably present at the time of initial presentation and progresses in a proportion of patients as the disease advances. Patients with iPD have a more severe olfactory loss as compared to multisystem atrophy whereas the syndromes of corticobasal degeneration and progressive supranuclear palsy have no olfactory loss. A proportion of drug induced parkinsonism may have olfactory loss indicative of primary pathology of dopaminergic degeneration in these patients. Unlike single photon emission tomography, formal measurement of olfaction would provide a supportive role in diagnosing or excluding iPD depending on the duration of an individual patient's parkinsonian symptoms. Whilst olfaction may be only minimally impaired in early stages and may thus not help to differentiate from other syndromes, an intact olfaction in patients with parkinsonism of few years' duration would indicate a non-iPD pathology. Olfactory measurement is easy, cheap and now easily available in a number of tests, and olfactory assessment at different stages of parkinsonism should be used as a diagnostic aid for idiopathic PD and would enhance the diagnostic accuracy of iPD when used in conjunction with the UK Parkinson's disease society Brain Bank supportive criteria for diagnosis of idiopathic Parkinson's disease.

Olfactory identification testing as a predictor of the development of Alzheimer's dementia: a systematic review

OBJECTIVES/HYPOTHESIS

To evaluate the utility of olfactory identification tests as prognostic instruments for Alzheimer's dementia (AD).

STUDY DESIGN

Systematic review.

METHODS

In accordance with PRISMA guidelines, PubMed and Ovid MEDLINE, EMBASE, ISI Web of Science, PsycINFO, the Cochrane Database of Systematic Reviews, and the Cochrane Central Register of Controlled Trials were searched to determine the quality and quantity of longitudinal and cross-sectional research on this topic.

RESULTS

Two prospective longitudinal cohort studies and 30 cross-sectional studies met inclusion criteria. The prospective longitudinal studies evaluated subjects with or without mild cognitive impairment (MCI) while also using olfactory identification testing as part of a neurocognitive evaluation. The first study reported an increased risk of later onset of AD in subjects with baseline hyposmia, whereas the second study suggested a possible relationship between decreased olfaction in participants with MCI and conversion to AD but was inconclusive due to low follow-up rates. Wide variability in the type of olfactory identification test used and the reporting of results precluded meta-analysis. The cross-sectional studies demonstrated a positive association between poorer performance on olfactory identification testing and AD.

CONCLUSIONS

Although there is evidence suggesting an association between decreased olfaction and AD, rigorously designed longitudinal cohort studies are necessary to clarify the value of olfactory identification testing in predicting the onset of AD.