Fatigue in Multiple Sclerosis: A Resting-State EEG Microstate Study

Fatigue affects approximately 80% of people with Multiple Sclerosis (PwMS) and can impact several domains of daily life. However, the neural underpinnings of fatigue in MS are still not completely clear. The aim of our study was to investigate the spontaneous large-scale networks functioning associated with fatigue in PwMS using the EEG microstate approach with a spectral decomposition. Forty-three relapsing-remitting MS patients and twenty-four healthy controls (HCs) were recruited. All participants underwent an administration of Modified Fatigue Impact scale (MFIS) and a 15-min resting-state high-density EEG recording. We compared the microstates of healthy subjects, fatigued (F-MS) and non-fatigued (nF-MS) patients with MS; correlations with clinical and behavioral fatigue scores were also analyzed. Microstates analysis showed six templates across groups and frequencies. We found that in the F-MS emerged a significant decrease of microstate F, associated to the salience network, in the broadband and in the beta band. Moreover, the microstate B, associated to the visual network, showed a significant increase in fatigued patients than healthy subjects in broadband and beta bands. The multiple linear regression showed that the high cognitive fatigue was predicted by both an increase and decrease, respectively, in delta band microstate B and beta band microstate F. On the other hand, higher physical fatigue was predicted with lower occurrence microstate F in beta band. The current findings suggest that in MS the higher level of fatigue might be related to a maladaptive functioning of the salience and visual network.

A cluster-randomised controlled feasibility trial evaluating the Cognitive Occupation-Based programme for people with Multiple Sclerosis (COB-MS)

INTRODUCTION

There is a high prevalence of cognitive difficulties in MS, but despite this, there are few programmes targeting cognition that focus on the ability to function well in everyday life. The Cognitive Occupation-Based programme for people with Multiple Sclerosis (COB-MS), an occupation-focused cognitive intervention, was developed to address this. It addresses both the functional difficulties and the wide-ranging symptoms that present in MS.

OBJECTIVE

Here we report on the results of a cluster-randomised controlled feasibility trial (ISRCTN11462710; registered 4th September 2019) evaluating the COB-MS in terms of feasibility and initial efficacy as a cognitive intervention for people with MS.

METHOD

The eight-session COB-MS intervention was delivered remotely by occupational therapists to participants with MS in the intervention group. Following the end of the trial the COB-MS was delivered to the wait-list control group. Data was collected from people with MS experiencing cognitive difficulties at baseline, post-intervention, 12-weeks, and 6-month follow-up. The primary outcome measure was the Goal Attainment Scaling at 12 weeks. Data was also collected in the domains of cognition, quality of life, and mood.

RESULTS

One hundred and eighteen people with MS and cognitive difficulties were randomised to either usual care (n = 60) or COB-MS intervention (n = 58). Ninety-four participants were retained at 6-month follow-up. The COB-MS was found to be feasible, including trial procedures and protocol. Data indicates that the COB-MS is accepted by participants and had positive impacts on daily life. Those allocated to the COB-MS group had a significant improvement in the primary outcome compared to the control condition. Progression criteria set for the feasibility trial have been met therefore further testing of the COB-MS at a definitive trial is supported by the results.

CONCLUSION

The results provide a strong basis for a pathway to a future definitive trial of COB-MS, with respect to both feasibility and preliminary, clinical efficacy.

TRIAL REGISTRATION

ISRCTN11462710 Date of registration: 4th September 2019.

Monoaminergic network abnormalities are associated with fatigue in pediatric multiple sclerosis

BACKGROUND

Fatigue is commonly observed in pediatric multiple sclerosis (pedMS) patients, but its underlying mechanisms remain largely unexplored. We evaluated whether resting-state (RS) functional connectivity (FC) abnormalities in monoaminergic networks contributed to explain fatigue in pedMS.

METHODS

Fifty-five pedMS and twenty-three matched healthy controls (HC) underwent clinical and RS functional MRI assessment. Patients with Fatigue Severity Scale (FSS) score ≥ 4 were classified as fatigued (F). Patterns of dopamine-, noradrenaline- and serotonin-related RS FC were derived by constrained independent component analysis, using PET atlases for dopamine, noradrenaline, and serotonin transporters obtained in HCs' brain.

RESULTS

Compared to non-fatigued (NF)-pedMS patients and HC, F-pedMS patients (15/55, 27.3%) showed decreased dopamine-related RS FC in the right postcentral gyrus. They also showed decreased dopamine-related RS FC in the left insula vs. HC and increased dopamine-related RS FC in the left middle temporal gyrus and cerebellum (lobule VI) vs. NF patients. In the noradrenaline-related network, F-pedMS patients showed decreased RS FC in the left superior parietal lobule and increased RS FC in the right thalamus vs. HC and NF-pedMS. Compared to HC, F-pedMS patients also showed decreased RS FC in the right calcarine cortex and increased RS FC in the right middle frontal gyrus. In the serotonin-related network, F-pedMS patients showed decreased RS FC in the right angular gyrus and increased RS FC in the right postcentral gyrus vs. NF-pedMS patients.

DISCUSSION

In pedMS, fatigue is associated with specific monoaminergic network abnormalities, providing pathological markers for this bothersome symptom and putative targets for its treatment.

Resting state functional connectivity modifications in monoaminergic circuits underpin fatigue development in patients with multiple sclerosis

