Neuroimaging Endpoints in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative, clinically heterogeneous syndrome pathologically overlapping with frontotemporal dementia. To date, therapeutic trials in animal models have not been able to predict treatment response in humans, and the revised ALS Functional Rating Scale, which is based on coarse disability measures, remains the gold-standard measure of disease progression. Advances in neuroimaging have enabled mapping of functional, structural, and molecular aspects of ALS pathology, and these objective measures may be uniquely sensitive to the detection of propagation of pathology in vivo. Abnormalities are detectable before clinical symptoms develop, offering the potential for neuroprotective intervention in familial cases. Although promising neuroimaging biomarker candidates for diagnosis, prognosis, and disease progression have emerged, these have been from the study of necessarily select patient cohorts identified in specialized referral centers. Further multicenter research is now needed to establish their validity as therapeutic outcome measures.

Motor neuron disease: biomarker development for an expanding cerebral syndrome

Descriptions of motor neuron disease (MND) documented more than a century ago remain instantly recognisable to the physician. The muscle weakness, typically with signs of upper and lower motor neuron dysfunction, is uniquely relentless. Over the last 30 years, a wider cerebral pathology has emerged, despite the lack of overt cognitive impairment in the majority of patients. From the initial linkage of a small number of cases to mutations in SOD1, diverse cellular pathways have been implicated in pathogenesis. An increasingly complex clinical heterogeneity has emerged around a significant variability in survival. Defining a cellular signature of aggregated TDP-43 common to nearly all MND and a large proportion of frontotemporal dementia (FTD), has placed MND alongside more traditional cerebral neurodegeneration. With new genetic causes, most notably a hexanucleotide expansion in C9orf72 associated with both MND and FTD, the development of biomarkers against which to test therapeutic candidates is a priority.

Differential Impairment of Thalamocortical Structural Connectivity in Amyotrophic Lateral Sclerosis

AIMS

The thalamus is a major relay station that modulates input from many cortical areas and a filter for sensory input and is involved in the pathophysiology of amyotrophic lateral sclerosis (ALS). However, it still remains unclear whether all thalamocortical networks are affected or whether there is selective vulnerability. In this study, we aimed to study the selective vulnerability of different thalamocortical structural connections in ALS and to test the hypothesis of a specific impairment in motor-related thalamocortical connectivity.

METHODS

Diffusion tensor imaging (DTI) tractography was used to identify thalamocortical structural pathways in 38 individuals with ALS and 35 gender/age-matched control subjects. Thalami of both groups were parcellated into subregions based on local patterns of thalamocortical connectivity. DTI measures of these distinct thalamocortical connections were derived and compared between groups.

RESULTS

The analysis of probabilistic tractography showed that the structural connectivity between bilateral pre/primary motor cortices and associated thalamic subregions was specifically impaired in patients with ALS, while the other thalamocortical connections remained relatively intact. In addition, fractional anisotropy values of the impaired thalamocortical motor pathway were inversely correlated with the disease duration.

CONCLUSION

Our findings provide direct evidence for selective impairment of the thalamocortical structural connectivity in ALS.

The corticospinal tract profile in amyotrophic lateral sclerosis

This work evaluates the potential in diagnostic application of a new advanced neuroimaging method, which delineates the profile of tissue properties along the corticospinal tract (CST) in amyotrophic lateral sclerosis (ALS), by means of diffusion tensor imaging (DTI). Twenty-four ALS patients and twenty-four demographically matched healthy subjects were enrolled in this study. The Automated Fiber Quantification (AFQ), a tool for the automatic reconstruction of white matter tract profiles, based on a deterministic tractography algorithm to automatically identify the CST and quantify its diffusion properties, was used. At a group level, the highest non-overlapping DTI-related differences were detected in the cerebral peduncle, posterior limb of the internal capsule, and primary motor cortex. Fractional anisotropy (FA) decrease and mean diffusivity (MD) and radial diffusivity (RD) increases were detected when comparing ALS patients to controls. The machine learning approach used to assess the clinical utility of this DTI tool revealed that, by combining all DTI metrics measured along tract between the cerebral peduncle and the corona radiata, a mean 5-fold cross validation accuracy of 80% was reached in discriminating ALS from controls. Our study provides a useful new neuroimaging tool to characterize ALS-related neurodegenerative processes by means of CST profile. We demonstrated that specific microstructural changes in the upper part of the brainstem might be considered as a valid biomarker. With further validations this method has the potential to be considered a promising step toward the diagnostic utility of DTI measures in ALS. Hum Brain Mapp 38:727-739, 2017. © 2016 Wiley Periodicals, Inc.

Corticoefferent pathways in pure lower motor neuron disease: a diffusion tensor imaging study

Criteria for assessing upper motor neuron pathology in lower motor neuron disease (LMND) still remain major issues in clinical diagnosis. This study was designed to investigate patients with the clinical diagnosis of adult pure LMND by use of whole brain based diffusion tensor imaging (DTI) to delineate alterations of corticoefferent pathways in vivo. Comparison of fractional anisotropy (FA) maps was performed by whole brain-based spatial statistics for 37 LMND patients vs. 53 matched controls to detect white matter structural alterations. LMND patients were clinically differentiated in fast and slow progressors. Furthermore, tract specific alterations were investigated by fiber tracking techniques according to the staging hypothesis for amyotrophic lateral sclerosis (ALS). The analysis of white matter structural connectivity demonstrated widespread and characteristic patterns of alterations in patients with LMND, predominantly along the corticospinal tract (CST), with multiple clusters of regional FA reductions in the motor system at p < 0.05 (corrected for multiple comparisons). Fast progressing LMND showed substantial CST involvement, while slow progressors showed less CST alterations. In the tract-specific analysis according to the ALS-staging pattern as suggested by Braak, fast progressing LMND showed significant alterations of ALS-related tract systems beyond the CST compared to slow progressors and controls. In clinically pure LMND patients, the involvement of corticoefferent fibers was demonstrated, in particular along the CST, supporting the hypothesis that LMND is a phenotypical variant of ALS. This finding suggests to treat these patients like ALS, including the opportunity to participate in clinical trials.

Progressive Muscular Atrophy

Progressive muscular atrophy (PMA) is a rare, sporadic, adult-onset motor neuron disease, clinically characterized by isolated lower motor neuron features; however, clinically evident upper motor neuron signs may emerge in some patients. Subclinical upper motor neuron involvement is identified pathologically, radiologically, and neurophysiologically in a substantial number of patients with PMA. Patients with subclinical upper motor neuron involvement do not fulfill the revised El Escorial criteria to participate in amyotrophic lateral sclerosis clinical trials. Intravenous immunoglobulin therapy is only marginally beneficial in a small subgroup of patients with lower motor neuron syndrome without conduction block.

