Anosmia in dementia is associated with Lewy bodies rather than Alzheimer's pathology

A pathophysiological biomarker combination separates Lewy body from non-Lewy body neurogenic orthostatic hypotension ​

PURPOSE

Neurogenic orthostatic hypotension (nOH) results from deficient reflexive delivery of norepinephrine to cardiovascular receptors in response to decreased cardiac venous return. Lewy body (LB) forms of nOH are characterized by low 18F-dopamine-derived radioactivity (a measure of cardiac noradrenergic deficiency), olfactory dysfunction by the University of Pennsylvania Smell Identification Test (UPSIT), and increased deposition of alpha-synuclein (α-syn) in dermal sympathetic noradrenergic nerves by the α-syn-tyrosine hydroxylase (TH) colocalization index. This observational, cross-sectional study explored whether combinations of these biomarkers specifically identify LB forms of nOH.

METHODS

Clinical laboratory data were reviewed from patients referred for evaluation at the National Institutes of Health for chronic autonomic failure between 2011 and 2023. The cutoff value for low myocardial 18F-dopamine-derived radioactivity was 6000 nCi-kg/cc-mCi, for olfactory dysfunction an UPSIT score ≤ 28, and for an increased α-syn-TH colocalization index ≥ 1.57.

RESULTS

A total of 44 patients (31 LB, 13 non-LB nOH) had data for all three biomarkers. Compared to the non-LB group, the LB nOH group had low myocardial 18F-dopamine-derived radioactivity, low UPSIT scores, and high α-syn-TH colocalization indexes (p < 0.0001 each). Combining the three biomarkers completely separated the groups. Cluster analysis identified two distinct groups (p < 0.0001) independently of the clinical diagnosis, with one cluster corresponding exactly to LB nOH.

CONCLUSION

LB forms of nOH feature cardiac noradrenergic deficiency, olfactory dysfunction, and increased α-syn-TH colocalization in skin biopsies. Combining the data for these variables efficiently separates LB from non-LB nOH. Independently of the clinical diagnosis, this biomarker triad identifies a pathophysiologically distinct cluster of nOH patients.

Intra-neuronal alpha-synuclein deposition is related to cardiac noradrenergic deficiency and olfactory dysfunction in neurogenic orthostatic hypotension

Purpose

Neurogenic orthostatic hypotension (nOH) results from deficient reflexive delivery of norepinephrine to cardiovascular receptors in response to decreased cardiac venous return. Lewy body (LB) forms of nOH entail low 18F-dopamine-derived radioactivity (a measure of cardiac noradrenergic deficiency), olfactory dysfunction by the University of Pennsylvania Smell Identification Test (UPSIT), and increased deposition of alpha-synuclein (ɑ-syn) in dermal sympathetic noradrenergic nerves by the ɑ-syn-tyrosine hydroxylase (TH) colocalization index. This observational, cross-sectional study explored whether combinations of these biomarkers specifically identify LB forms of nOH.

Methods

Clinical laboratory data were reviewed from patients referred for evaluation at the National Institutes of Health for chronic autonomic failure between 2011 and 2023. The cutoff value for low myocardial 18F-dopamine-derived radioactivity was 6,000 nCi-kg/cc-mCi, for olfactory dysfunction an UPSIT score ≤ 28, and for an increased ɑ-syn-TH colocalization index ≥ 1.57.

Results

A total of 44 patients (31 LB, 13 non-LB nOH) had data for all 3 biomarkers. Compared to the non-LB group, the LB nOH group had low myocardial 18F-dopamine-derived radioactivity, low UPSIT scores, and high ɑ-syn-TH colocalization indexes (p<0.0001 each). Combining the 3 biomarkers completely separated the groups. Cluster analysis identified 2 distinct groups (p<0.0001) independently of the clinical diagnosis, 1 cluster corresponding exactly to LB nOH.

Conclusion

LB forms of nOH feature cardiac noradrenergic deficiency, olfactory dysfunction, and increased ɑ-syn-TH colocalization in skin biopsies. Combining the data for these variables efficiently separates LB from non-LB nOH. Independently of the clinical diagnosis, this biomarker triad identifies a pathophysiologically distinct cluster of nOH patients.

Eating problems in people with dementia with Lewy bodies: Associations with various symptoms and the physician's understanding

OBJECTIVES

Eating problems frequently occur in people with dementia with Lewy bodies (DLB), but few studies have investigated the clinical background of this phenomenon. This study examined the relationship between eating problems and various symptoms of DLB and the relation between the treatment needs for DLB people with eating problems and the understanding of their eating problems by caregivers and physicians.

DESIGN, MEASUREMENTS, AND PARTICIPANTS

This was a subanalysis of a cross-sectional, questionnaire-based survey study. Two hundred sixty-one subjects with DLB were divided into subjects with or without eating problems. Logistic or linear regression analysis was used to investigate the factors influencing eating problems. The treatment needs of DLB people for their eating problems and the understanding of these needs by caregivers and physicians were calculated as participant-caregiver and participant-physician kappa coefficient.

RESULTS

Of the 261 participants, 27% suffered from eating problems. The presence of eating problems in participants with DLB was related to depression (p = 0.01, OR : 2.19, 95% CI: 1.23-3.91) and apathy (p = 0.01, OR 2.15, 95% CI: 1.20-3.87), while the worsening of eating problems was related to dysphagia (β = 0.24, p = 0.03), apathy (β = 0.23, p = 0.05), and nighttime behavior (β = 0.24, p = 0.04). The participant-physician kappa coefficient for physician understanding of constipation, weight loss, dysphagia, weight gain, and increase in appetite was significantly lower than the corresponding participant-caregiver kappa coefficient (p-value of five symptoms < 0.01).

CONCLUSIONS

Physicians need to pay more attention to eating problems and their neuropsychiatric background in the long-term support and management of DLB subjects.

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.

Investigating the potential effects of α-synuclein aggregation on susceptibility to chronic stress in a mouse Parkinson's disease model

BACKGROUND

Parkinson's disease (PD) is a motor disorder characterized by the degeneration of dopaminergic neurons, putatively due to the accumulation of α-synuclein (α-syn) in Lewy bodies (LBs) in Substantia Nigra. PD is also associated with the formation of LBs in brain areas responsible for emotional and cognitive regulation such as the amygdala and prefrontal cortex, and concurrent depression prevalence in PD patients. The exact link between dopaminergic cell loss, α-syn aggregation, depression, and stress, a major depression risk factor, is unclear. Therefore, we aimed to explore the interplay between sensitivity to chronic stress and α-syn aggregation.

METHODS

Bilateral injections of α-syn preformed fibrils (PFFs) into the striatum of C57Bl/6 J mice were used to induce α-syn aggregation. Three months after injections, animals were exposed to chronic social defeat stress.