Dysregulation of monoaminergic networks might have a role in the pathogenesis of fatigue in multiple sclerosis (MS). We investigated longitudinal changes of resting state (RS) functional connectivity (FC) in monoaminergic networks and their association with the development of fatigue in MS. Eighty-nine MS patients and 49 age- and sex-matched healthy controls (HC) underwent neurological, fatigue, and RS functional MRI assessment at baseline and after a median follow-up of 1.3 years (interquartile range = 1.01-2.01 years). Monoaminergic-related RS FC was estimated with an independent component analysis constrained to PET atlases for dopamine (DA), noradrenaline (NA), and serotonin (5-HT) transporters. At baseline, 24 (27%) MS patients were fatigued (F) and 65 were not fatigued (NF). Of these, 22 (34%) developed fatigue (DEV-FAT) at follow-up and 43 remained not fatigued (NO-FAT). At baseline, F-MS patients showed increased monoaminergic-related RS FC in the caudate nucleus vs NF-MS and in the hippocampal, postcentral, temporal, and occipital cortices vs NF-MS and HC. Moreover, F-MS patients exhibited decreased RS FC in the frontal cortex vs NF-MS and HC, and in the thalamus vs NF-MS. During the follow-up, no RS FC changes were observed in HC. NO-FAT patients showed limited DA-related RS FC modifications, whereas DEV-FAT MS patients showed increased DA-related RS FC in the left hippocampus, significant at time-by-group interaction analysis. In the NA-related network, NO-FAT patients showed decreased RS FC over time in the left superior frontal gyrus. This region showed increased RS FC in both DEV-FAT and F-MS patients; this divergent behavior was significant at time-by-group interaction analysis. Finally, DEV-FAT MS patients presented increased 5-HT-related RS FC in the angular and middle occipital gyri, while this latter region showed decreased 5-HT-related RS FC during the follow-up in F-MS patients. In MS patients, distinct patterns of alterations were observed in monoaminergic networks based on their fatigue status. Fatigue was closely linked to specific changes in the basal ganglia and hippocampal, superior frontal, and middle occipital cortices.

Multisensory mental imagery of fatigue in patients with multiple Sclerosis. Preliminary evidence from a fMRI study

Fatigue, defined as a subjective lack of physical and/or mental energy, is a clinical symptom highly characterizing multiple sclerosis (MS). The present study utilized a novel approach to the study of fatigue, examining first person-mental imagery of the symptom. Eighteen right-handed patients with MS (14F, 4 M, mean age 45.8 ± 8.15 years) were evaluated and were compared to nineteen healthy controls (10F, 9 M, mean age 43.15 ± 8.34 years) Patients were all in relapsing remitting form and no patient had presented relapses in the 6 months prior to inclusion in the study. We evaluated their behavioral performance and fMRI activations. We used an fMRI paradigm used to trigger first person-mental imagery of fatigue, through short sentences describing the principal manifestations of fatigue. Participants were asked to imagine the corresponding sensations (Sensory Imagery, SI). As a control, they had to imagine the visual scenes (Visual Imagery, VI) described in short phrases. They made a vividness rating by pressing the corresponding button. Behaviorally, we found that patients' mean scores at the Multidimensional Fatigue Symptom Inventory for the general scale, physical scale, and mental scale were significantly higher than healthy controls (p = 0.05, p = 0.002, p = 0.006 respectively), but not for the emotional scale and for vigor scale (p = 0.207, n.s., p = 0.06, n.s.). In the imagery fMRI task, patients were significantly slower (mean reaction times and standard deviation: 2.24 s ± 0.33) than controls (mean reaction times and standard deviation: 1.918 s ± 0.455) for the SI task (Z=-2.058, p = 0.040), while no significant difference was found for the VI task. Regarding brain mapping, our main result is a group by task interaction. The SI task (vs. VI task) in healthy controls (relative to patients) increased activation in the left inferior parietal lobule. These preliminary results indicate that fatigue is related to dysfunctions in higher-order aspects of motor control, given the role of the posterior parietal lobe in motor planning and multisensory integration.

Disrupted hemodynamic response within dorsolateral prefrontal cortex during cognitive tasks among people with multiple sclerosis-related fatigue

INTRODUCTION

Mental fatigue is an early and enduring symptom in persons with autoimmune disease particularly multiple sclerosis (MS). Neuromodulation has emerged as a potential treatment although optimal cortical targets have yet to be determined. We aimed to examine cortical hemodynamic responses within bilateral dorsolateral prefrontal cortex (dlPFC) and frontopolar areas during single and dual cognitive tasks in persons with MS-related fatigue compared to matched controls.

METHODS

We recruited persons (15 MS and 12 age- and sex-matched controls) who did not have physical or cognitive impairment and were free from depressive symptoms. Functional near infrared spectroscopy (fNIRS) registered hemodynamic responses during the tasks. We calculated oxyhemoglobin peak, time-to-peak, coherence between channels (a potential marker of neurovascular coupling) and functional connectivity (z-score).

RESULTS

In MS, dlPFC demonstrated disrupted hemodynamic coherence during both single and dual tasks, as evidenced by non-significant and negative correlations between fNIRS channels. In MS, reduced coherence occurred in left dorsolateral PFC during the single task but occurred bilaterally as the task became more challenging. Functional connectivity was lower during dual compared to single tasks in the right dorsolateral PFC in both groups. Lower z-score was related to greater feelings of fatigue. Peak and time-to-peak hemodynamic response did not differ between groups or tasks.

CONCLUSIONS

Hemodynamic responses were inconsistent and disrupted in people with MS experiencing mental fatigue, which worsened as the task became more challenging. Our findings point to dlPFC, but not frontopolar areas, as a potential target for neuromodulation to treat cognitive fatigue.

Brain stimulation for patients with multiple sclerosis: an umbrella review of therapeutic efficacy

Multiple sclerosis patients often experience various symptoms that can greatly impact their quality of life. There are various brain stimulation techniques that have been evaluated for their ability to reduce the symptoms of multiple sclerosis. However, there is inconsistency in the specific stimulation methods used and the symptoms targeted in the existing research. This umbrella review conducted in order to evaluate the effectiveness of brain stimulation and identify limitations and gaps for further research. In this umbrella review, we conducted a searched on Web of Knowledge, PubMed, and Scopus database. We specifically looked for reviews, with or without meta-analyses, that have investigated the effects of brain stimulation methods on symptoms of multiple sclerosis. All articles were examined by AMSTAR 2 (A Measure Tool to Assess Systematic Review 2). We identified 155 articles, of which 14 were eligible for inclusion. Of those, five were qualitative studies and nine were meta-analyses. Among the included studies, four examined the use of deep brain stimulation, while ten investigated the therapeutic potential of noninvasive brain stimulation. Considering the heterogeneity of studies, the current evidence suggests that repetitive transcranial magnetic stimulation may be effective in treating pain and improving motor function, while transcranial direct current stimulation may be useful in alleviating fatigue and enhancing certain aspects of cognitive performance. Deep brain stimulation, on the other hand, appears to be effective in reducing tremors. However, further research is warranted to validate these findings and address the existing limitations in the field.

