Different saccadic profile in bulbar versus spinal-onset amyotrophic lateral sclerosis

Exploring oculomotor challenges in amyotrophic lateral sclerosis: a comprehensive review

Traditionally understood as a motor neuron disease, amyotrophic lateral sclerosis (ALS) is now recognized to involve broader neurodegenerative processes, including the oculomotor system. This narrative review summarizes current evidence on oculomotor dysfunction in ALS, with a focus on its relationship to disease-related motor and cognitive impairments. Specifically, the review examines key eye-tracking (ET) metrics, including saccades, smooth pursuit, and fixation, highlighting their potential to reflect both motor and extramotor degeneration. Notably, patients with bulbar-onset ALS exhibit more pronounced oculomotor impairments. By synthesizing findings on the connection between oculomotor dysfunction and cognitive decline, this review underscores the potential of ET as a noninvasive tool for assessing ALS progression. Oculomotor metrics, as part of a broader understanding of ALS's impact on multiple neural networks, may offer valuable insights to refine patient assessment and care strategies, particularly in advanced disease stages.

Lack of habituation in somatosensory cortex but not in visual cortex of ALS patients

OBJECTIVE

Amyotrophic lateral sclerosis (ALS) is a multisystem degenerative disease with extra-motor components. In ALS, there is also hyperexcitability of extra-motor areas. Habituation is defined as ''a response decrement" caused by repeated stimulations. Studies on evoked potential habituation can be conducted to detect cortical excitability. This study aimed to explore lack of habituation in non-motor cortical structures in ALS.

METHODS

Twenty-one ALS patients and 14 controls were enrolled. Recordings were obtained in 3 and 10 consecutive blocks (each containing 100 responses) during right median somatosensory evoked potential (SEP) and bilateral visual evoked potential (VEP), respectively. "Habituation" and "lack of habituation" were defined as the amount of increase or decrease in the average N20 or N75-P100 amplitude of the last blocks compared to the first blocks, respectively. Comparative analyses were performed between patient and control groups, as well as the first and last block within groups.

RESULTS

Paired sample t-test showed that in control group N20 peak amplitude of last blocks were significantly lower than first block values (p = 0.025) that indicate the physiological habituation as expected. On the other hand, there was not such a difference in ALS group (p = 0.239) which indicated lack of habituation.

CONCLUSIONS

Our study results suggest somatosensory hyperexcitability in line with cortical reorganization in ALS patients.

Annexin A11 mutations are associated with nuclear envelope dysfunction in vivo and in human tissues

Annexin A11 mutations are a rare cause of amyotrophic lateral sclerosis (ALS), wherein replicated protein variants P36R, G38R, D40G and D40Y are located in a small helix within the long, disordered N-terminus. To elucidate disease mechanisms, we characterized the phenotypes induced by a genetic loss-of-function and by misexpression of G38R and D40G in vivo. Loss of Annexin A11 results in a low-penetrant behavioural phenotype and aberrant axonal morphology in zebrafish homozygous knockout larvae, which is rescued by human wild-type Annexin A11. Both Annexin A11 knockout/down and ALS variants trigger nuclear dysfunction characterized by Lamin B2 mislocalization. The Lamin B2 signature also presented in anterior horn, spinal cord neurons from post-mortem ALS ± frontotemporal dementia patient tissue possessing G38R and D40G protein variants. These findings suggest mutant Annexin A11 acts as a dominant negative, revealing a potential early nucleopathy highlighting nuclear envelope abnormalities preceding behavioural abnormality in animal models.

[Oculomotor disorders in patients with amyotrophic lateral sclerosis]

Oculomotor disorders are not typical manifestations of amyotrophic lateral sclerosis (ALS). Occasionally, this disease is associated with vertical gaze paresis, presenting a distinct type as «ALS+progressive supranuclear palsy». Studies using eye-tracking methods have revealed a variety of subclinical oculomotor disorders in this disease. These disorders can manifest as changes in reflex and voluntary saccades, antisaccades, smooth tracking eye movements, and fixations. A significant association between oculomotor disorders and clinical manifestations of ALS was reported. The occurrence of oculomotor disorders indicates the involvement of broader neuroanatomical structures, including the prefrontal cortex and basal ganglia. The lack of consistency in the data from different studies and their limited number emphasize the need for further research in this area.

Exploring amyotrophic lateral sclerosis through the visual system: A systematic review

BACKGROUND AND PURPOSE

The human visual system relies on neural networks throughout the brain that are easily accessible for tests exploring eye structures and movements. Over the past two decades, investigations have been carried out on both afferent and efferent components of the visual system in people with amyotrophic lateral sclerosis (ALS). This approach might represent an innovative biomarker research strategy to better characterise the phenotypic variability of ALS. The purpose of this review was to determine whether exploring the visual system of patients with ALS (pwALS) is an effective strategy.