Non-Motor Symptoms in Patients Suffering from Motor Neuron Diseases

Background

The recently postulated “disease spreading hypothesis” has gained much attention, especially for Parkinson’s disease (PD). The various non-motor symptoms (NMS) in neurodegenerative diseases would be much better explained by this hypothesis than by the degeneration of disease-specific cell populations. Motor neuron disease (MND) is primarily known as a group of diseases with a selective loss of motor function. However, recent evidence suggests disease spreading into non-motor brain regions also in MND. The aim of this study was to comprehensively detect NMS in patients suffering from MND.

Methods

We used a self-rating questionnaire including 30 different items of gastrointestinal, autonomic, neuropsychiatric, and sleep complaints [NMS questionnaire (NMSQuest)], which is an established tool in PD patients. 90 MND patients were included and compared to 96 controls.

Results

In total, MND patients reported significantly higher NMS scores (median: 7 points) in comparison to controls (median: 4 points). Dribbling, impaired taste/smelling, impaired swallowing, weight loss, loss of interest, sad/blues, falling, and insomnia were significantly more prevalent in MND patients compared to controls. Interestingly, excessive sweating was more reported in the MND group. Correlation analysis revealed an increase of total NMS score with disease progression.

Conclusion

NMS in MND patients seemed to increase with disease progression, which would fit with the recently postulated “disease spreading hypothesis.” The total NMS score in the MND group significantly exceeded the score for the control group, but only 8 of the 30 single complaints of the NMSQuest were significantly more often reported by MND patients. Dribbling, impaired swallowing, weight loss, and falling could primarily be connected to motor neuron degeneration and declared as motor symptoms in MND.

Structural and diffusion imaging versus clinical assessment to monitor amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis is a progressive neurodegenerative disease that affects upper and lower motor neurons. Observational and intervention studies can be tracked using clinical measures such as the revised Amyotrophic Lateral Sclerosis Functional Rating Scale (ALSFRS-R) but for a complete understanding of disease progression, objective in vivo biomarkers of both central and peripheral motor pathway pathology are highly desirable. The aim of this study was to determine the utility of structural and diffusion imaging as central nervous system biomarkers compared to the standard clinical measure, ALSFRS-R, to track longitudinal evolution using three time-point measurements. N = 34 patients with ALS were scanned and clinically assessed three times at a mean of three month time intervals. The MRI biomarkers were structural T1-weighted volumes for cortical thickness measurement as well as deep grey matter volumetry, voxel-based morphometry and diffusion tensor imaging (DTI). Cortical thickness focused specifically on the precentral gyrus while quantitative DTI biomarkers focused on the corticospinal tracts. The evolution of imaging biomarkers and ALSFRS-R scores over time were analysed using a mixed effects model that accounted for the scanning interval as a fixed effect variable, and, the initial measurements and time from onset as random variables. The mixed effects model showed a significant decrease in the ALSFRS-R score, (p < 0.0001, and an annual rate of change (AROC) of − 7.3 points). Similarly, fractional anisotropy of the corticospinal tract showed a significant decrease (p = 0.009, AROC = − 0.0066) that, in turn, was driven by a significant increase in radial diffusivity combined with a trend to decrease in axial diffusivity. No significant change in cortical thickness of the precentral gyrus was found (p > 0.5). In addition, deep grey matter volumetry and voxel-based morphometry also identified no significant changes. Furthermore, the availability of three time points was able to indicate that there was a linear progression in both clinical and fractional anisotropy measures adding to the validity of these results. The results indicate that DTI is clearly a superior imaging marker compared to atrophy for tracking the evolution of the disease and can act as a central nervous biomarker in longitudinal studies. It remains, however, less sensitive than the ALSFRS-R score for monitoring decline over time.

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Three time points were used for the first time to assess imaging biomarkers in ALS.

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Fractional anisotropy of the corticospinal tract showed linear decline.

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No atrophy measure was useful to track change.

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The ALSFRS-R clinical scale remains more sensitive than imaging biomarkers.

Brain MR Imaging in Patients with Lower Motor Neuron-Predominant Disease

Purpose To investigate the patterns of cortical thinning and white matter tract damage in patients with lower motor neuron (LMN)-predominant disease compared with healthy control subjects and those with classic amyotrophic lateral sclerosis (ALS) and to evaluate the relationship between brain structural changes and clinical and cognitive features in these patients. Materials and Methods This study was approved by the local ethical committee, and written informed consent was obtained from all subjects before enrollment. Twenty-eight patients with LMN-predominant disease were compared with 55 patients with ALS and 56 healthy control subjects. Patients underwent a clinical and neuropsychological assessment and T1-weighted and diffusion-tensor magnetic resonance (MR) imaging. Surface-based morphometry was used to assess cortical thickness. Tract-based spatial statistics and tractography were used to study white matter tract damage. Results Patients with LMN-predominant disease did not show differences compared with healthy control subjects in cortical thickness and diffusion-tensor MR imaging metrics. Patients with ALS showed cortical thinning of the motor-related cortices and a distributed involvement of the prefrontal, temporal, and parietal gyri (P < .05, false discovery rate corrected). Patients with ALS also showed white matter damage along motor and extramotor tracts compared with control subjects and patients with LMN-predominant disease (tract-based spatial statistics: P < .05, family-wise error corrected; tractography: P values < .001 to .05, false discovery rate corrected). In patients with LMN-predominant disease, cognitive deficits correlated with alterations in diffusivity in the left cingulum (r = -0.66, P = .01) and superior longitudinal fasciculus (r = -0.65, P = .05). Conclusion Motor and extramotor cortical thinning and diffusion-tensor MR imaging alterations were specific for motor neuron disease phenotypes, with clinically overt upper motor neuron involvement. However, the lack of significant differences in cortical thickness between subjects with LMN-predominant disease and those with ALS and cognitive deficits associated with alterations in diffusivity in patients with LMN-predominant disease suggest that investigating brain structural and microstructural MR imaging features may provide markers of central nervous system damage in patients with rare motor neuron disease. (©) RSNA, 2016 Online supplemental material is available for this article.

Structural brain correlates of cognitive and behavioral impairment in MND

OBJECTIVE

To assess the structural correlates of cognitive and behavioral impairment in motor neuron diseases (MND) using multimodal MRI.