RESULTS

α-syn aggregation did not affect stress susceptibility but independently caused increased locomotor activity in the open field test, reduced anxiety in the light-dark box test, and increased active time in the tail suspension test. Ex vivo analysis revealed modest dopaminergic neuron loss in the substantia nigra and reduced dopaminergic innervation in the dorsal striatum in PFFs injected groups. α-Syn aggregates were prominent in the amygdala, prefrontal cortex, and substantia nigra, with minimal α-syn aggregation in the raphe nuclei and locus coeruleus.

CONCLUSIONS

Progressive bilateral α-syn aggregation might lead to compensatory activity increase and alterations in emotionally regulated behavior, without affecting stress susceptibility. Understanding how α-syn aggregation and degeneration in specific brain structures contribute to depression and anxiety in PD patients requires further investigation.

Brain olfactory-related atrophy in isolated rapid eye movement sleep behavior disorder

OBJECTIVE

To investigate structural and functional connectivity changes in brain olfactory-related structures in a longitudinal prospective cohort of isolated REM sleep behavior disorder (iRBD) and their clinical correlations, longitudinal evolution, and predictive values for phenoconversion to overt synucleinopathies, especially Lewy body diseases.

METHODS

The cohort included polysomnography-confirmed iRBD patients and controls. Participants underwent baseline assessments including olfactory tests, neuropsychological evaluations, the Movement Disorders Society-Unified Parkinson's Disease Rating Scale, 3T brain MRI, and 18 F-FP-CIT PET scans. Voxel-based morphometry (VBM) was performed to identify regions of atrophy in iRBD, and volumes of relevant olfactory-related regions of interest (ROI) were estimated. Subgroups of patients underwent repeated volumetric MRI and resting-state functional MRI (fMRI) scans after four years.

RESULTS

A total of 51 iRBD patients were included, with 20 of them converting to synucleinopathy (mean time to conversion 3.08 years). Baseline VBM analysis revealed atrophy in the right olfactory cortex and gyrus rectus in iRBD. Subsequent ROI comparisons with controls showed atrophy in the amygdala. These olfactory-related atrophies tended to be associated with worse depression, anxiety, and urinary problems in iRBD. Amygdala 18 F-FP-CIT uptake tended to be reduced in iRBD patients with hyposmia (nonsignificant after multiple comparison correction) and correlated with urinary problems. Resting-state fMRI of 23 patients and 32 controls revealed multiple clusters with aberrant olfactory-related functional connectivity. Hypoconnectivity between the putamen and olfactory cortex was associated with mild parkinsonian signs in iRBD. Longitudinal analysis of volumetric volumetric MRI in 22 iRBD patients demonstrated four-year progression of olfactory-related atrophy. Cox regression analysis revealed that this atrophy significantly predicted phenoconversion.

INTERPRETATION

Progressive atrophy of central olfactory structures may be a potential indicator of Lewy body disease progression in iRBD.

Aberrant corticospinal tract characteristics in prodromal PD: A diffusion tensor imaging study

Introduction

Parkinson's disease (PD) is typically diagnosed when motor symptoms first occur. However, PD-related non-motor symptoms may appear several years before diagnosis. REM sleep behaviour disorder (RBD) and olfactory deficits (hyposmia) are risk factors, but they are not specific for predicting progression towards PD. Other PD-related markers, for example brain imaging markers, may help to identify preclinical PD in hyposmic RBD patients. Studies have reported abnormal structural characteristics in the corticospinal tract (CST) of PD patients, but it is unclear whether hyposmic RBD patients have similar abnormalities that may help to predict PD in these individuals. This study examined whether CST abnormalities may be a potential marker of PD risk by using diffusion tensor imaging (DTI) measures.

Methods

Twenty hyposmic RBD patients, 31 PD patients, and 29 healthy controls (HCs) were studied. DTI data were collected on a 1.5 T MRI scanner and CST characteristics (FA, MD, AD, and RD) were evaluated using probabilistic tractography (with seed regions in the bilateral primary motor cortex and mediolateral cerebral peduncles). Olfactory function was assessed with the University of Pennsylvania Smell Identification Test (UPSIT).

Results

Hyposmic RBD patients showed significantly higher mean diffusivity (MD) values of the right CST compared to HCs but did not differ from PD patients. PD patients showed a trend of higher MD values compared to HCs.

Conclusions

Altered diffusivity in the CST seems to be associated with RBD. The combination of RBD, hyposmia, and CST alterations may be related to later development of PD with comorbid RBD.

Olfactory impairment in mild cognitive impairment with Lewy bodies and Alzheimer's disease

OBJECTIVES

Impaired olfaction may be a biomarker for early Lewy body disease, but its value in mild cognitive impairment with Lewy bodies (MCI-LB) is unknown. We compared olfaction in MCI-LB with MCI due to Alzheimer's disease (MCI-AD) and healthy older adults. We hypothesized that olfactory function would be worse in probable MCI-LB than in both MCI-AD and healthy comparison subjects (HC).

DESIGN

Cross-sectional study assessing olfaction using Sniffin' Sticks 16 (SS-16) in MCI-LB, MCI-AD, and HC with longitudinal follow-up. Differences were adjusted for age, and receiver operating characteristic (ROC) curves were used for discriminating MCI-LB from MCI-AD and HC.

SETTING

Participants were recruited from Memory Services in the North East of England.

PARTICIPANTS

Thirty-eight probable MCI-LB, 33 MCI-AD, 19 possible MCI-LB, and 32HC.

MEASUREMENTS

Olfaction was assessed using SS-16 and a questionnaire.

RESULTS

Participants with probable MCI-LB had worse olfaction than both MCI-AD (age-adjusted mean difference (B) = 2.05, 95% CI: 0.62-3.49, p = 0.005) and HC (B = 3.96, 95% CI: 2.51-5.40, p < 0.001). The previously identified cutoff score for the SS-16 of ≤ 10 had 84% sensitivity for probable MCI-LB (95% CI: 69-94%), but 30% specificity versus MCI-AD. ROC analysis found a lower cutoff of ≤ 7 was better (63% sensitivity for MCI-LB, with 73% specificity vs MCI-AD and 97% vs HC). Asking about olfactory impairments was not useful in identifying them.

CONCLUSIONS

MCI-LB had worse olfaction than MCI-AD and normal aging. A lower cutoff score of ≤ 7 is required when using SS-16 in such patients. Olfactory testing may have value in identifying early LB disease in memory services.