METHODS

The Medline and Web of science databases were searched for studies with terms relating to ALS and vision. Of 1146 references identified, 43 articles were included.

RESULTS

In this review article, both afferent and efferent components of the visual system were found to be impaired in pwALS in the absence of visual complaint, thereby contributing to the hypothesis that ALS is a multisystem disease with sensory involvement. Of note, some areas of the eye remain unexplored (i.e., tears, and retinal function using electroretinography).

CONCLUSIONS

According to the findings available in the literature, investigating the oculomotor system and exploring the ocular surface could represent two key promising strategies to identify new diagnostic biomarkers in pwALS. Further longitudinal studies are needed to identify relevant indicators of disease progression and response to therapeutic intervention.

Metabolomics of basal tears in amyotrophic lateral sclerosis: A cross-sectional study

PURPOSE

Amyotrophic lateral sclerosis (ALS) clinical variability, along with the lack of conclusive diagnostic instruments, result in average diagnosis delays of 9 months. This study aimed to assess whether metabolomic profiling of basal tears in ALS patients could act as a biological marker for diagnosing ALS, predicting prognosis, and discriminating between endophenotypes.

METHODS

A single-center prospective case-control study was conducted in France from September 2021 to March 2023 including patients with ALS according to the revised EI Escorial criteria. Two microliters of basal tears were collected using microcapillary glass tubes and analyzed with ultra-high performance liquid chromatography coupled with mass spectrometry. Both univariate and multivariate analyses were performed.

RESULTS

Twenty-five patients with ALS and 30 controls were included. No significant differences in metabolite levels were found between ALS and control groups (p > 0.05). The basal tear metabolome significantly discriminated bulbar and spinal forms of ALS based on 6 metabolites, among which 5 were decreased (aniline, trigonelline, caffeine, theophylline and methyl beta-D-galactoside) in the bulbar form and 1 was decreased in the spinal form (dodecanedioic acid).

CONCLUSION

This study represents the first prospective analysis of basal tear metabolomics in individuals with ALS. Despite the inability to distinguish between ALS patients and controls based on metabolic signatures, these findings could contribute to understanding the phenotypic diversity of ALS. Notably, distinct metabolic profiles were identified that differentiate between the bulbar and spinal forms of the disease.

Noradrenergic modulation of saccades in Parkinson's disease

Noradrenaline is a powerful modulator of cognitive processes, including action decisions underlying saccadic control. Changes in saccadic eye movements are common across neurodegenerative diseases of ageing, including Parkinson's disease. With growing interest in noradrenergic treatment potential for non-motor symptoms in Parkinson's disease, the temporal precision of oculomotor function is advantageous to assess the effects of this modulation. Here, we studied the effect of 40 mg atomoxetine, a noradrenaline reuptake inhibitor, in 19 people with idiopathic Parkinson's disease using a single dose, randomized double-blind, crossover, placebo-controlled design. Twenty-five healthy adult participants completed the assessments to provide normative data. Participants performed prosaccade and antisaccade tasks. The latency, velocity and accuracy of saccades, and resting pupil diameter, were measured. Increased pupil diameter on the drug confirmed its expected effect on the locus coeruleus ascending arousal system. Atomoxetine altered key aspects of saccade performance: prosaccade latencies were faster and the saccadic main sequence was normalized. These changes were accompanied by increased antisaccade error rates on the drug. Together, these findings suggest a shift in the speed-accuracy trade-off for visuomotor decisions in response to noradrenergic treatment. Our results provide new evidence to substantiate a role for noradrenergic modulation of saccades, and based on known circuitry, we advance the hypothesis that this reflects modulation at the level of the locus coeruleus-superior colliculus pathway. Given the potential for noradrenergic treatment of non-motor symptoms of Parkinson's disease and related conditions, the oculomotor system can support the assessment of cognitive effects without limb-motor confounds on task performance.

Memory-Guided Saccades in Subacute and Chronic Stroke: Secondary Data Analysis of the N-PEP-12 Clinical Study

BACKGROUND

Ischemic stroke (IS) often leads to cognitive and motor impairments. This study aimed to investigate whether Memory-Guided Saccade Tasks (MGSTs) could be used to assess cognitive function in stroke patients.

METHODS

A secondary data analysis was conducted on 62 individuals with supratentorial IS. Eye-tracking metrics from MGST were correlated with established neuropsychological assessments, including the Montreal Cognitive Assessment (MoCA) and Hospital Anxiety and Depression Scale (HADS).