METHODS

One hundred one patients with sporadic MND (56 classic amyotrophic lateral sclerosis, 31 upper motor neuron phenotype, and 14 lower motor neuron phenotype) and 51 controls were enrolled. Patients were classified into MND with a pure motor syndrome (MND-motor) and with cognitive/behavioral symptoms (MND-plus). Cortical thickness measures and diffusion tensor (DT) metrics of white matter (WM) tracts were assessed. A random forest approach was used to explore the independent role of cortical and WM abnormalities in explaining major cognitive and behavioral symptoms.

RESULTS

There were 48 MND-motor and 53 MND-plus patients. Relative to controls, both patient groups showed a distributed cortical thinning of the bilateral precentral gyrus, insular and cingulate cortices, and frontotemporal regions. In all regions, there was a trend toward a more severe involvement in MND-plus cases, particularly in the temporal lobes. Both patient groups showed damage to the motor callosal fibers, which was more severe in MND-plus. MND-plus patients also showed a more severe involvement of the extra-motor WM tracts. The best predictors of executive and non-executive deficits and behavioral symptoms in MND were diffusivity abnormalities of the corpus callosum and frontotemporal tracts, including the uncinate, cingulum, and superior longitudinal fasciculi.

CONCLUSIONS

Cortical thinning and WM degeneration are highly associated with neuropsychological and behavioral symptoms in patients with MND. DT MRI metrics seem to be the most sensitive markers of extra-motor deficits within the MND spectrum.

Presymptomatic and longitudinal neuroimaging in neurodegeneration--from snapshots to motion picture: a systematic review

BACKGROUND

Recent quantitative neuroimaging studies have been successful in capturing phenotype and genotype-specific changes in dementia syndromes, amyotrophic lateral sclerosis, Parkinson's disease and other neurodegenerative conditions. However, the majority of imaging studies are cross-sectional, despite the obvious superiority of longitudinal study designs in characterising disease trajectories, response to therapy, progression rates and evaluating the presymptomatic phase of neurodegenerative conditions.

OBJECTIVES

The aim of this work is to perform a systematic review of longitudinal imaging initiatives in neurodegeneration focusing on methodology, optimal statistical models, follow-up intervals, attrition rates, primary study outcomes and presymptomatic studies.

METHODS

Longitudinal imaging studies were identified from 'PubMed' and reviewed from 1990 to 2014. The search terms 'longitudinal', 'MRI', 'presymptomatic' and 'imaging' were utilised in combination with one of the following degenerative conditions; Alzheimer's disease, amyotrophic lateral sclerosis/motor neuron disease, frontotemporal dementia, Huntington's disease, multiple sclerosis, Parkinson's disease, ataxia, HIV, alcohol abuse/dependence.

RESULTS

A total of 423 longitudinal imaging papers and 103 genotype-based presymptomatic studies were identified and systematically reviewed. Imaging techniques, follow-up intervals and attrition rates showed significant variation depending on the primary diagnosis. Commonly used statistical models included analysis of annualised percentage change, mixed and random effect models, and non-linear cumulative models with acceleration-deceleration components.

DISCUSSION AND CONCLUSIONS

Although longitudinal imaging studies have the potential to provide crucial insights into the presymptomatic phase and natural trajectory of neurodegenerative processes a standardised design is required to enable meaningful data interpretation.

Primary Lateral Sclerosis

Primary lateral sclerosis is characterized by insidious onset of progressive upper motor neuron dysfunction in the absence of clinical signs of lower motor neuron involvement. Patients experience stiffness; decreased balance and coordination; mild weakness; and, if the bulbar region is affected, difficulty speaking and swallowing, and emotional lability. The diagnosis is made based on clinical history, typical examination findings, and diagnostic testing negative for other causes of upper motor neuron dysfunction. Electromyogram is normal, or only shows mild neurogenic findings in a few muscles, not meeting El Escorial criteria. Treatment is largely supportive.

Structural hallmarks of amyotrophic lateral sclerosis progression revealed by probabilistic fiber tractography

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by progressive limb and/or bulbar muscular weakness and atrophy. Although ALS-related alterations of motor and extra-motor neuronal networks have repeatedly been reported, their temporal dynamics during disease progression are not well understood. Recently, we reported a decline of motor system activity and a concurrent increase of hippocampal novelty-evoked modulations across 3 months of ALS progression. To address whether these functional changes are associated with structural ones, the current study employed probabilistic fiber tractography on diffusion tensor imaging (DTI) data using a longitudinal design. Therein, motor network integrity was assessed by DTI-based tracking of the intracranial corticospinal tract, while connectivity estimates of occipito-temporal tracts (between visual and entorhinal, perirhinal or parahippocampal cortices) served to assess structural changes that could be related to the increased novelty-evoked hippocampal activity across time described previously. Complementing these previous functional observations, the current data revealed an ALS-related decrease in corticospinal tract structural connectivity compared to controls, while in contrast, visuo-perirhinal connectivity was relatively increased in the patient group. Importantly, beyond these between-group differences, a rise in the patients' occipito-temporal tract strengths occurred across a 3-month interval, while at the same time no changes in corticospinal tract connectivity were observed. In line with previously identified functional alterations, the dynamics of these structural changes suggest that the affection of motor- and memory-related networks in ALS emerges at distinct disease stages: while motor network degeneration starts primarily during early (supposedly pre-symptomatic) phases, the hippocampal/medial temporal lobe dysfunctions arise at later stages of the disease.

Detecting statistically significant differences in quantitative MRI experiments, applied to diffusion tensor imaging

In this work we present a framework for reliably detecting significant differences in quantitative magnetic resonance imaging and evaluate it with diffusion tensor imaging (DTI) experiments. As part of this framework we propose a new spatially regularized maximum likelihood estimator that simultaneously estimates the quantitative parameters and the spatially-smoothly-varying noise level from the acquisitions. The noise level estimation method does not require repeated acquisitions. We show that the amount of regularization in this method can be set a priori to achieve a desired coefficient of variation of the estimated noise level. The noise level estimate allows the construction of a Cramér-Rao-lower-bound based test statistic that reliably assesses the significance of differences between voxels within a scan or across different scans. We show that the regularized noise level estimate improves upon existing methods and results in a substantially increased precision of the uncertainty estimates of the DTI parameters. It enables correct specification of the null distribution of the test statistic and with it the test statistic obtains the highest sensitivity and specificity. The source code of the estimation framework, test statistic and experiment scripts are made available to the community.

