Impairment in Respiratory Function Contributes to Olfactory Impairment in Amyotrophic Lateral Sclerosis

Smell loss is associated with cognitive impairment in amyotrophic lateral sclerosis patients

BACKGROUND

Smell loss significantly impacts the quality of life in patients. However, there is limited research on smell loss in individuals with amyotrophic lateral sclerosis (ALS), and the correlation between smell loss and cognitive impairment is unclear. This study aimed to investigate the correlation between smell loss and cognition impairment in ALS patients.

METHODS

The study included 216 ALS patients. The Edinburgh Cognitive and Behavioural ALS Screen (ECAS) and smell identification test specifically for the Chinese population (CSIT) were administered to evaluate participants' cognitive and olfactory function, respectively.

RESULTS

After covarying for age, sex, BMI, education level, degree of hunger, dietary bias, eagerness for food, stress, smoking status, alcohol consumption, and upper respiratory tract infection (URTI) or rhinitis, CSIT scores were significantly correlated with ECAS scores (r = 0.162, p = 0.028), especially the ALS-specific scores (r = 0.158, p = 0.031). Even after excluding patients with URTI or rhinitis, the results were similar. CSIT scores were significantly correlated with ECAS scores (r = 0.224, p = 0.011), especially the ALS-specific scores (r = 0.205, p = 0.019).

CONCLUSION

In patients with ALS, smell loss is significantly correlated with cognitive impairment, particularly frontotemporal dysfunction. Cognitive dysfunction may lead to worse olfactory performance in ALS patients.

The anterior olfactory nucleus revisited - an emerging role for neuropathological conditions?

Olfaction is an important sensory modality for many species and greatly influences animal and human behavior. Still, much about olfactory perception remains unknown. The anterior olfactory nucleus is one of the brain's central early olfactory processing areas. Located directly posterior to the olfactory bulb in the olfactory peduncle with extensive in- and output connections and unique cellular composition, it connects olfactory processing centers of the left and right hemispheres. Almost 20 years have passed since the last comprehensive review on the anterior olfactory nucleus has been published and significant advances regarding its anatomy, function, and pathophysiology have been made in the meantime. Here we briefly summarize previous knowledge on the anterior olfactory nucleus, give detailed insights into the progress that has been made in recent years, and map out its emerging importance in translational research of neurological diseases.

Sensory Involvement in Amyotrophic Lateral Sclerosis

Although amyotrophic lateral sclerosis (ALS) is pre-eminently a motor disease, the existence of non-motor manifestations, including sensory involvement, has been described in the last few years. Although from a clinical perspective, sensory symptoms are overshadowed by their motor manifestations, this does not mean that their pathological significance is not relevant. In this review, we have made an extensive description of the involvement of sensory and autonomic systems described to date in ALS, from clinical, neurophysiological, neuroimaging, neuropathological, functional, and molecular perspectives.

Non-Motor Features of Amyotrophic Lateral Sclerosis: A Clinic-based Study

Introduction:

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder of motor neurons. Spread of pathology to other brain areas leads to development of non-motor symptoms (NMSs). These usually remain undiagnosed because of overwhelming motor problem and are responsible for significant distress to the patient. Our objective was to explore the burden of various NMSs of patients with ALS, compare between limb-onset and bulbar-onset patients, and to correlate with severity and duration of disease.

Methods:

Fifty patients with ALS diagnosed according to revised El Escorial Criteria and 50 healthy controls were included in this study. They were assessed with NMS Questionnaire, Beck's Depression Inventory, Center for Neurologic Study-Lability Scale, Drooling Frequency and Severity Scale, Epworth Sleepiness scale, Bengali Mental State Examination, and Frontal Assessment Battery and relevant statistical analyses were carried out.

Results:

The patients with ALS had significantly increased prevalence of almost all NMSs compared to controls. There was also significant increase in depression, suicidal ideation, pseudobulbar affect, and daytime sleepiness in patients with ALS. The bulbar onset subgroup had significantly increased daytime drooling, dysphagia, nausea and vomiting, whereas the limb onset subgroup reported increased frequency of leg swelling. Executive dysfunction was detected in 24% of patients with ALS and 9.8% had mild cognitive impairment. Weight loss, frequency of falling, insomnia, unpleasant nocturnal leg sensations, difficulty having sex, depression, and cognitive impairment increased significantly with an increase in severity of the disease.

Conclusion:

NMSs were significantly more prevalent in patients with ALS. Some NMSs worsened with advancement of the disease.