ER Stress in COVID-19 and Parkinson’s Disease: In Vitro and In Silico Evidences

The outbreak of COVID-19 caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) signifies a serious worldwide concern to public health. Both transcriptome and proteome of SARS-CoV-2-infected cells synergize the progression of infection in host, which may exacerbate symptoms and/or progression of other chronic diseases such as Parkinson’s disease (PD). Oxidative stress is a well-known cause of endoplasmic reticulum (ER) stress observed in both SARS-CoV-2 and PD. In the current study, we aimed to explore the influence of PKR-like ER kinase (PERK) stress pathway under SARS-CoV-2-mediated infection and in human cell model of PD. Furthermore, we investigated whether they are interconnected and if the ER stress inhibitors could inhibit cell death and provide cellular protection. To achieve this aim, we have incorporated in silico analysis obtained from gene set enrichment analysis (GSEA), a literature review and laboratory data. The neurotoxin, 6-hydroxy dopamine (6OHDA), was used to mimic the biochemical and neuropathological characteristics of PD by inducing oxidative stress in dopamine-containing neurons differentiated from ReNVM cell line (dDCNs). Furthermore, we explored if ER stress influences activation of caspases-2, -4 and -8 in SARS-CoV-2 and in stressed dDCNs. Our laboratory data using Western blot, immunocytochemistry and 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide (MTT) analyses indicated that 6OHDA-induced toxicity triggered activation of caspases-2, -4 and -8 in dDCNs. Under SARS-CoV-2 infection of different cell types, GSEA revealed cell-specific sensitivities to oxidative and ER stresses. Cardiomyocytes and type II alveolar epithelial-like cells were more vulnerable to oxidative stress than neural cells. On the other side, only cardiomyocytes activated the unfolded protein response, however, the PERK pathway was operative in both cardiomyocytes and neural cells. In addition, caspase-4 activation by a SARS-CoV-2 was observed via in silico analyses. These results demonstrate that the ER stress pathway under oxidative stress in SARS-CoV-2 and PD are interconnected using diverse pathways. Furthermore, our results using the ER stress inhibitor and caspase specific inhibitors provided cellular protection suggesting that the use of specific inhibitors can provide effective therapeutic approaches for the treatment of COVID-19 and PD.

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

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

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.

Could COVID-19 anosmia and olfactory dysfunction trigger an increased risk of future dementia in patients with ApoE4?

The association of the coronavirus disease 2019 (COVID-19) with significant neurological and neuropsychiatric complications has been increasingly reported, both during the acute illness and in its aftermath. However, due to the short duration of patient follow up until now, it is not clear whether this infection will be associated with longer-term neurological and/or neuropsychiatric sequelae. In particular, the question of whether COVID-19 will be associated with an increased risk and rate of future dementia remains open and subject to speculation. During the course of the COVID-19 pandemic, an increasing number of patients have reported sudden anosmia or other olfactory dysfunction as concurrent symptoms. The possibility that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) may reach the brain via the olfactory nerve or an upper nasal trancribrial route is an interesting working hypothesis. Among the identified genetic risk factors for Late-onset Alzheimer’s disease (LOAD), Apo E4 is one of the strongest and most frequent. People carrying one or two copies of the e4 allele of Apo E4 have significant odor recognition deficits in comparison to those not carrying this haplotype.

The hypothesis invoked in this paper is that anosmia/olfactory dysfunctions induced by SARS-CoV-2 may cause an increased a risk of future neurodegenerative dementia in ApoE4 carriers, and that this risk would be higher than in Apo E4 carriers affected by anosmia not induced by SARS-CoV-2. This would be associated with virus-induced chronic modifications in the central nervous system. It is proposed that COVID-19 patients with anosmia and no other serious symptoms should be followed up as part of specifically designed and approved studies in order to identify the early stages of dementia (especially LOAD and Dementia with Lewy Bodies), thereby improving our knowledge of the mechanisms involved in pre-cognitive stages of neurodegenerative dementia and making best use of any available therapies. This latter opportunity is unique and should not be lost.

Could Early Identification of Changes in Olfactory Function Be an Indicator of Preclinical Neurodegenerative Disease? A Systematic Review

INTRODUCTION

Alzheimer's disease (AD) is a debilitating neurodegenerative disease that currently affects 850,000 individuals in the UK with estimates continuing to rise. Diagnosis is only available in the presence of significant neuronal pathology and apparent cognitive decline, meaning that treatment avenues are often limited and carry little to no effect on prognosis. Olfactory function has been shown to have a direct correlation with cognitive function and therefore may serve as a potential diagnostic tool for the detection of preclinical disease. The objective was to examine the current literature to establish the accuracy of olfactory function testing in determining current and future cognitive function.

METHODS

A systematic review was performed via Medline on 17 October 2019 using the search terms and Boolean operators 'Dementia OR Alzheimer's AND olfaction AND cognitive impairment' yielding 111 results. These were then screened using inclusion/exclusion criteria alongside a PICO strategy. After titles, abstracts and full text were screened, nine articles were included in the review and critically appraised using the AXIS and CASP tools.

RESULTS

Significant correlations are demonstrated between olfactory impairment (OI) and cognitive decline. However, there were limitations of many of the studies in that confounders such as head trauma, upper respiratory infection (URTI) and smoking history were not considered. The majority of the studies also used an olfactory screening tool that was not designed for the population being examined.

CONCLUSION

Despite improvements in olfactory testing needing to be implemented, OI is clearly impaired in neurodegenerative disease across a multitude of ages and cultures, offering an early marker of future cognitive decline. As a result of the heterogenous nature of the included studies, there is a further need for future research to ensure the sensitivity, validity and reliability of implementing olfactory testing as an early marker of future cognitive decline.

Proteomic Characterization of the Olfactory Molecular Imbalance in Dementia with Lewy Bodies

Olfactory dysfunction is one of the prodromal symptoms in dementia with Lewy bodies (DLB). However, the molecular pathogenesis associated with decreased smell function remains largely undeciphered. We generated quantitative proteome maps to detect molecular alterations in olfactory bulbs (OB) derived from DLB subjects compared to neurologically intact controls. A total of 3214 olfactory proteins were quantified, and 99 proteins showed significant alterations in DLB cases. Protein interaction networks disrupted in DLB indicated an imbalance in translation and the synaptic vesicle cycle. These alterations were accompanied by alterations in AKT/MAPK/SEK1/p38 MAPK signaling pathways that showed a distinct expression profile across the OB–olfactory tract (OT) axis. Taken together, our data partially reflect the missing links in the biochemical understanding of olfactory dysfunction in DLB.