Diffusion-MRI in neurodegenerative disorders

The ability to image the whole brain through ever more subtle and specific methods/contrasts has come to play a key role in understanding the basis of brain abnormalities in several diseases. In magnetic resonance imaging (MRI), "diffusion" (i.e. the random, thermally-induced displacements of water molecules over time) represents an extraordinarily sensitive contrast mechanism, and the exquisite structural detail it affords has proven useful in a vast number of clinical as well as research applications. Since diffusion-MRI is a truly quantitative imaging technique, the indices it provides can serve as potential imaging biomarkers which could allow early detection of pathological alterations as well as tracking and possibly predicting subtle changes in follow-up examinations and clinical trials. Accordingly, diffusion-MRI has proven useful in obtaining information to better understand the microstructural changes and neurophysiological mechanisms underlying various neurodegenerative disorders. In this review article, we summarize and explore the main applications, findings, perspectives as well as challenges and future research of diffusion-MRI in various neurodegenerative disorders including Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, Huntington's disease and degenerative ataxias.

Neuroimaging as a New Diagnostic Modality in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is characterized by progressive degeneration of upper and lower motor neurons, with variable involvement of extramotor brain regions. Currently, there are no established objective markers of upper motor neuron and extramotor involvement in ALS. Here, we review the potential diagnostic value of advanced neuroimaging techniques that are increasingly being used to study the brain in ALS. First, we discuss the role of different imaging modalities in our increasing understanding of ALS pathogenesis, and their potential to contribute to objective upper motor neuron biomarkers for the disease. Second, we discuss the challenges to be overcome and the required phases of diagnostic test development to translate imaging technology to clinical care. We also present examples of multidimensional imaging approaches to achieve high levels of diagnostic accuracy. Last, we address the role of neuroimaging in clinical therapeutic trials. Advanced neuroimaging techniques will continue to develop and offer significant opportunities to facilitate the development of new effective treatments for ALS.

Application of high-definition fiber tractography in the management of supratentorial cavernous malformations: a combined qualitative and quantitative approach

BACKGROUND

High-definition fiber tractography (HDFT), an advanced white matter (WM) imaging technique, was evaluated in the management of supratentorial cavernous malformations.

OBJECTIVE

To investigate the relationship of cavernous malformations to the relevant perilesional WM tracts with HDFT and to characterize associated changes first qualitatively and then quantitatively with our novel imaging measure, quantitative anisotropy (QA).

METHODS

Imaging analysis was carried out by researchers blinded to the clinical details. Contralateral WM tracts were used for comparison. Mean QA values were obtained for whole WM tracts. Qualitatively affected superior longitudinal fasciculus/arcuate fibers and corticospinal tracts were further analyzed with the use of mean QA values for the perilesional segments.

RESULTS

Of 10 patients, HDFT assisted with the decision-making process and the offer of surgical resection in 2 patients, lesion approach and removal in 7 patients, and conservative management in 1 patient. Of 17 analyzed WM tracts, HDFT demonstrated partial disruption in 2 tracts, complete disruption in 2 tracts, a combination of displacement and partial disruption in 1 tract, displacement only in 7 tracts, and no change in 5 tracts. Qualitative changes correlated with clinical symptoms. Mean QA values for the whole WM tracts were similar, with the exception of 1 case demonstrating complete disruption of 2 WM tracts. QA-based perilesional segment analysis was consistent with qualitative data in 5 assessed WM tracts.

CONCLUSION

HDFT illustrated the precise spatial relationship of cavernous malformations to multiple WM tracts in a 3-dimensional fashion, optimizing surgical planning, and demonstrated associated disruption and/or displacement, with both occurring perilesionally. These changes were supported by our quantitative marker, which needs further validation.

Prose memory impairment in amyotrophic lateral sclerosis patients is related to hippocampus volume

BACKGROUND AND PURPOSE

Thirty per cent of amyotrophic lateral sclerosis (ALS) patients have non-motor symptoms, including executive and memory deficits. The in vivo anatomical basis of memory deficits in ALS has not been elucidated. In this observational study, brain atrophy in relation to memory function was investigated in ALS patients and controls.

METHODS

Twenty-six ALS patients without dementia and 21 healthy volunteers matched for gender, age and education level underwent comprehensive neuropsychological evaluation and T1- and T2-weighted 3 T magnetic resonance imaging scanning of the brain. Grey and white matter brain volumes were analysed using voxel-based morphometry and age related white matter changes were assessed. The most frequently abnormal memory test (<2 SD below normative data corrected for age, gender and education) was correlated with regional brain volume variations by multiple regression analyses with age, gender and total grey matter volumes as covariates.

RESULTS

Immediate and delayed story recall scores were abnormal in 23% of ALS patients and correlated to bilateral hippocampus grey matter volume (r = 0.52 for both memory tests; P < 0.05; corrected for age, gender and total grey matter volume). This correlation was not found in healthy controls with similar age, education, anxiety and depression levels and white matter changes.

CONCLUSIONS

Prose memory impairment is a frequent finding in this cohort and is associated with hippocampus volume in ALS patients without dementia. These findings complement previous hippocampus changes in imaging studies in ALS and suggest involvement of the hippocampus in cognitive dysfunction of ALS.

The El Escorial criteria: strengths and weaknesses

The El Escorial criteria for the diagnosis of amyotrophic lateral sclerosis (ALS) were established 20 years ago and have been used as inclusion criteria for clinical trials. However, concerns have been raised concerning their use as diagnostic criteria in clinical practice. Moreover, as modern genetics have shed new light on the heterogeneity of ALS and the close relationship between ALS and frontotemporal dementia (FTD) recognized, the World Federation of Neurology Research Group on ALS/MND has initiated discussions to amend and update the criteria, while preserving the essential components for clinical trial enrolment purposes.

Neuroimaging in amyotrophic lateral sclerosis: insights into structural and functional changes

In the past two decades, structural and functional neuroimaging findings have greatly modified longstanding notions regarding the pathophysiology of amyotrophic lateral sclerosis (ALS). Neuroimaging studies have shown that anatomical and functional lesions spread beyond precentral cortices and corticospinal tracts, to include the corpus callosum; frontal, sensory, and premotor cortices; thalamus; and midbrain. Both MRI and PET studies have shown early and diffuse loss of inhibitory cortical interneurons in the motor cortex (increased levels of functional connectivity and loss of GABAergic neurons, respectively) and diffuse gliosis in white-matter tracts. In ALS endophenotypes, neuroimaging has also shown a diverse spreading of lesions and a dissimilar impairment of functional and structural connections. A possible role of PET in the diagnosis of ALS has recently been proposed. However, most neuroimaging studies have pitfalls, such as a small number and poor clinical characterisation of patients, absence of adequate controls, and scarcity of longitudinal assessments. Studies involving international collaborations, standardised assessments, and large patient cohorts will overcome these shortcomings and provide further insight into the pathogenesis of ALS.