Clinicoradiological features in amyotrophic lateral sclerosis patients with olfactory dysfunction

Objective: Amyotrophic lateral sclerosis (ALS) is an adult-onset neurodegenerative disorder characterized by motor neuron involvement. Although olfactory dysfunction has been described in ALS, clinicoradiological features associated with the olfactory dysfunction remain poorly understood. Methods: We enrolled 30 patients with ALS and age- and sex-matched 53 healthy controls (HCs). All participants underwent the odor stick identification test for Japanese (OSIT-J) and clinical assessments, including disease duration, ALSFRS-R, site of onset, forced vital capacity, and cognitive examinations that reflected the general, executive, memory and language function. We investigated the associations between OSIT-J score and clinical features and examined atrophic changes by voxel-based morphometry (VBM) analysis to MRI. Results: The OSIT-J score was significantly lower in ALS patients than HCs (6.9 ± 3.2 vs. 9.8 ± 1.9, p < 0.001). In ALS, there were significant relationships between OSIT-J score and age at examination, frontal assessment battery, word fluencies, digit span forward, and ADAS-Jcog recognition, but not education, disease type, duration, ALSFRS-R and, %VC. Multiple regression analysis with stepwise method showed the only ADAS-Jcog recognition substantially predicted OSIT-J score. VBM analysis with age, sex, total intracranial volume, and ADAS-Jcog recognition as covariates showed OSIT-J scores were substantially correlated with atrophic changes of left orbital cortex consisting of gyrus rectus and medial orbital gyrus and right hippocampus in ALS. Conclusion: ALS patients could show substantial olfactory dysfunction in association with orbital cortex and hippocampus involvements. The olfactory examination could be a useful marker for screening of frontotemporal alteration in ALS.

Amyotrophic Lateral Sclerosis Is Accompanied by Protein Derangements in the Olfactory Bulb-Tract Axis

Amyotrophic lateral sclerosis (ALS) is a fatal disease characterized by progressive muscle paralysis due to the degeneration of upper and lower motor neurons. Recent studies point out an involvement of the non-motor axis during disease progression. Despite smell impairment being considered a potential non-motor finding in ALS, the pathobiochemistry at the olfactory level remains unknown. Here, we applied an olfactory quantitative proteotyping approach to analyze the magnitude of the olfactory bulb (OB) proteostatic imbalance in ALS subjects (n = 12) with respect to controls (n = 8). Around 3% of the quantified OB proteome was differentially expressed, pinpointing aberrant protein expression involved in vesicle-mediated transport, macroautophagy, axon development and gliogenesis in ALS subjects. The overproduction of olfactory marker protein (OMP) points out an imbalance in the olfactory signal transduction in ALS. Accompanying the specific overexpression of glial fibrillary acidic protein (GFAP) and Bcl-xL in the olfactory tract (OT), a tangled disruption of signaling routes was evidenced across the OB–OT axis in ALS. In particular, the OB survival signaling dynamics clearly differ between ALS and frontotemporal lobar degeneration (FTLD), two faces of TDP-43 proteinopathy. To the best of our knowledge, this is the first report on high-throughput molecular characterization of the olfactory proteostasis in ALS.

Loss of Olfactory Function-Early Indicator for Covid-19, Other Viral Infections and Neurodegenerative Disorders

The loss of the senses of smell (anosmia) and taste (ageusia) are rather common disorders, affecting up to 20% of the adult population. Yet, this condition has not received the attention it deserves, most probably because per se such a disorder is not life threatening. However, loss of olfactory function significantly reduces the quality of life of the affected patients, leading to dislike in food and insufficient, exaggerated or unbalanced food intake, unintentional exposure to toxins such as household gas, social isolation, depression, and an overall insecurity. Not only is olfactory dysfunction rather prevalent in the healthy population, it is, in many instances, also a correlate or an early indicator of a panoply of diseases. Importantly, olfactory dysfunction is linked to the two most prominent neurodegenerative disorders, Parkinson's disease and Alzheimer's disease. Anosmia and hyposmia (reduced sense of smell) affect a majority of patients years before the onset of cognitive or motor symptoms, establishing olfactory dysfunction as early biomarker that can enable earlier diagnosis and preventative treatments. In the current health crisis caused by SARS-CoV2, anosmia and dysgeusia as early-onset symptoms in virus-positive patients may prove to be highly relevant and crucial for pre-symptomatic Covid-19 detection from a public health perspective, preceding by days the more classical respiratory tract symptoms such as cough, tightness of the chest or fever. Thus, the olfactory system seems to be at the frontline of pathologic assault, be it through pathogens or insults that can lead to or at least associate with neurodegeneration. The aim of this review is to assemble current knowledge from different medical fields that all share a common denominator, olfactory/gustatory dysfunction, and to distill overarching etiologies and disease progression mechanisms.

Contribution of ambient noise and hyperbaric atmosphere to olfactory and gustatory function

Introduction

Taste and smell are important for occupational performance and quality of life. Previous studies suggested that the function of these senses might be influenced by ambient pressure and noise. This knowledge would be helpful for divers, submarine crews, or mine workers. The present study aimed to investigate the effects of noise and hyperbaric pressure on olfactory and gustatory functions.