Functional gradients reveal cortical hierarchy changes in multiple sclerosis

Functional gradient (FG) analysis represents an increasingly popular methodological perspective for investigating brain hierarchical organization but whether and how network hierarchy changes concomitant with functional connectivity alterations in multiple sclerosis (MS) has remained elusive. Here, we analyzed FG components to uncover possible alterations in cortical hierarchy using resting-state functional MRI (rs-fMRI) data acquired in 122 MS patients and 97 healthy control (HC) subjects. Cortical hierarchy was assessed by deriving regional FG scores from rs-fMRI connectivity matrices using a functional parcellation of the cerebral cortex. The FG analysis identified a primary (visual-to-sensorimotor) and a secondary (sensory-to-transmodal) component. Results showed a significant alteration in cortical hierarchy as indexed by regional changes in FG scores in MS patients within the sensorimotor network and a compression (i.e., a reduced standard deviation across all cortical parcels) of the sensory-transmodal gradient axis, suggesting disrupted segregation between sensory and cognitive processing. Moreover, FG scores within limbic and default mode networks were significantly correlated (ρ = 0.30 $$ \rho =0.30 $$ , p < .005 after Bonferroni correction for both) with the symbol digit modality test (SDMT) score, a measure of information processing speed commonly used in MS neuropsychological assessments. Finally, leveraging supervised machine learning, we tested the predictive value of network-level FG features, highlighting the prominent role of the FG scores within the default mode network in the accurate prediction of SDMT scores in MS patients (average mean absolute error of 1.22 ± 0.07 points on a hold-out set of 24 patients). Our work provides a comprehensive evaluation of FG alterations in MS, shedding light on the hierarchical organization of the MS brain and suggesting that FG connectivity analysis can be regarded as a valuable approach in rs-fMRI studies across different MS populations.

Altered functional connectivity in patients with post-stroke fatigue: A resting-state fMRI study

BACKGROUND

Post-stroke fatigue (PSF) was a common complication after stroke. This study aimed to explore the neuroimaging mechanism of PSF, which was rarely studied.

METHODS

Patients with the first episode of ischemic stroke were recruited from the First Affiliated Hospital of Wenzhou Medical University between March 2021 and December 2022. The fatigue severity scale (FSS) was used to assess fatigue symptoms. PSF was diagnosed by a neurologist based on the FSS score and PSF diagnostic criteria. All the patients were scanned by resting-state functional MRI (rs-fMRI). Precuneus, the posterior node of default-mode network (pDMN), was related to fatigue. Therefore, imaging data were further analyzed by the seed-based resting-state functional connectivity (FC) approach, with the left (PCUN.L) and right precuneus (PCUN.R) being the seeds.

RESULTS

A total of 70 patients with acute ischemic stroke were finally recruited, comprising 40 patients with PSF and 30 patients without PSF. Both the PCUN.L and PCUN.R seeds (pDMN) exhibited decreased FC with the prefrontal lobes located at the anterior part of DMN (aDMN), and the FC values were negatively correlated with FSS scores (both p < 0.001). These two seeds also exhibited increased FC with the right insula, and the FC values were positively correlated with FSS scores (both p < 0.05).

CONCLUSION

The abnormal FC between the aDMN and pDMN was associated with PSF. Besides, the insula, related to interoception, might also play an important role in PSF.

Hub overload and failure as a final common pathway in neurological brain network disorders

Understanding the concept of network hubs and their role in brain disease is now rapidly becoming important for clinical neurology. Hub nodes in brain networks are areas highly connected to the rest of the brain, which handle a large part of all the network traffic. They also show high levels of neural activity and metabolism, which makes them vulnerable to many different types of pathology. The present review examines recent evidence for the prevalence and nature of hub involvement in a variety of neurological disorders, emphasizing common themes across different types of pathology. In focal epilepsy, pathological hubs may play a role in spreading of seizure activity, and removal of such hub nodes is associated with improved outcome. In stroke, damage to hubs is associated with impaired cognitive recovery. Breakdown of optimal brain network organization in multiple sclerosis is accompanied by cognitive dysfunction. In Alzheimer's disease, hyperactive hub nodes are directly associated with amyloid-beta and tau pathology. Early and reliable detection of hub pathology and disturbed connectivity in Alzheimer's disease with imaging and neurophysiological techniques opens up opportunities to detect patients with a network hyperexcitability profile, who could benefit from treatment with anti-epileptic drugs.

Brain connectivity changes underlying depression and fatigue in relapsing-remitting multiple sclerosis: A systematic review

Multiple Sclerosis (MS) is an autoimmune disease affecting the central nervous system, characterised by neuroinflammation and neurodegeneration. Fatigue and depression are common, debilitating, and intertwined symptoms in people with relapsing-remitting MS (pwRRMS). An increased understanding of brain changes and mechanisms underlying fatigue and depression in RRMS could lead to more effective interventions and enhancement of quality of life. To elucidate the relationship between depression and fatigue and brain connectivity in pwRRMS we conducted a systematic review. Searched databases were PubMed, Web-of-Science and Scopus. Inclusion criteria were: studied participants with RRMS (n ≥ 20; ≥ 18 years old) and differentiated between MS subtypes; published between 2001-01-01 and 2023-01-18; used fatigue and depression assessments validated for MS; included brain structural, functional magnetic resonance imaging (fMRI) or diffusion MRI (dMRI). Sixty studies met the criteria: 18 dMRI (15 fatigue, 5 depression) and 22 fMRI (20 fatigue, 5 depression) studies. The literature was heterogeneous; half of studies reported no correlation between brain connectivity measures and fatigue or depression. Positive findings showed that abnormal cortico-limbic structural and functional connectivity was associated with depression. Fatigue was linked to connectivity measures in cortico-thalamic-basal-ganglial networks. Additionally, both depression and fatigue were related to altered cingulum structural connectivity, and functional connectivity involving thalamus, cerebellum, frontal lobe, ventral tegmental area, striatum, default mode and attention networks, and supramarginal, precentral, and postcentral gyri. Qualitative analysis suggests structural and functional connectivity changes, possibly due to axonal and/or myelin loss, in the cortico-thalamic-basal-ganglial and cortico-limbic network may underlie fatigue and depression in pwRRMS, respectively, but the overall results were inconclusive, possibly explained by heterogeneity and limited number of studies. This highlights the need for further studies including advanced MRI to detect more subtle brain changes in association with depression and fatigue. Future studies using optimised imaging protocols and validated depression and fatigue measures are required to clarify the substrates underlying these symptoms in pwRRMS.