Quantifying disease progression in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) exhibits characteristic variability of onset and rate of disease progression, with inherent clinical heterogeneity making disease quantitation difficult. Recent advances in understanding pathogenic mechanisms linked to the development of ALS impose an increasing need to develop strategies to predict and more objectively measure disease progression. This review explores phenotypic and genetic determinants of disease progression in ALS, and examines established and evolving biomarkers that may contribute to robust measurement in longitudinal clinical studies. With targeted neuroprotective strategies on the horizon, developing efficiencies in clinical trial design may facilitate timely entry of novel treatments into the clinic.

The phenotypic variability of amyotrophic lateral sclerosis

Classic textbook neurology teaches that amyotrophic lateral sclerosis (ALS) is a degenerative disease that selectively affects upper and lower motor neurons and is fatal 3-5 years after onset--a description which suggests that the clinical presentation of ALS is very homogenous. However, clinical and postmortem observations, as well as genetic studies, demonstrate that there is considerable variability in the phenotypic expression of ALS. Here, we review the phenotypic variability of ALS and how it is reflected in familial and sporadic ALS, in the degree of upper and lower motor neuron involvement, in motor and extramotor involvement, and in the spectrum of ALS and frontotemporal dementia. Furthermore, we discuss some unusual clinical characteristics regarding presentation, age at onset and disease progression. Finally, we address the importance of this variability for understanding the pathogenesis of ALS and for the development of therapeutic strategies.

Diffusion tensor MRI of chemotherapy-induced cognitive impairment in non-CNS cancer patients: a review

Patients with non-central nervous system cancers often experience subtle cognitive deficits after treatment with cytotoxic agents. Therapy-induced structural changes to the brain could be one of the possible causes underlying these reported cognitive deficits. In this review, we evaluate the use of diffusion tensor imaging (DTI) for assessing possible therapy-induced changes in the microstructure of the cerebral white matter (WM) and provide a critical overview of the published DTI research on therapy-induced cognitive impairment. Both cross-sectional and longitudinal DTI studies have demonstrated abnormal microstructural properties in WM regions involved in cognition. These findings correlated with cognitive performance, suggesting that there is a link between reduced "WM integrity" and chemotherapy-induced impaired cognition. In this paper, we will also introduce the basics of diffusion tensor imaging and how it can be applied to evaluate effects of therapy on structural changes in cerebral WM. The review concludes with considerations and discussion regarding DTI data interpretation and possible future directions for investigating therapy-induced WM changes in cancer patients. This review article is part of a Special Issue entitled: Neuroimaging Studies of Cancer and Cancer Treatment.

Advanced diffusion MRI fiber tracking in neurosurgical and neurodegenerative disorders and neuroanatomical studies: A review

Diffusion MRI enabled in vivo microstructural imaging of the fiber tracts in the brain resulting in its application in a wide range of settings, including in neurological and neurosurgical disorders. Conventional approaches such as diffusion tensor imaging (DTI) have been shown to have limited applications due to the crossing fiber problem and the susceptibility of their quantitative indices to partial volume effects. To overcome these limitations, the recent focus has shifted to the advanced acquisition methods and their related analytical approaches. Advanced white matter imaging techniques provide superior qualitative data in terms of demonstration of multiple crossing fibers in their spatial orientation in a three dimensional manner in the brain. In this review paper, we discuss the advancements in diffusion MRI and introduce their roles. Using examples, we demonstrate the role of advanced diffusion MRI-based fiber tracking in neuroanatomical studies. Results from its preliminary application in the evaluation of intracranial space occupying lesions, including with respect to future directions for prognostication, are also presented. Building upon the previous DTI studies assessing white matter disease in Huntington's disease and Amyotrophic lateral sclerosis; we also discuss approaches which have led to encouraging preliminary results towards developing an imaging biomarker for these conditions.

Central white matter degeneration in bulbar- and limb-onset amyotrophic lateral sclerosis

Previous studies using diffusion tensor imaging (DTI) have examined for differences between bulbar- and limb-onset amyotrophic lateral sclerosis (ALS). Findings between studies have been markedly inconsistent, though possibly as a consequence of poor matching for confounding variables. To address this problem, this study contrasted the DTI profiles of limb-onset (ALS-L) and bulbar-onset (ALS-B) in groups that were tightly matched for the potential confounding effects of power, age, cognitive impairment and motor dysfunction. 14 ALS-L and 14 ALS-B patients were selected from a large prospective study so as to be matched on clinical and demographic features. All subjects, including 29 controls, underwent neuropsychological and neurological assessment. Tract-based spatial statistics and region of interest techniques were used to analyse fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (RD) and axial diffusivity (λ₁). Extensive bilateral FA and RD changes along the corticospinal tract were found in ALS-B compared to controls, p (corrected) <0.05; a similar distribution was seen for ALS-L at a less stringent statistical threshold. ROI analyses also showed more significant changes in ALS-B than ALS-L when each was compared to controls; for FA, MD and RD the changes reached statistical significance in the direct contrast between the two patient groups. With careful matching for confounding factors, the results suggest that ALS-B is associated with greater central white matter degeneration than ALS-L, possibly contributing to the known worse prognosis of ALS-B. The study, however, found no evidence that the spatial distribution of white matter degeneration differs between these groups.

Diffusion tensor tractography analysis of the corpus callosum fibers in amyotrophic lateral sclerosis

BACKGROUND AND PURPOSE

Involvement of the corpus callosum (CC) is reported to be a consistent feature of amyotrophic lateral sclerosis (ALS). We examined the CC pathology using diffusion tensor tractography analysis to identify precisely which fiber bundles are involved in ALS.

METHODS

Diffusion tensor imaging was performed in 14 sporadic ALS patients and 16 age-matched healthy controls. Whole brain tractography was performed using the multiple-region of interest (ROI) approach, and CC fiber bundles were extracted in two ways based on functional and structural relevance: (i) cortical ROI selection based on Brodmann areas (BAs), and (ii) the sulcal-gyral pattern of cortical gray matter using FreeSurfer software, respectively.