Thyroid Hormone and Neural Stem Cells: Repair Potential Following Brain and Spinal Cord Injury

Neurodegenerative diseases are characterized by chronic neuronal and/or glial cell loss, while traumatic injury is often accompanied by the acute loss of both. Multipotent neural stem cells (NSCs) in the adult mammalian brain spontaneously proliferate, forming neuronal and glial progenitors that migrate toward lesion sites upon injury. However, they fail to replace neurons and glial cells due to molecular inhibition and the lack of pro-regenerative cues. A major challenge in regenerative biology therefore is to unveil signaling pathways that could override molecular brakes and boost endogenous repair. In physiological conditions, thyroid hormone (TH) acts on NSC commitment in the subventricular zone, and the subgranular zone, the two largest NSC niches in mammals, including humans. Here, we discuss whether TH could have beneficial actions in various pathological contexts too, by evaluating recent data obtained in mammalian models of multiple sclerosis (MS; loss of oligodendroglial cells), Alzheimer’s disease (loss of neuronal cells), stroke and spinal cord injury (neuroglial cell loss). So far, TH has shown promising effects as a stimulator of remyelination in MS models, while its role in NSC-mediated repair in other diseases remains elusive. Disentangling the spatiotemporal aspects of the injury-driven repair response as well as the molecular and cellular mechanisms by which TH acts, could unveil new ways to further exploit its pro-regenerative potential, while TH (ant)agonists with cell type-specific action could provide safer and more target-directed approaches that translate easier to clinical settings.

Effect of A/T/N imaging biomarkers on impaired odor identification in Alzheimer's disease

Odor identification ability may serve as an important diagnostic biomarker in Alzheimer’s disease (AD). The aim of the study is to investigate the contribution of A/T/N neuroimaging biomarkers to impaired odor identification ability in the Alzheimer’s disease spectrum. In 127 participants, we compared A/T/N neuroimaging biomarkers between normosmia and hyposmia groups, and performed correlation analysis between the biomarkers and Cross-Cultural Smell Identification Test (CCSIT) scores. Additionally, path analysis for odor identification ability was performed using cognitive function as a mediator. In between-group comparison, individuals with hyposmia showed higher frequency of amyloid-β (Aβ) positivity, and lower neuropsychological test performance than those with normosmia. After correction for covariates including total cognition scores, there was no difference in the Aβ or tau burden between the normosmia and hyposmia groups, and no correlation between CCSIT scores and Aβ or tau burden. Meanwhile, cortical volumes in the lateral and medial temporal cortices were smaller in the hyposmia group and decreased with the worsening of CCSIT scores. Path analysis showed that only neurodegeneration had a direct effect on odor identification, while Aβ and tau burden contributed to odor identification with the mediation of cognition. In the Alzheimer’s disease spectrum, impaired odor identification ability may be attributable to neurodegeneration rather than the direct effect of Aβ or tau burden.

The insula, a grey matter of tastes: a volumetric MRI study in dementia with Lewy bodies

Background

Despite the growing number of discoveries during the past decades about its functions, the insula remains a mysterious ‘island’. In addition to its involvement in basic functions such as gustation and interoception, the insular cortex is now considered a key region for integrated functions such as emotion/motivation processing, decision-making and self-consciousness. We hypothesized that this structure, standing at the crossroads of such functions, could ground personal tastes in general, beyond food preferences and aesthetic judgements. Given that dementia with Lewy bodies is characterized by a focal atrophy within the insular cortex from the early stages, this condition provides an opportunity to test such a hypothesis.

Methods

We developed a questionnaire to assess potential changes in personal tastes, submitted it to a cohort of 23 patients with early-stage dementia with Lewy bodies and compared their questionnaire results to those of 20 age-matched healthy controls. Furthermore, we performed a global and regional neuroimaging study to test for a potential correlation between the patients’ scores for changes in personal tastes and their insular cortex volumes.

Results

Our results indicate that the patients presented significant changes in personal tastes compared to the controls, in both food and non-food domains. Moreover, imaging analyses confirmed the involvement of the insular cortex atrophy in the changes in personal tastes using global analysis, and in both food and non-food domains using regional analysis.

Conclusions

These results bring new insights into the role of the insula as a ‘grey matter of tastes’, this structure supporting personal preferences in general, beyond the food domain. The insular cortex could be involved through its role in motivational processes by the representation of subjective awareness of bodily states during the phenomenological experience of stimulus appraisal. However, we also argue that it could support the abstract representations of personal tastes as self-concepts, acutely exemplifying embodied cognition. Finally, the questionnaire on changes in tastes could constitute an interesting tool to help early diagnosis of dementia with Lewy bodies and to assess insular dysfunction more generally.

Severe hyposmia distinguishes neuropathologically confirmed dementia with Lewy bodies from Alzheimer's disease dementia

Many subjects with neuropathologically-confirmed dementia with Lewy bodies (DLB) are never diagnosed during life, instead being categorized as Alzheimer's disease dementia (ADD) or unspecified dementia. Unrecognized DLB therefore is a critical impediment to clinical studies and treatment trials of both ADD and DLB. There are studies that suggest that olfactory function tests may be able to distinguish DLB from ADD, but few of these had neuropathological confirmation of diagnosis. We compared University of Pennsylvania Smell Identification Test (UPSIT) results in 257 subjects that went on to autopsy and neuropathological examination. Consensus clinicopathological diagnostic criteria were used to define ADD and DLB, as well as Parkinson's disease with dementia (PDD), with (PDD+AD) or without (PDD-AD) concurrent AD; a group with ADD and Lewy body disease (LBD) not meeting criteria for DLB (ADLB) and a clinically normal control group were also included. The subjects with DLB, PDD+AD and PDD-AD all had lower (one-way ANOVA p < 0.0001, pairwise Bonferroni p < 0.05) first and mean UPSIT scores than the ADD, ADLB or control groups. For DLB subjects with first and mean UPSIT scores less than 20 and 17, respectively, Firth logistic regression analysis, adjusted for age, gender and mean MMSE score, conferred statistically significant odds ratios of 17.5 and 18.0 for the diagnosis, vs ADD. For other group comparisons (PDD+AD and PDD-AD vs ADD) and UPSIT cutoffs of 17, the same analyses resulted in odds ratios ranging from 16.3 to 31.6 (p < 0.0001). To our knowledge, this is the largest study to date comparing olfactory function in subjects with neuropathologically-confirmed LBD and ADD. Olfactory function testing may be a convenient and inexpensive strategy for enriching dementia studies or clinical trials with DLB subjects, or conversely, reducing the inclusion of DLB subjects in ADD studies or trials.

Association of innervation-adjusted alpha-synuclein in arrector pili muscles with cardiac noradrenergic deficiency in autonomic synucleinopathies

BACKGROUND

Autonomic synucleinopathies feature deposition of the protein alpha-synuclein (AS) in neurons [e.g., Lewy body neurogenic orthostatic hypotension (nOH)] or glial cells (multiple system atrophy, MSA). AS in skin biopsies might provide biomarkers of these diseases; however, this approach would be complicated or invalidated if there were substantial loss of AS-containing nerves. We report AS content in arrector pili muscles in skin biopsies after adjustment for local innervation in patients with Lewy body nOH or MSA. Cardiac sympathetic neuroimaging by myocardial ¹⁸F-dopamine positron emission tomography (PET) was done to examine pathophysiological correlates of innervation-adjusted AS.