Investigating the link between regional oxygen metabolism and cognitive speed in multiple sclerosis: Implications for fatigue

BACKGROUND

Most multiple sclerosis (MS) patients experience fatigue and cognitive decline but the underlying mechanisms remain unknown. Previous work has shown whole brain resting cerebral metabolic rate of oxygen (CMRO2) is associated with the extent of these symptoms. However, it is not known if the association between global CMRO2 and MS-related cognitive speed and fatigue can be localized to specific brain regions. Based upon previous research suggesting prefrontal involvement in MS-related changes in cognitive speed and fatigue, we hypothesized that oxygen metabolic changes within prefrontal cortex (PFC) might form the pathophysiologic basis of cognitive performance and fatigue in MS patients.

OBJECTIVE

Investigate whether PFC ΔCMRO2 is associated with cognitive speed and fatigue in MS.

METHODS

MS and healthy control (HC) participants were scanned using a dual--echo fMRI sequence and underwent a hypercapnia calibration experiment that permitted estimation of ΔCMRO2 while performing a scanner version of symbol-digit modalities task, a measure of information processing speed and utilized in the clinic as a reliable sentinel biomarker for global cognitive impairment in MS. Participants then completed the Modified Fatigue Impact Scale (MFIS) to measure fatigue.

RESULTS

MS patients exhibited significant reductions in cognitive performance relative to HCs (p < 0.04). Prefrontal ΔCMRO2 explained significant variability (ΔR2 = 0.11) in cognitive speed, over and above disease and demographic variables, for the MS group only. Prefrontal ΔCMRO2 was not associated with fatigue across groups. ΔCMRO2 in visual and motor areas were not associated with cognitive performance or fatigue for either group.

CONCLUSION

Prefrontal oxygen metabolism may be a sensitive measure of MS-related cognitive decline.

Altered neural intrinsic oscillations in patients with multiple sclerosis: effects of cortical thickness

Objective

To investigate the effects of cortical thickness on the identification accuracy of fractional amplitude of low-frequency fluctuation (fALFF) in patients with multiple sclerosis (MS).

Methods

Resting-state functional magnetic resonance imaging data were collected from 31 remitting MS, 20 acute MS, and 42 healthy controls (HCs). After preprocessing, we first calculated two-dimensional fALFF (2d-fALFF) maps using the DPABISurf toolkit, and 2d-fALFF per unit thickness was obtained by dividing 2d-fALFF by cortical thickness. Then, between-group comparison, clinical correlation, and classification analyses were performed in 2d-fALFF and 2d-fALFF per unit thickness maps. Finally, we also examined whether the effect of cortical thickness on 2d-fALFF maps was affected by the subfrequency band.

Results

In contrast with 2d-fALFF, more changed regions in 2d-fALFF per unit thickness maps were detected in MS patients, such as increased region of the right inferior frontal cortex and faded regions of the right paracentral lobule, middle cingulate cortex, and right medial temporal cortex. There was a significant positive correlation between the disease duration and the 2d-fALFF values in the left early visual cortex in remitting MS patients (r = 0.517, Bonferroni-corrected, p = 0.008 × 4 < 0.05). In contrast with 2d-fALFF, we detected a positive correlation between the 2d-fALFF per unit thickness of the right ventral stream visual cortex and the modified Fatigue Impact Scale (MFIS) scores (r = 0.555, Bonferroni-corrected, p = 0.017 × 4 > 0.05). For detecting MS patients, 2d-fALFF and 2d- fALFF per unit thickness both performed remarkably well in support vector machine (SVM) analysis, especially in the remitting phase (AUC = 86, 83%). Compared with 2d-fALFF, the SVM model of 2d-fALFF per unit thickness had significantly higher classification performance in distinguishing between remitting and acute MS. More changed regions and more clinically relevant 2d-fALFF per unit thickness maps in the subfrequency band were also detected in MS patients.

Conclusion

By dividing the functional value by the cortical thickness, the identification accuracy of fALFF in MS patients was detected to be potentially influenced by cortical thickness. Additionally, 2d-fALFF per unit thickness is a potential diagnostic marker that can be utilized to distinguish between acute and remitting MS patients. Notably, we observed similar variations in the subfrequency band.

Electroencephalography-Derived Functional Connectivity in Sensorimotor Networks in Post Stroke Fatigue

BACKGROUND

Poor suppression of anticipated sensory information from muscle contractions is thought to underlie high fatigue. Such diminished task-related sensory attenuation is reflected in resting state connectivity. Here we test the hypothesis 'altered electroencephalography (EEG)-derived functional connectivity in somatosensory network in the beta band, is a signature of fatigue in post-stroke fatigue'.

METHODS

In non-depressed, minimally impaired stroke survivors (n = 29), with median disease duration of 5 years, resting state neuronal activity was measured using 64-channel EEG. Graph theory-based network analysis measure of functional connectivity via small-world index (SW) was calculated focusing on right and left motor (Brodmann areas 4, 6, 8, 9, 24 and 32) and sensory (Brodmann areas 1, 2, 3, 5, 7, 40 and 43) networks, in the beta (13-30 Hz) frequency range. Fatigue was measured using Fatigue Severity Scale - FSS (Stroke), with scores of > 4, defined as high fatigue.

RESULTS

Results confirmed the working hypothesis, with high fatigue stroke survivors showing higher small-worldness in the somatosensory networks when compared to low fatigue.

CONCLUSION

High levels of small-worldness in somatosensory networks indicates altered processing of somesthetic input. Such altered processing would explain high effort perception within the sensory attenuation model of fatigue.

Functional connectome fingerprinting and stability in multiple sclerosis

Background

Functional connectome fingerprinting can identify individuals based on their functional connectome. Previous studies relied mostly on short intervals between fMRI acquisitions.

Objective

This cohort study aimed to determine the stability of connectome-based identification and their underlying signatures in patients with multiple sclerosis and healthy individuals with long follow-up intervals.