RESULTS

The mean fractional anisotropy (FA) values of the CC fibers interconnecting the primary motor (BA4), supplementary motor (BA6), and dorsolateral prefrontal cortex (BA9/46) were significantly lower in ALS patients than in controls, whereas those of the primary sensory cortex (BA1, BA2, BA3), Broca's area (BA44/45), and the orbitofrontal cortex (BA11/47) did not differ significantly between the two groups. The FreeSurfer ROI approach revealed a very similar pattern of abnormalities. In addition, a significant correlation was found between the mean FA value of the CC fibers interconnecting the primary motor area and disease severity, as assessed using the revised Amyotrophic Lateral Sclerosis Functional Rating Scale, and the clinical extent of upper motor neuron signs.

CONCLUSIONS

Our findings suggest that there is some degree of selectivity or a gradient in the CC pathology in ALS. The CC fibers interconnecting the primary motor and dorsolateral prefrontal cortices may be preferentially involved in ALS.

Widespread grey matter pathology dominates the longitudinal cerebral MRI and clinical landscape of amyotrophic lateral sclerosis

Menke/Koerner et al. use structural MRI to explore the extent of longitudinal changes in cerebral pathology in amyotrophic lateral sclerosis, and their relationship to clinical features. A characteristic white matter tract pathological signature is seen cross-sectionally, while cortical involvement dominates longitudinally. This has implications for the development of biomarkers for diagnosis versus therapeutic monitoring.

Diagnosis, stratification and monitoring of disease progression in amyotrophic lateral sclerosis currently rely on clinical history and examination. The phenotypic heterogeneity of amyotrophic lateral sclerosis, including extramotor cognitive impairments is now well recognized. Candidate biomarkers have shown variable sensitivity and specificity, and studies have been mainly undertaken only cross-sectionally. Sixty patients with sporadic amyotrophic lateral sclerosis (without a family history of amyotrophic lateral sclerosis or dementia) underwent baseline multimodal magnetic resonance imaging at 3 T. Grey matter pathology was identified through analysis of T₁-weighted images using voxel-based morphometry. White matter pathology was assessed using tract-based spatial statistics analysis of indices derived from diffusion tensor imaging. Cross-sectional analyses included group comparison with a group of healthy controls (n = 36) and correlations with clinical features, including regional disability, clinical upper motor neuron signs and cognitive impairment. Patients were offered 6-monthly follow-up MRI, and the last available scan was used for a separate longitudinal analysis (n = 27). In cross-sectional study, the core signature of white matter pathology was confirmed within the corticospinal tract and callosal body, and linked strongly to clinical upper motor neuron burden, but also to limb disability subscore and progression rate. Localized grey matter abnormalities were detected in a topographically appropriate region of the left motor cortex in relation to bulbar disability, and in Broca’s area and its homologue in relation to verbal fluency. Longitudinal analysis revealed progressive and widespread changes in the grey matter, notably including the basal ganglia. In contrast there was limited white matter pathology progression, in keeping with a previously unrecognized limited change in individual clinical upper motor neuron scores, despite advancing disability. Although a consistent core white matter pathology was found cross-sectionally, grey matter pathology was dominant longitudinally, and included progression in clinically silent areas such as the basal ganglia, believed to reflect their wider cortical connectivity. Such changes were significant across a range of apparently sporadic patients rather than being a genotype-specific effect. It is also suggested that the upper motor neuron lesion in amyotrophic lateral sclerosis may be relatively constant during the established symptomatic period. These findings have implications for the development of effective diagnostic versus therapeutic monitoring magnetic resonance imaging biomarkers. Amyotrophic lateral sclerosis may be characterized initially by a predominantly white matter tract pathological signature, evolving as a widespread cortical network degeneration.

Use of diffusion spectrum imaging in preliminary longitudinal evaluation of amyotrophic lateral sclerosis: development of an imaging biomarker

Previous diffusion tensor imaging (DTI) studies have shown white matter pathology in amyotrophic lateral sclerosis (ALS), predominantly in the motor pathways. Further these studies have shown that DTI can be used longitudinally to track pathology over time, making white matter pathology a candidate as an outcome measure in future trials. DTI has demonstrated application in group studies, however its derived indices, for example fractional anisotropy, are susceptible to partial volume effects, making its role questionable in examining individual progression. We hypothesize that changes in the white matter are present in ALS beyond the motor tracts, and that the affected pathways and associated pattern of disease progression can be tracked longitudinally using automated diffusion connectometry analysis. Connectometry analysis is based on diffusion spectrum imaging and overcomes the limitations of a conventional tractography approach and DTI. The identified affected white matter tracts can then be assessed in a targeted fashion using High definition fiber tractography (a novel white matter MR imaging technique). Changes in quantitative and qualitative markers over time could then be correlated with clinical progression. We illustrate these principles toward developing an imaging biomarker for demonstrating individual progression, by presenting results for five ALS patients, including with longitudinal data in two. Preliminary analysis demonstrated a number of changes bilaterally and asymmetrically in motoric and extramotoric white matter pathways. Further the limbic system was also affected possibly explaining the cognitive symptoms in ALS. In the two longitudinal subjects, the white matter changes were less extensive at baseline, although there was evidence of disease progression in a frontal pattern with a relatively spared postcentral gyrus, consistent with the known pathology in ALS.

Lessons of ALS imaging: Pitfalls and future directions - A critical review

Background

While neuroimaging in ALS has gained unprecedented momentum in recent years, little progress has been made in the development of viable diagnostic, prognostic and monitoring markers.

Objectives

To identify and discuss the common pitfalls in ALS imaging studies and to reflect on optimal study designs based on pioneering studies.

Methods

A “PubMed”-based literature search on ALS was performed based on neuroimaging-related keywords. Study limitations were systematically reviewed and classified so that stereotypical trends could be identified.

Results

Common shortcomings, such as relatively small sample sizes, statistically underpowered study designs, lack of disease controls, poorly characterised patient cohorts and a large number of conflicting studies, remain a significant challenge to the field. Imaging data of ALS continue to be interpreted at a group-level, as opposed to meaningful individual-patient inferences.

Conclusions

A systematic, critical review of ALS imaging has identified stereotypical shortcomings, the lessons of which should be considered in the design of future prospective MRI studies. At a time when large multicentre studies are underway a candid discussion of these factors is particularly timely.

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Stereotypical shortcomings can be identified in ALS neuroimaging studies.

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A systematic discussion of ALS study limitations is particularly timely.

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Individual patient data meta-analyses and multicentre studies are urgently required.

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The gaps identified in ALS imaging indicate exciting research opportunities.