METHODS

Thirty-one patients (19 Lewy body nOH, 12 MSA) underwent thoracic ¹⁸F-dopamine PET and skin biopsies. AS signal intensity analyzed by immunofluorescence microscopy was adjusted for innervation by the ratio of AS to protein gene product (PGP) 9.5, a pan-axonal marker (Harvard lab site), or the ratio of AS to tyrosine hydroxylase (TH), an indicator of catecholaminergic neurons (NIH lab site).

RESULTS

The Lewy body nOH group had higher ratios of AS/PGP 9.5 or log AS/TH than did the MSA group (0.89 ± 0.05 vs. 0.66 ± 0.04, -0.13 ± 0.05 vs. -1.60 ± 0.33; p < 0.00001 each). All 19 Lewy body patients had AS/PGP 9.5 > 0.8 or log AS/TH > 1.2 and had myocardial ¹⁸F-dopamine-derived radioactivity < 6000 nCi-kg/cc-mCi, the lower limit of normal. Two MSA patients (17%) had increased AS/PGP or log AS/TH, and two (17%) had low ¹⁸F-dopamine-derived radioactivity.

CONCLUSIONS

Lewy body forms of nOH are associated with increased innervation-adjusted AS in arrector pili muscles and neuroimaging evidence of myocardial noradrenergic deficiency.

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.

Advances in markers of prodromal Parkinson disease

Efforts to develop neuroprotective therapy for Parkinson disease (PD) are focusing on the early stages of disease, which offer the best opportunity to intervene. Early PD can be divided into preclinical, prodromal and clinical stages; in this Review, we focus on the prodromal stage and markers that can be used to identify prodromal PD. We consider the necessary properties of a marker, before providing an overview of the proven and potential markers of prodromal PD, including clinical nonmotor markers, clinical motor markers, neuroimaging markers and tissue biomarkers. Markers for which the ability to predict conversion to PD is supported by the strongest evidence include olfactory loss, REM sleep behaviour disorder and constipation. Markers with the highest diagnostic strength include REM sleep behaviour disorder, dopaminergic imaging and subtle motor parkinsonism. The lead time - the period between the appearance of a marker and conversion to PD - is highly variable between markers, ranging from 5 years for impaired motor performance to >20 years for autonomic symptoms. The cost of screening for these markers also varies dramatically: some require just questionnaires, whereas others require sophisticated scanning techniques. Finally, we summarize how prodromal and risk markers can be combined to estimate the probability that an individual has prodromal PD, with a focus on the International Parkinson Disease and Movement Disorders Society (MDS) Prodromal Parkinson Criteria.

Ablation of tau causes an olfactory deficit in a murine model of Parkinson's disease

Parkinson's disease is diagnosed upon the presentation of motor symptoms, resulting from substantial degeneration of dopaminergic neurons in the midbrain. Prior to diagnosis, there is a lengthy prodromal stage in which non-motor symptoms, including olfactory deficits (hyposmia), develop. There is limited information about non-motor impairments and there is a need for directed research into these early pathogenic cellular pathways that precede extensive dopaminergic death in the midbrain. The protein tau has been identified as a genetic risk factor in the development of sporadic PD. Tau knockout mice have been reported as an age-dependent model of PD, and this study has demonstrated that they develop motor deficits at 15-months-old. We have shown that at 7-month-old tau knockout mice present with an overt hyposmic phenotype. This olfactory deficit correlates with an accumulation of α-synuclein, as well as autophagic impairment, in the olfactory bulb. This pathological feature becomes apparent in the striatum and substantia nigra of 15-month-old tau knockout mice, suggesting the potential for a spread of disease. Initial primary cell culture experiments have demonstrated that ablation of tau results in the release of α-synuclein enriched exosomes, providing a potential mechanism for disease spread. These alterations in α-synuclein level as well as a marked autophagy impairment in the tau knockout primary cells recapitulate results seen in the animal model. These data implicate a pathological role for tau in early Parkinson's disease.

Olfactory dysfunction in Alzheimer's disease- and Lewy body-related cognitive impairment

INTRODUCTION

Olfactory dysfunction is common in Alzheimer's disease- and Lewy body-related disorders, but its neural correlates have not been clearly elucidated.

METHODS

We retrospectively recruited 237 patients with Alzheimer's disease-related cognitive impairment (ADCI) and 217 with Lewy body-related cognitive impairment (LBCI). They were identically evaluated using the Cross-Cultural Smell Identification Test, neuropsychological tests, and brain magnetic resonance imaging.

RESULTS

LBCI had more severe olfactory dysfunction than ADCI. Patients with more severe cognitive dysfunction had worse olfactory function in both groups. In ADCI, lower Cross-Cultural Smell Identification Test scores correlated with a lower cortical thickness in brain regions typically affected in Alzheimer's disease, most prominently in the right parahippocampal cortex, whereas in LBCI, the scores correlated with white matter abnormalities in regions vulnerable to Lewy body, including subcortical regions of the orbitofrontal and frontoparietal cortices.

DISCUSSION

Our results suggest that cortical atrophy in ADCI and white matter abnormalities in LBCI play important roles in olfactory dysfunction.

Olfactory Dysfunction in Neurodegenerative Diseases

PURPOSE OF REVIEW

The sense of smell is today one of the focuses of interest in aging and neurodegenerative disease research. In several neurodegenerative diseases, such as Parkinson's disease and Alzheimer's disease, the olfactory dysfunction is one of the initial symptoms appearing years before motor symptoms and cognitive decline, being considered a clinical marker of these diseases' early stages and a marker of disease progression and cognitive decline. Overall and under the umbrella of precision medicine, attention to olfactory function may help to improve chances of success for neuroprotective and disease-modifying therapeutic strategies.

RECENT FINDINGS

The use of olfaction, as clinical marker for neurodegenerative diseases is helpful in the characterization of prodromal stages of these diseases, early diagnostic strategies, differential diagnosis, and potentially prediction of treatment success. Understanding the mechanisms underlying olfactory dysfunction is central to determine its association with neurodegenerative disorders. Several anatomical systems and environmental factors may underlie or contribute to olfactory loss associated with neurological diseases, although the direct biological link to each disorder remains unclear and, thus, requires further investigation. In this review, we describe the neurobiology of olfaction, and the most common olfactory function measurements in neurodegenerative diseases. We also highlight the evidence for the presence of olfactory dysfunction in several neurodegenerative diseases, its value as a clinical marker for early stages of the diseases when combined with other clinical, biological, and neuroimage markers, and its role as a useful symptom for the differential diagnosis and follow-up of disease. The neuropathological correlations and the changes in neurotransmitter systems related with olfactory dysfunction in the neurodegenerative diseases are also described.

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.