Methods

This prospective controlled study included 16 healthy male divers. Inside a hyperbaric chamber, participants performed olfactory and gustatory function tests at sea level pressure and at 2 bar pressure. The olfaction threshold, and the discrimination and identification of odorants were measured with validated ´Sniffin sticks´. Taste identification and the gustation threshold scores were examined with validated filter paper strips. Tests were performed under two conditions: noise reduction (silence) and white noise stimulation presented at 70 dB sound pressure level.

Results

The results showed that normobaric and hyperbaric ambient pressures did not significantly affect olfactory or gustatory function. Moreover, noise had no relevant impact on taste or odor sensation. The odor identification score was not influenced in hyperbaric conditions, and the odor threshold score was not influenced by ambient noise or both barometric conditions. The only taste modality affected by hyperbaric conditions was the sensitivity to salty taste, but it was not significant.

Conclusion

We concluded that hyperbaric and noisy environments have no influence on gustatory and olfactory function. From a practical point of view, the influence of pressure in moderate hyperbaric occupations should be negligible.

Olfactory and gustatory dysfunctions in 100 patients hospitalized for COVID-19: sex differences and recovery time in real-life

Purpose

COVID-19 displays a variety of clinical manifestations; in pauci-symptomatic patients olfactory (OD) and gustatory dysfunctions (GD) may represent the first or only symptom. This topic is currently arousing great interest, and a growing number of papers are being published. Aim of this study is to investigate the timing of recovery from OD and GD in a real-life population hospitalized for COVID-19.

Methods

We followed up by a phone interview the first 100 patients discharged a month earlier from three Italian non-intensive care wards.

Results

All 100 patients were Caucasian, mean age was 65 years, 60% were males. Forty-two patients (mean age 63 years) experienced subjective chemosensory dysfunctions (29 OD and 41 GD): the male/female ratio was 2:1; 83% reported a complete or near complete recovery at follow-up. The recovery rate was not significantly different between males and females. The mean duration of OD and GD was 18 and 16 days, respectively. The mean recovery time from OD or GD resulted significantly longer for females than for males (26 vs 14 days, P = 0.009). Among the 42 symptomatic, the mean age of males was significantly higher than that of females (66 vs 57 years, P = 0.04), while the opposite was observed in the 58 asymptomatic patients (60 vs 73 years, P = 0.0018).

Conclusions

Recovery from OD or GD was rapid, occurring within 4 weeks in most patients. Chemosensory dysfunctions in women was less frequent, but longer lasting. The value of our study is its focus on a population of hospitalized patients significantly older than those previously described, and the additional data on gender differences.

Olfactory Performance as an Indicator for Protective Treatment Effects in an Animal Model of Neurodegeneration

Background: Neurodegenerative diseases are often accompanied by olfactory deficits. Here we use a rare neurovisceral lipid storage disorder, Niemann–Pick disease C1 (NPC1), to illustrate disease-specific dynamics of olfactory dysfunction and its reaction upon therapy. Previous findings in a transgenic mouse model (NPC1^-/-) showed severe morphological and electrophysiological alterations of the olfactory epithelium (OE) and the olfactory bulb (OB) that ameliorated under therapy with combined 2-hydroxypropyl-ß-cyclodextrin (HPßCD)/allopregnanolone/miglustat or HPßCD alone.

Methods: A buried pellet test was conducted to assess olfactory performance. qPCR for olfactory key markers and several olfactory receptors was applied to determine if their expression was changed under treatment conditions. In order to investigate the cell dynamics of the OB, we determined proliferative and apoptotic activities using a bromodeoxyuridine (BrdU) protocol and caspase-3 (cas-3) activity. Further, we performed immunohistochemistry and western blotting for microglia (Iba1), astroglia (GFAP) and tyrosine hydroxylase (TH).

Results: The buried pellet test revealed a significant olfactory deterioration in NPC1^-/- mice, which reverted to normal levels after treatment. At the OE level, mRNA for olfactory markers showed no changes; the mRNA level of classical olfactory receptor (ORs) was unaltered, that of unique ORs was reduced. In the OB of untreated NPC1^-/- mice, BrdU and cas-3 data showed increased proliferation and apoptotic activity, respectively. At the protein level, Iba1 and GFAP in the OB indicated increased microgliosis and astrogliosis, which was prevented by treatment.

Conclusion: Due to the unique plasticity especially of peripheral olfactory components the results show a successful treatment in NPC1 condition with respect to normalization of olfaction. Unchanged mRNA levels for olfactory marker protein and distinct olfactory receptors indicate no effects in the OE in NPC1^-/- mice. Olfactory deficits are thus likely due to central deficits at the level of the OB. Further studies are needed to examine if olfactory performance can also be changed at a later onset and interrupted treatment of the disease. Taken together, our results demonstrate that olfactory testing in patients with NPC1 may be successfully used as a biomarker during the monitoring of the treatment.

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.