Deciphering amyotrophic lateral sclerosis: what phenotype, neuropathology and genetics are telling us about pathogenesis

Amyotrophic lateral sclerosis (ALS) is characterized phenotypically by progressive weakness and neuropathologically by loss of motor neurons. Phenotypically, there is marked heterogeneity. Typical ALS has mixed upper motor neuron (UMN) and lower motor neuron (LMN) involvement. Primary lateral sclerosis has predominant UMN involvement. Progressive muscular atrophy has predominant LMN involvement. Bulbar and limb ALS have predominant regional involvement. Frontotemporal dementia has significant cognitive and behavioral involvement. These phenotypes can be so distinctive that they would seem to have differing biology. However, they cannot be distinguished, at least neuropathologically or genetically. In sporadic ALS (SALS), they are mostly characterized by ubiquitinated cytoplasmic inclusions of TDP-43. In familial ALS (FALS), where phenotypes are indistinguishable from SALS and similarly heterogeneous, each mutated gene has its own genetic and molecular signature. Overall, since the same phenotypes can have multiple causes including different gene mutations, there must be multiple molecular mechanisms causing ALS - and ALS is a syndrome. Since, however, multiple phenotypes can be caused by one single gene mutation, a single molecular mechanism can cause heterogeneity. What the mechanisms are remain unknown, but active propagation of the pathology neuroanatomically seems to be a principal component. Leading candidate mechanisms include RNA processing, cell-cell interactions between neurons and non-neuronal neighbors, focal seeding from a misfolded protein that has prion-like propagation, and fatal errors introduced during neurodevelopment of the motor system. If fundamental mechanisms could be identified and understood, ALS therapy could rationally target progression and stop the disease - a goal that seems increasingly achievable.

Mechanisms, models and biomarkers in amyotrophic lateral sclerosis

The last 30 years have seen a major advance in the understanding of the clinical and pathological heterogeneity of amyotrophic lateral sclerosis (ALS), and its overlap with frontotemporal dementia. Multiple, seemingly disparate biochemical pathways converge on a common clinical syndrome characterized by progressive loss of upper and lower motor neurons. Pathogenic themes in ALS include excitotoxicity, oxidative stress, mitochondrial dysfunction, neuroinflammation, altered energy metabolism, and most recently RNA mis-processing. The transgenic rodent, overexpressing mutant superoxide dismutase-1, is now only one of several models of ALS pathogenesis. The nematode, fruit fly and zebrafish all offer fresh insight, and the development of induced pluripotent stem cell-derived motor neurons holds promise for the screening of candidate therapeutics. The lack of useful biomarkers in ALS contributes to diagnostic delay, and the inability to stratify patients by prognosis may be an important factor in the failure of therapeutic trials. Biomarkers sensitive to disease activity might lessen reliance on clinical measures and survival as trial endpoints and reduce study length. Emerging proteomic markers of neuronal loss and glial activity in cerebrospinal fluid, a cortical signature derived from advanced structural and functional MRI, and the development of more sensitive measurements of lower motor neuron physiology are leading a new phase of biomarker-driven therapeutic discovery.

Multimodal tract-based analysis in ALS patients at 7T: a specific white matter profile?

Our objective was to explore the value of additional MR contrasts in elucidating the decrease in fractional anisotropy (FA) as has been observed in the corticospinal tracts (CST) of patients with amyotrophic lateral sclerosis (ALS). Eleven patients and nine healthy control subjects were scanned at 3T and 7T MRI. Whole brain and tract specific comparison was performed of both diffusion weighted (3T), quantitative T1 (qT1), magnetization transfer ratio (MTR) and amide proton transfer weighted (APTw) imaging (7T). Results of whole brain comparison using histogram analyses showed no significant differences between patients and controls. Measures along the CST showed a significantly reduced FA together with a significantly increased diffusivity perpendicular to the tract direction in patients compared to controls. In addition, patients showed a small but significant increase in MTR values within the right CST. No significant changes were observed in qT1 and APTw values. In conclusion, our findings, based on a multimodal approach, revealed that the decrease in FA is most probably caused by an increased diffusivity perpendicular to the CST. This diffusivity profile, together with the increase in MTR is inconsistent with demyelination but consistent with an increase of free liquid spins in the white matter tissue.

Extramotor damage is associated with cognition in primary lateral sclerosis patients

Objectives

This is a cross-sectional study aimed at investigating cognitive performances in patients with primary lateral sclerosis (PLS) and using diffusion tensor (DT) magnetic resonance imaging (MRI) to determine the topographical distribution of microstructural white matter (WM) damage in patients with or without cognitive deficits.

Methods

DT MRI scans were obtained from 21 PLS patients and 35 age- and sex-matched healthy controls. All PLS patients underwent a comprehensive neuropsychological battery. Tract-based-spatial-statistics (TBSS) was used to perform a whole-brain voxel-wise analysis of fractional anisotropy (FA), axial, radial (radD) and mean diffusivity (MD).

Results

Ten PLS patients had abnormal scores in at least one neuropsychological test (PLS with cognitive deficits, PLS-cd). Compared with healthy controls and cognitively unimpaired PLS patients (PLS-cu), PLS-cd cases showed decreased FA and increased MD and radD in the corticospinal tract (CST), corpus callosum, brainstem, anterior limb of internal capsule, superior and inferior longitudinal fasciculi, fornix, thalamic radiations, and parietal lobes, bilaterally. Compared with healthy controls, PLS-cd patients showed further decreased FA and increased radD in the cerebellar WM, bilaterally. Compared with controls, PLS-cu patients showed decreased FA in the mid-body of corpus callosum. In PLS, executive and language test scores correlated with WM damage.

Conclusions

This is the first study evaluating the relationship between cognitive performance and WM tract damage in PLS patients. PLS can be associated with a multi-domain cognitive impairment. WM damage to interhemispheric, limbic and major associative WM tracts seem to be the structural correlate of cognitive abnormalities in these patients.

Amyotrophic lateral sclerosis--a model of corticofugal axonal spread

The pathological process underlying amyotrophic lateral sclerosis (ALS) is associated with the formation of cytoplasmic inclusions consisting mainly of phosphorylated 43-kDa transactive response DNA-binding protein (pTDP-43), which plays an essential part in the pathogenesis of ALS. Preliminary evidence indicates that neuronal involvement progresses at different rates, but in a similar sequence, in different patients with ALS. This observation supports the emerging concept of prion-like propagation of abnormal proteins in noninfectious neurodegenerative diseases. Although the distance between involved regions is often considerable, the affected neurons are connected by axonal projections, indicating that physical contacts between nerve cells along axons are important for dissemination of ALS pathology. This article posits that the trajectory of the spreading pattern is consistent with the induction and dissemination of pTDP-43 pathology chiefly from cortical neuronal projections, via axonal transport, through synaptic contacts to the spinal cord and other regions of the brain.