The olfactory bulb as the entry site for prion-like propagation in neurodegenerative diseases

Olfactory deficits are present in numerous neurodegenerative disorders and are accompanied by pathology in related brain regions. In several of these disorders, olfactory disturbances appear early and are considered as prodromal symptoms of the disease. In addition, pathological protein aggregates affect olfactory regions prior to other regions, suggesting that the olfactory system might be particularly vulnerable to neurodegenerative diseases. Exposed to the external environment, the olfactory epithelium and olfactory bulb allow pathogen and toxin penetration into the brain, a process that has been proposed to play a role in neurodegenerative diseases. Determining whether the olfactory bulb could be a starting point of pathology and of pathology spread is crucial to understanding how neurodegenerative diseases evolve. We argue that pathological changes following environmental insults contribute to the initiation of protein aggregation in the olfactory bulb, which then triggers the spread of the pathology within the brain by a templating mechanism in a prion-like manner. We review the evidence for the early involvement of olfactory structures in neurodegenerative diseases and the relationship between neuropathology and olfactory function. We discuss the vulnerability and putative underlying mechanisms by which pathology could be initiated in the olfactory bulb, from the entry of pathogens (promoted by increased permeability of the olfactory epithelium with aging or inflammation) to the sensitivity of the olfactory system to oxidative stress and inflammation. Finally, we review changes in protein expression and neural excitability triggered by pathogenic proteins that can promote pathogenesis in the olfactory bulb and beyond.

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.

Sensorineural Organs Dysfunction and Cognitive Decline: A Review Article

Vision, hearing, olfaction, and cognitive function are essential components of healthy and successful aging. Multiple studies demonstrate relationship between these conditions with cognitive function. The present article focuses on hearing loss, visual impairment, olfactory loss, and dual sensory impairments in relation to cognitive declination and neurodegenerative disorders. Sensorineural organ impairment is a predictive factor for mild cognitive impairment and neurodegenerative disorders in the elderly. We recommend early detection of sensorineural dysfunction by history, physical examination, and screening tests. Assisted device and early cognitive rehabilitation may be beneficial. Future research is warranted in order to explore advanced treatment options and method to slow progression for cognitive declination and sensorineural organ impairment.

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.

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.

Olfactory function and neuropsychological profile to differentiate dementia with Lewy bodies from Alzheimer's disease in patients with mild cognitive impairment: A 5-year follow-up study

BACKGROUND

Mild cognitive impairment (MCI) is a well-known precursor of Alzheimer's disease (AD) but often also precedes dementia with Lewy bodies (DLB). The early differentiation of DLB from AD is important to delay disease progression. Olfactory dysfunction is a well-known early sign of both AD and Lewy body disorders, including Parkinson's disease (PD) and DLB. Thus, the aim of the present study was to determine whether olfactory and neuropsychological tests can aid in the differentiation of DLB from AD at the MCI stage.

METHODS

The present study included 122 MCI patients who were monitored until they developed dementia or until their condition stabilized; the follow-up period averaged 4.9 years (range: 3.9-6.2 years). Baseline olfactory function as measured with the Cross-Cultural Smell Identification (CCSI) test and neuropsychological data were compared.

RESULTS

During the follow-up period, 32 subjects developed probable AD (MCI-AD), 18 had probable DLB (MCI-DLB), 45 did not convert to dementia (MCI-stable), and eight developed a non-AD/DLB dementia. The mean CCSI score (95% confidence interval [CI]) in patients with MCI-DLB (4.6; 95% CI: 4.0-5.3) was significantly lower than that of MCI-AD patients (6.4; 95% CI: 6.0-6.7, p<0.001) and MCI-stable patients (7.3; 95% CI: 6.9-7.8, p<0.001). The area under the curve of the receiver operating characteristic to discriminate MCI-DLB from MCI-AD using CCSI scores was (0.84; 95% CI: 0.72-0.97). Frontal-executive function and visuospatial ability was worse in patients with MCI-DLB, while verbal recognition memory impairment was greater in those with MCI-AD.

CONCLUSION

Olfactory and neuropsychological tests can help predict conversion to DLB or AD in patients with MCI.

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.

Aromatherapy for dementia

BACKGROUND

Complementary therapy has received great interest within the field of dementia treatment and the use of aromatherapy and essential oils is increasing. In a growing population where the majority of patients are treated by US Food and Drug Administration (FDA)-approved drugs, the efficacy of treatment is short term and accompanied by negative side effects. Utilisation of complimentary therapies in dementia care settings presents as one of few options that are attractive to practitioners and families as patients often have reduced insight and ability to verbally communicate adverse reactions. Amongst the most distressing features of dementia are the behavioural and psychological symptoms. Addressing this facet has received particular interest in aromatherapy trials, with a shift in focus from reducing cognitive dysfunction to the reduction of behavioural and psychological symptoms in dementia.

OBJECTIVES

To assess the efficacy of aromatherapy as an intervention for people with dementia.

SEARCH METHODS

ALOIS, the Cochrane Dementia and Cognitive Improvement Group Specialized Register, was searched on 26 November 2012 and 20 January 2013 using the terms: aromatherapy, lemon, lavender, rose, aroma, alternative therapies, complementary therapies, essential oils.

SELECTION CRITERIA

All relevant randomised controlled trials were considered. A minimum length of a trial and requirements for follow-up were not included, and participants in included studies had a diagnosis of dementia of any type and severity. The review considered all trials using fragrance from plants defined as aromatherapy as an intervention with people with dementia and all relevant outcomes were considered.

DATA COLLECTION AND ANALYSIS

Titles and abstracts extracted by the searches were screened for their eligibility for potential inclusion in the review. For Burns 2011, continuous outcomes were estimated as the mean difference between groups and its 95% confidence interval using a fixed-effect model. For Ballard 2002, analysis of co-variance was used for all outcomes, with the nursing home being treated as a random effect.

MAIN RESULTS

Seven studies with 428 participants were included in this review; only two of these had published usable results. Individual patient data were obtained from one trial (Ballard 2002) and additional analyses performed. The additional analyses conducted using individual patient data from Ballard 2002 revealed a statistically significant treatment effect in favour of the aromatherapy intervention on measures of agitation (n = 71, MD -11.1, 95% CI -19.9 to -2.2) and behavioural symptoms (n = 71, MD -15.8, 95% CI -24.4 to -7.2). Burns 2011, however, found no difference in agitation (n = 63, MD 0.00, 95% CI -1.36 to 1.36), behavioural symptoms (n = 63, MD 2.80, 95% CI -5.84 to 11.44), activities of daily living (n = 63, MD -0.50, 95% CI -1.79 to 0.79) and quality of life (n = 63, MD 19.00, 95% CI -23.12 to 61.12). Burns 2011 and Fu 2013 found no difference in adverse effects (n = 124, RR 0.97, 95% CI 0.15 to 6.46) when aromatherapy was compared to placebo.