RESULTS

Age correlated negatively with memory-guided saccade (MGS) accuracy (ρ = -0.274) and positively with late errors (ρ = 0.327). Higher Montreal Cognitive Assessment (MoCA) scores were associated with faster corrective saccades (ρ = 0.259). Increased anxiety (HADS-A) and depression (HADS-D) levels correlated with higher early error rates (ρ = 0.325 and ρ = 0.311, respectively). The Color Trails Test and Digit Span test performance also correlated with various MGS parameters.

CONCLUSIONS

While some correlations were found between cognitive measures and eye-tracking metrics, further research is needed to validate MGST as a tool for cognitive assessment in a more homogenous stroke population.

Oculomotor atypicalities in motor neurone disease: a systematic review

Introduction

Cognitive dysfunction is commonplace in Motor Neurone Disease (MND). However, due to the prominent motor symptoms in MND, assessing patients' cognitive function through traditional cognitive assessments, which oftentimes require motoric responses, may become increasingly challenging as the disease progresses. Oculomotor pathways are apparently resistant to pathological degeneration in MND. As such, abnormalities in oculomotor functions, largely driven by cognitive processes such as saccades and smooth pursuit eye movement, may be reflective of frontotemporal cognitive deficits in MND. Thus, saccadic and smooth pursuit eye movements may prove to be ideal mechanistic markers of cognitive function in MND.

Methods

To ascertain the utility of saccadic and smooth pursuit eye movements as markers of cognitive function in MND, this review summarizes the literature concerning saccadic and smooth pursuit eye movement task performance in people with MND.

Results and discussion

Of the 22 studies identified, noticeable patterns suggest that people with MND can be differentiated from controls based on antisaccade and smooth pursuit task performance, and thus the antisaccade task and smooth pursuit task may be potential candidates for markers of cognition in MND. However, further studies which ascertain the concordance between eye tracking measures and traditional measures of cognition are required before this assumption is extrapolated, and clinical recommendations are made.

Systematic review registration

https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=376620, identifier CRD42023376620.

Corneal nerves and amyotrophic lateral sclerosis: an in vivo corneal confocal imaging study

OBJECTIVES

Amyotrophic lateral sclerosis (ALS) is a severe motor neuron disorder. Diagnosis is challenging due to its clinical heterogeneity and the absence of definitive diagnostic tools, leading to delays averaging between 9.1 and 27 months. In vivo corneal confocal microscopy, assessing the sub-basal nerve plexus of the cornea, has been proposed as a potential biomarker for ALS. We aimed to determine whether the assessment of corneal nerves using in vivo confocal microscopy can serve as an imaging biomarker for ALS.

METHODS

A single-centre prospective case-control study was conducted in France from September 2021 to March 2023 including patients with ALS according to the revised EI Escorial criteria. The corneal sub-basal nerve plexus was analysed using in vivo confocal microscopy. An automated algorithm (ACCMetrics) was used to evaluate corneal parameters: nerve fibre density, nerve branch density, nerve fibre length, nerve fibre area, nerve total branch density, nerve fibre width, and nerve fractal dimension.

RESULTS

Twenty-two patients with ALS and 30 controls were included. No significant differences were found between ALS and control groups for all corneal parameters (p > 0.05). Corneal sensitivity did not differ between groups, and no correlation was identified between corneal nerve parameters and ALS disease duration, severity and rate of progression (p > 0.05).

CONCLUSIONS

The present study does not support the use of in vivo corneal confocal microscopy as an early diagnostic or prognostic tool for ALS. Further research, especially longitudinal investigations, is needed to understand any potential corneal innervation changes as ALS progresses.

Application and progress of advanced eye movement examinations in cognitive impairment

The worldwide incidence of cognitive impairment is escalating, yet no effective solutions for these afflictions have been discovered. Consequently, the importance of early identification and immediate intervention is heightened. Advanced eye movements-a form of voluntary eye movements that includes anti-saccades, memory-guided saccades, predictive saccades, pro-saccades and gap/overlap saccades, mediated by the cerebral cortex and subcortical pathways reflect cognitive levels and functions across different domains. In view of their objectivity, reproducibility, and non-invasive characteristics, advanced eye movement examination possesses significant prospective utility across a wide range of cognitive impairment. This paper extensively reviews various models associated with advanced eye movement examinations and their current applications in cognitive impairment such as Alzheimer's disease, Lewy body dementia and frontotemporal dementia. Advanced eye movement examination can serve as a biomarker for early screening diagnosis and research on cognitive impairment. In the future, combining advanced eye movement examination with neuropsychological scale assessment and other diagnostic methods may contribute to further early identification of these types of diseases.