Identification and interpretation of microstructural abnormalities in motor pathways in adolescents born preterm

There has been extensive interest in assessing the long-term effects of preterm birth on brain white matter microstructure using diffusion MRI. Our aim in this study is to explore diffusion MRI differences between adolescents born preterm and term born controls, with a specific interest in characterising how such differences are manifested in white matter regions containing predominantly single or crossing fibre populations. Probabilistic high angular resolution tractography together with large deformation spatial normalisation were used to objectively investigate diffusion tensor parameters at regular intervals along fibre tracts of 45 adolescents born before 33 weeks of gestation and 30 term-born typically developing adolescents. Diffusion parameters were significantly different between preterms and controls at several levels along the cortico-spinal, thalamo-cortical and transcallosal pathways. Within the predominantly single fibre regions of the corpus callosum and internal capsule, in the preterms mean diffusivity (MD) was found to be increased while fractional anisotropy (FA) was decreased compared to controls. In contrast, however, where these pathways traversed the centrum semiovale, FA and MD were both significantly increased. The major contributor to reduced FA in preterms in predominantly single fibre regions was the increased radial eigenvalue (i.e. increased radial diffusivity). In predominantly crossing-fibre regions, the tensor eigenvalues are not meaningful, and the observed increase in FA is likely to be due to a decrease in anisotropy in one of the contributing fibre bundles. Similar differences (although less pronounced) were observed after excluding preterms with radiological signs of preterm brain injury from the sample. In summary, white matter microstructure was found to be altered in motor pathways in adolescents born preterm. Disruption of white matter (WM) microstructure in a single fibre region with resulting higher radial diffusivity leads to lower FA, whereas selective disruption of one fibre population in a crossing fibre region is observed to lead to higher FA. These findings challenge the common simplistic interpretation of FA as a measure of WM tract integrity.

Resting state functional connectivity alterations in primary lateral sclerosis

Resting state functional connectivity of the sensorimotor and extramotor brain networks was studied in 24 patients with primary lateral sclerosis (PLS) relative to 26 healthy controls. The relationships of RS functional connectivity with patient clinical and cognitive status and white matter tract damage (i.e., corticospinal tracts, corpus callosum, and superior longitudinal fasciculus) were investigated. Compared with controls, PLS patients showed an increased functional connectivity within the sensorimotor, frontal, and left frontoparietal networks spanning the pre- and postcentral, medial and dorsal frontal, insular, and superior temporal regions. Patients with more severe physical disability and a more rapid rate of disease progression had increased sensorimotor connectivity values. The increased functional connectivity within the frontal network was associated with executive dysfunction. In addition, higher functional connectivity correlated with greater structural damage to network-specific white matter tracts. This study shows clinically meaningful increased resting state functional connectivity in PLS.

25 years of neuroimaging in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal motor neuron disease for which a precise cause has not yet been identified. Standard CT or MRI evaluation does not demonstrate gross structural nervous system changes in ALS, so conventional neuroimaging techniques have provided little insight into the pathophysiology of this disease. Advanced neuroimaging techniques--such as structural MRI, diffusion tensor imaging and proton magnetic resonance spectroscopy--allow evaluation of alterations of the nervous system in ALS. These alterations include focal loss of grey and white matter and reductions in white matter tract integrity, as well as changes in neural networks and in the chemistry, metabolism and receptor distribution in the brain. Given their potential for investigation of both brain structure and function, advanced neuroimaging methods offer important opportunities to improve diagnosis, guide prognosis, and direct future treatment strategies in ALS. In this article, we review the contributions made by various advanced neuroimaging techniques to our understanding of the impact of ALS on different brain regions, and the potential role of such measures in biomarker development.

Grey matter correlates of clinical variables in amyotrophic lateral sclerosis (ALS): a neuroimaging study of ALS motor phenotype heterogeneity and cortical focality

BACKGROUND

Body region of onset and functional disability are key components of disease heterogeneity in amyotrophic lateral sclerosis (ALS).

OBJECTIVES

To evaluate patterns of grey matter pathology in the motor cortex and correlate focal structural changes with functional disability.

METHODS

We conducted a single-centre neuroimaging study of a cohort of 33 cognitively normal patients with amyotrophic lateral sclerosis (ALS) and 44 healthy controls. A voxel-wise generalised linear model was used to investigate the distribution of disease burden within the motor cortex in relation to clinical disability.

RESULTS

Patients with bulbar onset have bilateral focal atrophy in the bulbar segment of the motor homunculus compared with patients with limb onset who have focal cortical changes in the limb segment of their motor strip. Furthermore, the extent to which different body regions are affected in ALS corresponds to the extent of focal grey matter loss in the primary motor cortex. Cortical ALS pathology also extends beyond the motor cortex affecting frontal, occipital and temporal regions.

CONCLUSIONS

Focal grey matter atrophy within the motor homunculus corresponds with functional disability in ALS. The findings support the existing concepts of cortical focality and motor phenotype heterogeneity in ALS.

A prospective pilot study measuring muscle volumetric change in amyotrophic lateral sclerosis

Our objective was to investigate the potential of muscle volume, measured with magnetic resonance (MR), as a biomarker to quantify disease progression in patients with amyotrophic lateral sclerosis (ALS). In this longitudinal pilot study, we first sought to determine the stability of volumetric muscle MR measurements in 11 control subjects at two time-points. We assessed feasibility of detecting atrophy in four patients with ALS, followed at three-month intervals for 12 months. Muscle power and MR volume were measured in thenar eminence (TEm), first dorsal interosseous (1DIO), tibialis anterior (TA) and tongue. Changes over time were assessed using linear regression models and t-tests. Results demonstrated that, in controls, no volumetric MR changes were seen (mean volume variation in all muscles < 5%, p > 0.1). In patients, between-subject heterogeneity was identified. Trends for volume loss were found in TEm (mean, - 26.84%, p = 0.056) and TA (- 8.29%, p = 0.077), but not in 1DIO (- 18.47%, p = 0.121) or tongue (< 5%, p = 0.367). In conclusion, volumetric muscle MR appears a stable measure in controls, and progressive volume loss was demonstrable in individuals with ALS in whom clinical weakness progressed. In this small study, subclinical atrophy was not demonstrable using muscle MR. Clinico-radiological discordance between muscle weakness and MR atrophy could reflect a contribution of upper motor neuron pathology.