AUTHORS' CONCLUSIONS

The benefits of aromatherapy for people with dementia are equivocal from the seven trials included in this review. It is important to note there were several methodological difficulties with the included studies. More well-designed, large-scale randomised controlled trials are needed before clear conclusions can be drawn regarding the effectiveness of aromatherapy for dementia. Additionally, several issues need to be addressed, such as whether different aromatherapy interventions are comparable and the possibility that outcomes may vary for different types of dementia.

Considering the senses in the diagnosis and management of dementia

Associations between dementia and impairments in hearing, vision, olfaction and (to a lesser degree) taste have been identified. Hearing impairment has been shown to precede cognitive decline, but it is not clear if the hearing loss is an early marker of dementia or a modifiable risk factor. Olfactory impairment is seen in many neurodegenerative conditions, but it has been shown that those with dementia have particular difficulties with the recognition and identification of odours rather than the detection, suggesting a link to impairment of higher cognitive function. Olfactory impairment has been shown to be predictive of conversion from mild cognitive impairment to Alzheimer's disease with 85.2% sensitivity. As cognitive function deteriorates, the world is experienced at a sensory level, with reduced ability to integrate the sensory experiences to understand the context. Thus, people with dementia are very sensitive to sensory experiences and their environment needs to be managed carefully to make it understandable, comfortable, and (if possible) therapeutic. Light can be used to stabilise the circadian rhythm, which may be disturbed in dementia. Music therapy, aromatherapy, massage and multisensory stimulation are recommended by NICE for the management of behavioural and psychological symptoms of dementia (BPSD), although the mechanisms behind such interventions are poorly understood and evidence is limited. Sensory considerations are likely to play a greater role in dementia care in the future, with the development of purpose-built dementia care facilities and the focus on non-pharmacological management strategies for BPSD.

Olfactory identification and cognitive performance in community-dwelling older adults with mild cognitive impairment

Olfactory impairment constitutes one of the earliest signs of Alzheimer's disease in older adults with mild cognitive impairment. We investigated which aspects of neuropsychological measures are correlated with olfactory identification performance among older adults with mild cognitive impairment. Total of 220 participants with mild cognitive impairment (mean age 71.7 years) were examined. Odor identification was assessed using the Open Essence test. Participants underwent comprehensive neurocognitive evaluation, including measures of verbal memory, visual memory, working memory, attention/executive function, and processing speed. We examined associations between olfactory function and cognitive performance scores. Participants with severe hyposmia exhibited significantly poor verbal and visual memory performance, attention/executive function, and slower processing speed scores compared with those without severe hyposmia. In multivariable logistic regression models, better performance scores on verbal and visual memory were significantly associated with decreased likelihood of severe hyposmia after adjusting for age, sex, education, and other cognitive performance scores. These findings suggest that olfactory impairment might be more closely associated with memory loss compared with other aspects of cognitive functioning in mild cognitive impairment subjects.

Reduced cholinergic olfactory centrifugal inputs in patients with neurodegenerative disorders and MPTP-treated monkeys

Olfactory impairment is a common feature of neurodegenerative diseases such as Parkinson's disease (PD), Alzheimer's disease (AD) and dementia with Lewy bodies (DLB). Olfactory bulb (OB) pathology in these diseases shows an increased number of olfactory dopaminergic cells, protein aggregates and dysfunction of neurotransmitter systems. Since cholinergic denervation might be a common underlying pathophysiological feature, the objective of this study was to determine cholinergic innervation of the OB in 27 patients with histological diagnosis of PD (n = 5), AD (n = 14), DLB (n = 8) and 8 healthy control subjects. Cholinergic centrifugal inputs to the OB were clearly reduced in all patients, the most significant decrease being in the DLB group. We also studied cholinergic innervation of the OB in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated monkeys (n = 7) and 7 intact animals. In MPTP-monkeys, we found that cholinergic innervation of the OB was reduced compared to control animals (n = 7). Interestingly, in MPTP-monkeys, we also detected a loss of cholinergic neurons and decreased dopaminergic innervation in the horizontal limb of the diagonal band, which is the origin of the centrifugal cholinergic input to the OB. All these data suggest that cholinergic damage in the OB might contribute, at least in part, to the olfactory dysfunction usually exhibited by these patients. Moreover, decreased cholinergic input to the OB found in MPTP-monkeys suggests that dopamine depletion in itself might reduce the cholinergic tone of basal forebrain cholinergic neurons.

The olfactory system in Alzheimer’s disease: Pathology, pathophysiology and pathway for therapy

Olfaction is frequently mentioned as a “neglected sense”, although the olfactory system has several interesting and unique anatomical and physiological features. Olfactory involvement is present in several degenerative disorders, especially in Alzheimer’s disease (AD). The peripheral and central parts of the olfactory system are damaged even in the early stages of AD, manifesting in profound olfactory deficits. Besides the early pathology, the olfactory system may be involved in the pathogenesis of AD by providing a route of entry for pathological agents still unknown. In contrast to this olfactory vector hypothesis, the olfactory system can be used to deliver therapeutic agents in AD, such as nerve growth factor and insulin, by decreasing the side-effects of the therapy or providing a non-invasive method of delivery.

Premotor symptoms and early diagnosis of Parkinson's disease

Parkinson's disease is a disorder characterized by the motor findings of bradykinesia, rest tremor, cogwheel rigidity, and postural instability. As the disease progresses, most patients develop numerous nonmotor signs and symptoms, many of which play a major role in reducing quality of life. What is becoming increasingly clear is that nonmotor findings, including hyposmia, sleep disorders, autonomic abnormalities, cognitive changes, and neurobehavioral changes, often precede the motor findings.

Olfaction in Parkinson's disease and related disorders

Olfactory dysfunction is an early 'pre-clinical' sign of Parkinson's disease (PD). The present review is a comprehensive and up-to-date assessment of such dysfunction in PD and related disorders. The olfactory bulb is implicated in the dysfunction, since only those syndromes with olfactory bulb pathology exhibit significant smell loss. The role of dopamine in the production of olfactory system pathology is enigmatic, as overexpression of dopaminergic cells within the bulb's glomerular layer is a common feature of PD and most animal models of PD. Damage to cholinergic, serotonergic, and noradrenergic systems is likely involved, since such damage is most marked in those diseases with the most smell loss. When compromised, these systems, which regulate microglial activity, can influence the induction of localized brain inflammation, oxidative damage, and cytosolic disruption of cellular processes. In monogenetic forms of PD, olfactory dysfunction is rarely observed in asymptomatic gene carriers, but is present in many of those that exhibit the motor phenotype. This suggests that such gene-related influences on olfaction, when present, take time to develop and depend upon additional factors, such as those from aging, other genes, formation of α-synuclein- and tau-related pathology, or lowered thresholds to oxidative stress from toxic insults. The limited data available suggest that the physiological determinants of the early changes in PD-related olfactory function are likely multifactorial and may include the same determinants as those responsible for a number of other non-motor symptoms of PD, such as dysautonomia and sleep disturbances.