Methods

We acquired resting-state fMRI in 70 patients with multiple sclerosis and 273 healthy individuals with long follow-up times (up to 4 and 9 years, respectively). Using functional connectome fingerprinting, we examined the stability of the connectome and additionally investigated which regions, connections and networks supported individual identification. Finally, we predicted cognitive and behavioural outcome based on functional connectivity.

Results

Multiple sclerosis patients showed connectome stability and identification accuracies similar to healthy individuals, with longer time delays between imaging sessions being associated with accuracies dropping from 89% to 76%. Lesion load, brain atrophy or cognitive impairment did not affect identification accuracies within the range of disease severity studied. Connections from the fronto-parietal and default mode network were consistently most distinctive, i.e., informative of identity. The functional connectivity also allowed the prediction of individual cognitive performances.

Conclusion

Our results demonstrate that discriminatory signatures in the functional connectome are stable over extended periods of time in multiple sclerosis, resulting in similar identification accuracies and distinctive long-lasting functional connectome fingerprinting signatures in patients and healthy individuals.

Reduced clinical connectome fingerprinting in multiple sclerosis predicts fatigue severity

BACKGROUND

Brain connectome fingerprinting is progressively gaining ground in the field of brain network analysis. It represents a valid approach in assessing the subject-specific connectivity and, according to recent studies, in predicting clinical impairment in some neurodegenerative diseases. Nevertheless, its performance, and clinical utility, in the Multiple Sclerosis (MS) field has not yet been investigated.

METHODS

We conducted the Clinical Connectome Fingerprint (CCF) analysis on source-reconstructed magnetoencephalography signals in a cohort of 50 subjects: twenty-five MS patients and twenty-five healthy controls.

RESULTS

All the parameters of identifiability, in the alpha band, were reduced in patients as compared to controls. These results implied a lower similarity between functional connectomes (FCs) of the same patient and a reduced homogeneity among FCs in the MS group. We also demonstrated that in MS patients, reduced identifiability was able to predict, fatigue level (assessed by the Fatigue Severity Scale).

CONCLUSION

These results confirm the clinical usefulness of the CCF in both identifying MS patients and predicting clinical impairment. We hope that the present study provides future prospects for treatment personalization on the basis of individual brain connectome.

Distinct hemodynamic and functional connectivity features of fatigue in clinically isolated syndrome and multiple sclerosis: accounting for the confounding effect of concurrent depression symptoms

PURPOSE

This study aims to identify common and distinct hemodynamic and functional connectivity (FC) features for self-rated fatigue and depression symptoms in patients with clinically isolated syndrome (CIS) and relapsing-remitting multiple sclerosis (RR-MS).

METHODS

Twenty-four CIS, 29 RR-MS patients, and 39 healthy volunteers were examined using resting-state fMRI (rs-fMRI) to obtain whole-brain maps of (i) hemodynamic response patterns (through time shift analysis), (ii) FC (via intrinsic connectivity contrast maps), and (iii) coupling between hemodynamic response patterns and FC. Each regional map was correlated with fatigue scores, controlling for depression, and with depression scores, controlling for fatigue.

RESULTS

In CIS patients, the severity of fatigue was associated with accelerated hemodynamic response in the insula, hyperconnectivity of the superior frontal gyrus, and evidence of reduced hemodynamics-FC coupling in the left amygdala. In contrast, depression severity was associated with accelerated hemodynamic response in the right limbic temporal pole, hypoconnectivity of the anterior cingulate gyrus, and increased hemodynamics-FC coupling in the left amygdala. In RR-MS patients, fatigue was associated with accelerated hemodynamic response in the insula and medial superior frontal cortex, increased functional role of the left amygdala, and hypoconnectivity of the dorsal orbitofrontal cortex, while depression symptom severity was linked to delayed hemodynamic response in the medial superior frontal gyrus; hypoconnectivity of the insula, ventromedial thalamus, dorsolateral prefrontal cortex, and posterior cingulate; and decreased hemodynamics-FC coupling of the medial orbitofrontal cortex.

CONCLUSION

There are distinct FC and hemodynamic responses, as well as different magnitude and topography of hemodynamic connectivity coupling, associated with fatigue and depression in early and later stages of MS.

Role of selective attention in fatigue in neurological disorders

BACKGROUND

Chronic fatigue is a significant symptom in several diseases including traumatic and degenerative neurological disorders. While several studies have investigated the correlates of chronic fatigue, there is as yet no unifying framework to explain chronic fatigue.

METHODS

In this narrative review, I investigate the role of selective attention in the development of chronic fatigue and discuss results within the framework of the sensory attenuation model of fatigue, which posits that fatigue is the phenomenological output of altered attention to sensory input. Following a short introduction of this framework, I present results from investigations that address attentional mechanisms in fatigue in multiple sclerosis, stroke, traumatic brain injury and Parkinson's disease.

RESULTS

Attention was quantified in all four disease models using a variety of outcome measures, including behavioural, neurophysiological, structural and functional brain connectivity. The range of measures precluded direct comparison of results across disease conditions; however, in all four disease models there was evidence of poor selective attention that explained levels of chronic fatigue, supporting the sensory attenuation model of fatigue as a disease-independent mechanism of fatigue. Evidence was lacking to draw any conclusions about the direction of causality.

CONCLUSION

The role of selective attention in development of fatigue is indicated. Future studies must focus on establishing causality and exploring attentional circuitry as a potential therapeutic target.

Structural brain changes in patients with post-COVID fatigue: a prospective observational study

BACKGROUND

Post-COVID syndrome is a severe long-term complication of COVID-19. Although fatigue and cognitive complaints are the most prominent symptoms, it is unclear whether they have structural correlates in the brain. We therefore explored the clinical characteristics of post-COVID fatigue, describe associated structural imaging changes, and determine what influences fatigue severity.

METHODS

We prospectively recruited 50 patients from neurological post-COVID outpatient clinics (age 18-69 years, 39f/8m) and matched non-COVID healthy controls between April 15 and December 31, 2021. Assessments included diffusion and volumetric MR imaging, neuropsychiatric, and cognitive testing. At 7.5 months (median, IQR 6.5-9.2) after the acute SARS-CoV-2 infection, moderate or severe fatigue was identified in 47/50 patients with post-COVID syndrome who were included in the analyses. As a clinical control group, we included 47 matched multiple sclerosis patients with fatigue.