Evidence based on Mendelian randomization and colocalization analysis strengthens causal relationships between structural changes in specific brain regions and risk of amyotrophic lateral sclerosis

Background

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by the degeneration of motor neurons in the brain and spinal cord with a poor prognosis. Previous studies have observed cognitive decline and changes in brain morphometry in ALS patients. However, it remains unclear whether the brain structural alterations contribute to the risk of ALS. In this study, we conducted a bidirectional two-sample Mendelian randomization (MR) and colocalization analysis to investigate this causal relationship.

Methods

Summary data of genome-wide association study were obtained for ALS and the brain structures, including surface area (SA), thickness and volume of subcortical structures. Inverse-variance weighted (IVW) method was used as the main estimate approach. Sensitivity analysis was conducted detect heterogeneity and pleiotropy. Colocalization analysis was performed to calculate the posterior probability of causal variation and identify the common genes.

Results

In the forward MR analysis, we found positive associations between the SA in four cortical regions (lingual, parahippocampal, pericalcarine, and middle temporal) and the risk of ALS. Additionally, decreased thickness in nine cortical regions (caudal anterior cingulate, frontal pole, fusiform, inferior temporal, lateral occipital, lateral orbitofrontal, pars orbitalis, pars triangularis, and pericalcarine) was significantly associated with a higher risk of ALS. In the reverse MR analysis, genetically predicted ALS was associated with reduced thickness in the bankssts and increased thickness in the caudal middle frontal, inferior parietal, medial orbitofrontal, and superior temporal regions. Colocalization analysis revealed the presence of shared causal variants between the two traits.

Conclusion

Our results suggest that altered brain morphometry in individuals with high ALS risk may be genetically mediated. The causal associations of widespread multifocal extra-motor atrophy in frontal and temporal lobes with ALS risk support the notion of a continuum between ALS and frontotemporal dementia. These findings enhance our understanding of the cortical structural patterns in ALS and shed light on potentially viable therapeutic targets.

Eye tracking assessment of Parkinson's disease: a clinical retrospective analysis

Parkinson's disease (PD) presents a significant clinical challenge due to its profound motor and cognitive impacts. Early diagnosis is crucial for implementing effective, stage-based treatment strategies. Recently, eye-tracking technology has emerged as a promising tool for the non-invasive diagnosis and monitoring of various neurological disorders, including PD. This retrospective study analyzed eye-tracking parameters, specifically visually-guided saccades (VGS), in PD patients within a clinical setting. We reviewed eye-tracking data from 62 PD patients, focusing on eye movement performance in horizontal and vertical VGS tasks. Our findings revealed significant correlations between demographic profiles, Mini-Mental State Examination (MMSE) scores, pattern recognition, and spatial working memory tests with saccadic performance in PD patients. Despite the retrospective nature of the study, our results support the potential of eye-tracking technology as a valuable diagnostic tool in PD assessment and monitoring. Future research should prioritize longitudinal studies and more comprehensive assessments to further understand and enhance the clinical application of eye-tracking in PD.

Saccadic oscillations as a biomarker of clinical symptoms in amyotrophic lateral sclerosis

BACKGROUND

Among eye movements in amyotrophic lateral sclerosis (ALS), we identified the characteristics of square-wave jerks (SWJs) seen during times without visual fixation (VF) and analyzed their relationships with clinical parameters.

MATERIALS AND METHODS

Clinical symptoms were evaluated and eye movements were tested using electronystagmography in 15 patients with ALS (10 men, 5 women; mean age, 66.9 ± 10.5 years). SWJs with and without VF were recorded, and their characteristics were identified. Relationships between each SWJ parameter and clinical symptoms were evaluated. Results were compared with eye movement data from 18 healthy individuals.

RESULTS

The frequency of SWJs without VF was significantly higher in the ALS group than in the healthy group (P < 0.001). When the condition was changed from VF to no-VF in the ALS group, the frequency of SWJs was significantly higher in healthy subjects (P = 0.004). A positive correlation was seen between frequency of SWJs and percentage predicted forced vital capacity (%FVC) (R = 0.546, P = 0.035).

CONCLUSION

The frequency of SWJs was higher with VF in healthy people, and was suppressed without VF. In contrast, the frequency of SWJs was not suppressed without VF in ALS patients. This suggests that SWJs without VF have some clinical significance in ALS patients. Moreover, a relationship was noted between the parameters of SWJs without VF in ALS patients and results of pulmonary function tests, suggesting that SWJs during times without VF may offer a clinical parameter of ALS.