Proteomic atlas of the human olfactory bulb

The olfactory bulb (OB) is the first site for the processing of olfactory information in the brain and its deregulation is associated with neurodegenerative disorders. Although different efforts have been made to characterize the human brain proteome in depth, the protein composition of the human OB remains largely unexplored. We have performed a comprehensive analysis of the human OB proteome employing protein and peptide fractionation methods followed by LC-MS/MS, identifying 1529 protein species, corresponding to 1466 unique proteins, which represents a 7-fold increase in proteome coverage with respect to previous OB proteome descriptions from translational models. Bioinformatic analyses revealed that protein components of the OB participated in a plethora of biological process highlighting hydrolase and phosphatase activities and nucleotide and RNA binding activities. Interestingly, 631 OB proteins identified were not previously described in protein datasets derived from large-scale Human Brain Proteome Project (HBPP) studies. In particular, a subset of these differential proteins was mainly involved in axon guidance, opioid signaling, neurotransmitter receptor binding, and synaptic plasticity. Taken together, these results increase our knowledge about the molecular composition of the human OB and may be useful to understand the molecular basis of the olfactory system and the etiology of its disorders.

Lewy bodies and olfactory dysfunction in old age

As part of a clinical-pathologic project, older people completed a standard odor identification test at study entry. During a mean of 3.5 years of observation, 201 people died and underwent brain autopsy and neuropathologic examination (6 with a history of Parkinson's disease were excluded). Lewy bodies were identified with antibodies to alpha-synuclein and classified as nigral, limbic, or neocortical based on their distribution in 6 brain regions. Plaques and tangles in 5 regions were summarized with a previously established composite measure, and neuron loss in the substantia nigra was rated on 6-point scale. Odor identification scores ranged from 0 to 12 correct (mean = 8.0, standard deviation = 2.6). On neuropathologic examination, 26 persons had Lewy bodies (13 neocortical, 9 limbic, and 4 nigral). In an analysis adjusted for age, sex, education, and time from olfactory testing to death, limbic (estimate = -2.47, standard error [SE] = 0.73, P < 0.001) and neocortical (estimate = -4.36, SE = 0.63, P < 0.001) Lewy body subgroups were associated with impaired olfaction. Results were comparable in analyses that controlled for dementia or parkinsonism during the study or postmortem measures of plaques and tangles or nigral cell loss. A final set of analyses suggested that impaired olfactory performance may aid detection of underlying Lewy body disease. The findings indicate that Lewy body disease impairs late life olfactory function even in otherwise asymptomatic individuals.

Idiopathic REM Sleep Behavior Disorder: Implications for the Pathogenesis of Lewy Body Diseases

Objectives. Both results of the odor identification and cardiac (123)I-metaiodobenzylguanidine accumulation have been investigated for their potential to enhance the detection of pathogenesis resembling that of Lewy body-related α-synucleinopathies in patients clinically diagnosed as having idiopathic REM sleep behavior disorder. Methods. We performed both the Odor Stick Identification Test for Japanese and (123)I-metaiodobenzylguanidine scintigraphy in 30 patients with idiopathic REM sleep behavior disorder, 38 patients with Parkinson's disease, and 20 control subjects. Results. In idiopathic REM sleep behavior disorder, reduced odor identification score and an early or delayed heart to mediastinum ratio on (123)I-metaiodobenzylguanidine were almost as severe as in Parkinson's disease patients. Delayed cardiac (123)I-metaiodobenzylguanidine uptake was even more severe in the idiopathic REM sleep behavior disorder group than in the Parkinson's disease group. Conclusions. Reduced cardiac (123)I-metaiodobenzylguanidine uptake, which is independent of parkinsonism, may be more closely associated with idiopathic REM sleep behavior disorder than olfactory impairment.

Odor identification deficits are associated with increased risk of neuropsychiatric complications in patients with Parkinson's disease

Olfactory deficits appear early in the course of Parkinson's disease (PD) but their prognostic significance is not known. The goal of this study was to determine whether the severity of olfactory impairment is associated with subsequent risk of developing complications of PD. One hundred patients with PD self-administered the University of Pennsylvania Smell Identification Test (UPSIT). Testing was done, on average, 3.6 years from the time of initial diagnosis. The incidence of neuropsychiatric features of PD, including cognitive decline and visual hallucinations, was ascertained through chart review after an average of 6.8 years of follow-up. Incidence of motor outcomes including falls and dyskinesias was also obtained. There was a significant trend for increased risk of neuropsychiatric complications across declining quartiles of olfactory test scores. In addition, subjects in the lowest quartile of olfactory performance had a significantly higher adjusted risk of hallucinations (HR = 4.70, 95% CI 1.64, 13.42) and cognitive decline (HR = 3.10, 95% CI 1.05, 9.21) than those in the reference quartile. There was no association between olfactory dysfunction and dyskinesias, and a very modest association with risk of falls. These findings suggest that severity of olfactory impairment early in the disease course may be a useful marker for the risk of neuropsychiatric complications of PD.

123I-MIBG cardiac uptake and smell identification in parkinsonian patients with LRRK2 mutations

Reduced uptake of (123)I- metaiodobenzylguanidine (MIBG) on cardiac gammagraphy and impaired odor identification are markers of neurodegenerative diseases with Lewy bodies (LB) as a pathological hallmark, such as idiopathic Parkinson's disease (IPD). LRRK2 patients present with a clinical syndrome indistinguishable from IPD, but LB have not been found in some cases. Patients with such mutations could behave differently than patients with IPD with respect to MIBG cardiac uptake and olfaction. We studied 14 LRRK2 patients, 14 IPD patients matched by age, gender, disease duration and severity, and 13 age and gender matched control subjects. Olfaction was analyzed through the University of Pennsylvania Smell Identification Test (UPSIT). MIBG cardiac uptake was evaluated through the H/M ratio. The late H/M was 1.44 ± 0.31 for LRRK2 patients, 1.19 ± 0.15 for PD patients, and 1.67 ± 0.16 for control subjects. LRRK2 patients presented lower but not statistically significant MIBG cardiac uptake than controls (p = 0.08) and significant higher uptake than PD patients (p = 0.04). UPSIT mean scores were 21.5 ± 7.3 for LRRK2 patients, 18.7 ± 6.2 for IPD patients and 29.7 ± 5.7 for control subjects. UPSIT score was lower in both LRRK2 and PD than in controls. In LRRK2 patients a positive correlation was found between myocardial MIBG uptake and UPSIT scores, (R = 0.801, p < 0.001). In LRRK2 patients, MIBG cardiac uptake was less impaired than in PD; a positive correlation between MIBG cardiac uptake and UPSIT scores was observed. As MIBG cardiac reduced uptake and impaired odor identification are markers of LB pathology, this findings may represent neuropathological heterogeneity among LRRK2 patients.