FINDINGS

Our diffusion imaging analyses revealed aberrant fractional anisotropy of the thalamus. Diffusion markers correlated with fatigue severity, such as physical fatigue, fatigue-related impairment in everyday life (Bell score) and daytime sleepiness. Moreover, we observed shape deformations and decreased volumes of the left thalamus, putamen, and pallidum. These overlapped with the more extensive subcortical changes in MS and were associated with impaired short-term memory. While fatigue severity was not related to COVID-19 disease courses (6/47 hospitalised, 2/47 with ICU treatment), post-acute sleep quality and depressiveness emerged as associated factors and were accompanied by increased levels of anxiety and daytime sleepiness.

INTERPRETATION

Characteristic structural imaging changes of the thalamus and basal ganglia underlie the persistent fatigue experienced by patients with post-COVID syndrome. Evidence for pathological changes to these subcortical motor and cognitive hubs provides a key to the understanding of post-COVID fatigue and related neuropsychiatric complications.

FUNDING

Deutsche Forschungsgemeinschaft (DFG) and German Ministry of Education and Research (BMBF).

Structural and functional magnetic resonance imaging correlates of fatigue and dual-task performance in progressive multiple sclerosis

BACKGROUND

Frontal cortico-subcortical dysfunction may contribute to fatigue and dual-task impairment of walking and cognition in progressive multiple sclerosis (PMS).

PURPOSE

To explore the associations among fatigue, dual-task performance and structural and functional abnormalities of frontal cortico-subcortical network in PMS.

METHODS

Brain 3 T structural and functional MRI sequences, Modified Fatigue Impact Scale (MFIS), dual-task motor and cognitive performances were obtained from 57 PMS patients and 10 healthy controls (HC). The associations of thalamic, caudate nucleus and dorsolateral prefrontal cortex (DLPFC) atrophy, microstructural abnormalities of their connections and their resting state effective connectivity (RS-EC) with fatigue and dual-task performance were investigated using random forest.

RESULTS

Thirty-seven PMS patients were fatigued (F) (MFIS ≥ 38). Compared to HC, non-fatigued (nF) and F-PMS patients had significantly worse dual-task performance (p ≤ 0.002). Predictors of fatigue (out-of-bag [OOB]-accuracy = 0.754) and its severity (OOB-R² = 0.247) were higher Expanded Disability Status scale (EDSS) score, lower RS-EC from left-caudate nucleus to left-DLPFC, lower fractional anisotropy between left-caudate nucleus and left-thalamus, higher mean diffusivity between right-caudate nucleus and right-thalamus, and longer disease duration. Microstructural abnormalities in connections among thalami, caudate nuclei and DLPFC, mainly left-lateralized in nF-PMS and more bilateral in F-PMS, higher RS-EC from left-DLPFC to right-DLPFC in nF-PMS and lower RS-EC from left-caudate nucleus to left-DLPFC in F-PMS, higher EDSS score, higher WM lesion volume, and lower cortical volume predicted worse dual-task performances (OOB-R² from 0.426 to 0.530).

CONCLUSIONS

In PMS, structural and functional frontal cortico-subcortical abnormalities contribute to fatigue and worse dual-task performance, with different patterns according to the presence of fatigue.

Monoaminergic network abnormalities: a marker for multiple sclerosis-related fatigue and depression

OBJECTIVE

To investigate monoaminergic network abnormalities in patients with multiple sclerosis (MS) according to their fatigue and depressive status through a positron emission tomography (PET)-based constrained independent component analysis (ICA) on resting state (RS) functional MRI (fMRI).

METHODS

In this prospective study, 213 patients with MS (mean age=40.6±12.5 years; 94/119 men/women; 153 relapsing-remitting; 60 progressive) and 62 healthy controls (HCs, mean age=39.0±10.4 years; 30/32 men/women) underwent neurological, fatigue, depression and RS fMRI assessment. Patterns of dopamine, norepinephrine-related and serotonin-related RS functional connectivity (FC) were derived by ICA, constrained to PET atlases for dopamine, norepinephrine and serotonin transporters, obtained in HCs' brain.

RESULTS

Compared with HCs, patients with MS showed abnormalities in all three explored monoaminergic networks, mostly with decreased RS FC within PET-guided monoaminergic networks in frontal regions and subcortical areas including the cerebellum and thalamus, and increased RS FC in temporo-parieto-occipital cortical areas, including bilateral precunei.MS-related fatigue was associated with decreased RS FC within the PET-guided dopamine network in the left thalamus and left cerebellum, and with increased RS FC within the PET-guided serotonin network in the left middle occipital gyrus. MS-related depression was associated with more distributed abnormalities involving the three explored monoaminergic networks, resulting in overall reduced RS FC in the frontal lobe, limbic areas and the precuneus.

CONCLUSIONS

Patients with MS present diffuse dysregulation in the monoaminergic networks. Specific alterations in these networks were associated with fatigue and depression, providing a pathological marker for these bothersome symptoms and putative targets for their treatment.

The borderland of multiple sclerosis and functional neurological disorder: A call for clinical research and vigilance

BACKGROUND AND PURPOSE

Functional neurological disorders (FNDs) have attracted much attention from the neurological medical community over the last decades as new developments in neurosciences have reduced stigma around these by showing brain network dysfunctions. An overlap with other neurological conditions such as multiple sclerosis (MS) is well known by clinicians but there is a lack of clinical and fundamental research in this field to better define diagnosis and therapeutic decisions, as well as a lack of deep understanding of the underlying pathophysiology.

AIM

We aimed to provide a critical commentary on the state of knowledge about the borderland between FNDs and MS.

METHODS

We based our commentary on a joint point of view between an FND specialist and an MS expert.

RESULTS

A brief review of the previous literature and relevant new studies covering the overlap between FNDs and MS is presented, along with suggestions for future research directions.

CONCLUSION

There are clear diagnostic criteria for both FNDs and MS and a strict application of these will help better diagnosis and prevent unnecessary treatment escalation in MS or absence of referral to multimodal therapy in FND. Better teaching of younger neurologists is needed as well as prospective research focusing on pathophysiology.

Altered functional connectivity during performance feedback processing in multiple sclerosis

Effective learning from performance feedback is vital for adaptive behavior regulation necessary for successful cognitive performance. Yet, how this learning operates in clinical groups that experience cognitive dysfunction is not well understood. Multiple sclerosis (MS) is an autoimmune, degenerative disease of the central nervous system characterized by physical and cognitive dysfunction. A highly prevalent impairment in MS is cognitive fatigue (CF). CF is associated with altered functioning within cortico-striatal regions that also facilitate feedback-based learning in neurotypical (NT) individuals. Despite this cortico-striatal overlap, research about feedback-based learning in MS, its associated neural underpinnings, and its sensitivity to CF, are all lacking. The present study investigated feedback-based learning ability in MS, as well as associated cortico-striatal function and connectivity. MS and NT participants completed a functional magnetic resonance imaging (fMRI) paired-word association task during which they received trial-by-trial monetary, non-monetary, and uninformative performance feedback. Despite reporting greater CF throughout the task, MS participants displayed comparable task performance to NTs, suggesting preserved feedback-based learning ability in the MS group. Both groups recruited the ventral striatum (VS), caudate nucleus, and ventromedial prefrontal cortex in response to the receipt of performance feedback, suggesting that people with MS also recruit cortico-striatal regions during feedback-based learning. However, compared to NT participants, MS participants also displayed stronger functional connectivity between the VS and task-relevant regions, including the left angular gyrus and right superior temporal gyrus, in response to feedback receipt. Results indicate that CF may not interfere with feedback-based learning in MS. Nonetheless, people with MS may recruit alternative connections with the striatum to assist with this form of learning. These findings have implications for cognitive rehabilitation treatments that incorporate performance feedback to remediate cognitive dysfunction in clinical populations.

Increased flexibility of brain dynamics in patients with multiple sclerosis

Patients with multiple sclerosis consistently show widespread changes in functional connectivity. Yet, alterations are heterogeneous across studies, underscoring the complexity of functional reorganization in multiple sclerosis. Here, we aim to provide new insights by applying a time-resolved graph-analytical framework to identify a clinically relevant pattern of dynamic functional connectivity reconfigurations in multiple sclerosis. Resting-state data from 75 patients with multiple sclerosis (N = 75, female:male ratio of 3:2, median age: 42.0 ± 11.0 years, median disease duration: 6 ± 11.4 years) and 75 age- and sex-matched controls (N = 75, female:male ratio of 3:2, median age: 40.2 ± 11.8 years) were analysed using multilayer community detection. Local, resting-state functional system and global levels of dynamic functional connectivity reconfiguration were characterized using graph-theoretical measures including flexibility, promiscuity, cohesion, disjointedness and entropy. Moreover, we quantified hypo- and hyper-flexibility of brain regions and derived the flexibility reorganization index as a summary measure of whole-brain reorganization. Lastly, we explored the relationship between clinical disability and altered functional dynamics. Significant increases in global flexibility (t = 2.38, P_FDR = 0.024), promiscuity (t = 1.94, P_FDR = 0.038), entropy (t = 2.17, P_FDR = 0.027) and cohesion (t = 2.45, P_FDR = 0.024) were observed in patients and were driven by pericentral, limbic and subcortical regions. Importantly, these graph metrics were correlated with clinical disability such that greater reconfiguration dynamics tracked greater disability. Moreover, patients demonstrate a systematic shift in flexibility from sensorimotor areas to transmodal areas, with the most pronounced increases located in regions with generally low dynamics in controls. Together, these findings reveal a hyperflexible reorganization of brain activity in multiple sclerosis that clusters in pericentral, subcortical and limbic areas. This functional reorganization was linked to clinical disability, providing new evidence that alterations of multilayer temporal dynamics play a role in the manifestation of multiple sclerosis.

Functional connectivity dynamics reflect disability and multi-domain clinical impairment in patients with relapsing-remitting multiple sclerosis

BACKGROUND & AIM

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system associated with deficits in cognitive and motor functioning. While structural brain changes such as demyelination are an early hallmark of the disease, a characteristic profile of functional brain alterations in early MS is lacking. Functional neuroimaging studies at various disease stages have revealed complex and heterogeneous patterns of aberrant functional connectivity (FC) in MS, with previous studies largely being limited to a static account of FC. Thus, it remains unclear how time-resolved FC relates to variance in clinical disability status in early MS. We here aimed to characterize brain network organization in early MS patients with time-resolved FC analysis and to explore the relationship between disability status, multi-domain clinical outcomes and altered network dynamics.

METHODS

Resting-state functional MRI (rs-fMRI) data were acquired from 101 MS patients and 101 age- and sex-matched healthy controls (HC). Based on the Expanded Disability Status Score (EDSS), patients were split into two sub-groups: patients without clinical disability (EDSS ≤ 1, n = 36) and patients with mild to moderate levels of disability (EDSS ≥ 2, n = 39). Five dynamic FC states were extracted from whole-brain rs-fMRI data. Group differences in static and dynamic FC strength, across-state overall connectivity, dwell time, transition frequency, modularity, and global connectivity were assessed. Patients' impairment was quantified as custom clinical outcome z-scores (higher: worse) for the domains depressive symptoms, fatigue, motor, vision, cognition, total brain atrophy, and lesion load. Correlation analyses between functional measures and clinical outcomes were performed with Spearman partial correlation analyses controlling for age.

RESULTS

Patients with mild to moderate levels of disability exhibited a more widespread spatiotemporal pattern of altered FC and spent more time in a high-connectivity, low-occurrence state compared to patients without disability and HCs. Worse symptoms in all clinical outcome domains were positively associated with EDSS scores. Furthermore, depressive symptom severity was positively related to functional dynamics as measured by state-specific global connectivity and default mode network connectivity with attention networks, while fatigue and motor impairment were related to reduced frontoparietal network connectivity with the basal ganglia.

CONCLUSIONS

Despite comparably low impairment levels in early MS, we identified distinct connectivity alterations between patients with mild to moderate disability and those without disability, and these changes were sensitive to clinical outcomes in multiple domains. Furthermore, time-resolved analysis uncovered alterations in network dynamics and clinical correlations that remained undetected with conventional static analyses, showing that accounting for temporal dynamics helps disentangle the relationship between functional alterations, disability status, and symptoms in early MS.

Current perspectives on the diagnosis and management of fatigue in multiple sclerosis

INTRODUCTION

Fatigue is a common and debilitating symptom among multiple sclerosis (MS) patients with a prevalence up to 81% and with a considerable impact on quality of life. However, its subjective nature makes it difficult to define and quantify in clinical practice. Research aimed at a more precise definition and knowledge of this construct is thus continuously growing.

AREAS COVERED

This review summarizes the most relevant updates available on PubMed up to July 1^st 2022 regarding: the assessment methods that aim to measure the concept of fatigue (as opposed to fatigability), the possible treatment pathways currently available to clinicians, interconnection with the pathophysiological substrates and with the common comorbidities of MS, such as depression and mood disorders.

EXPERT OPINION

The in-depth study of fatigue can help to better understand its actual impact on MS patients and can stimulate clinicians towards a more valid approach, through a targeted analysis of this symptom. Considering fatigue from a multidimensional perspective allows the use of patient-tailored methods for its identification and subsequent treatment by different professional figures. Better identification of methods and treatment pathways would reduce the extremely negative impact of fatigue on MS patients' quality of life.

Neural distinctiveness of fatigue and low sleep quality in multiple sclerosis

BACKGROUND AND PURPOSE

Fatigue and low sleep quality in multiple sclerosis (MS) are closely related symptoms. Here, the associations between the brain's functional connectivity (FC) and fatigue and low sleep quality were investigated to determine the degree of neural distinctiveness of these symptoms.

METHOD

A hundred and four patients with relapsing-remitting MS (age 38.9 ± 10.2 years, 66 females) completed the Modified Fatigue Impact Scale and the Pittsburgh Sleep Quality Index and underwent resting-state functional magnetic resonance imaging. FC was analyzed using independent-component analysis in sensorimotor, default-mode, fronto-parietal and basal-ganglia networks. Multiple linear regression models allowed us to test the association between FC and fatigue and sleep quality whilst controlling for one another as well as for demographic, disease-related and imaging variables.

RESULTS

Higher fatigue correlated with lower sleep quality (r = 0.54, p < 0.0001). Higher fatigue was associated with lower FC of the precentral gyrus in the sensorimotor network, the precuneus in the posterior default-mode network and the superior frontal gyrus in the left fronto-parietal network, independently of sleep quality. Lower sleep quality was associated with lower FC of the left intraparietal sulcus in the left fronto-parietal network, independently of fatigue. Specific associations were found between fatigue and the sensorimotor network's global FC and between low sleep quality and the left fronto-parietal network's global FC.

CONCLUSION

Despite the high correlation between fatigue and low sleep quality in the clinical picture, our findings clearly indicate that, on the neural level, fatigue and low sleep quality in MS are associated with decreased FC in distinct functional brain networks.

Symptom Interconnectivity in Multiple Sclerosis: A Narrative Review of Potential Underlying Biological Disease Processes

Introduction

Fatigue, cognitive impairment, depression, and pain are highly prevalent symptoms in multiple sclerosis (MS). These often co-occur and may be explained by a common etiology. By reviewing existing literature, we aimed to identify potential underlying biological processes implicated in the interconnectivity between these symptoms.

Methods

A literature search was conducted to identify articles reporting research into the biological mechanisms responsible for the manifestation of fatigue, cognitive impairment, depression, and pain in MS. PubMed was used to search for articles published from July 2011 to July 2021. We reviewed and assessed findings from the literature to identify biological processes common to the symptoms of interest.

Results

Of 693 articles identified from the search, 252 were selected following screening of titles and abstracts and assessing reference lists of review articles. Four biological processes linked with two or more of the symptoms of interest were frequently identified from the literature: (1) direct neuroanatomical changes to brain regions linked with symptoms of interest (e.g., thalamic injury associated with cognitive impairment, fatigue, and depression), (2) pro-inflammatory cytokines associated with so-called ‘sickness behavior,’ including manifestation of fatigue, transient cognitive impairment, depression, and pain, (3) dysregulation of monoaminergic pathways leading to depressive symptoms and fatigue, and (4) hyperactivity of the hypothalamic–pituitary-adrenal (HPA) axis as a result of pro-inflammatory cytokines promoting the release of brain noradrenaline, serotonin, and tryptophan, which is associated with symptoms of depression and cognitive impairment.

Conclusion

The co-occurrence of fatigue, cognitive impairment, depression, and pain in MS appears to be associated with a common set of etiological factors, namely neuroanatomical changes, pro-inflammatory cytokines, dysregulation of monoaminergic pathways, and a hyperactive HPA axis. This association of symptoms and biological processes has important implications for disease management strategies and, eventually, could help find a common therapeutic pathway that will impact both inflammation and neuroprotection.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40120-022-00368-2.

Brain Under Fatigue – Can Perceived Fatigability in Multiple Sclerosis Be Seen on the Level of Functional Brain Network Architecture?

Background

Fatigue is one of the most common symptoms of multiple sclerosis (MS), significantly affecting the functioning of the patients. However, the neural underpinnings of physical and mental fatigue in MS are still vague. The aim of our study was to investigate the functional architecture of resting-state networks associated with fatigue in patients with MS.

Methods

The sum of 107 high-functioning patients underwent a resting-state scanning session and filled out the 9-item Fatigue Severity Scale (FSS). Based on the FSS score, we identified patients with different levels of fatigue using the cluster analysis. The low-fatigue group consisted of n = 53 subjects, while the high-fatigue group n = 48. The neuroimaging data were analyzed in terms of functional connectivity (FC) between various resting-state networks as well as amplitude of low-frequency fluctuation (ALFF) and fractional amplitude of low-frequency fluctuations (fALFF).

Results

Two-sample t-test revealed between-group differences in FC of posterior salience network (SN). No differences occurred in default mode network (DMN) and sensorimotor network (SMN). Moreover, differences in fALFF were shown in the right middle frontal gyrus and right superior frontal gyrus, however, no ALFF differences took place.

Conclusion

Current study revealed significant functional network (FN) architecture between-group differences associated with fatigue. Present results suggest the higher level of fatigue is related to deficits in awareness as well as higher interoceptive awareness and nociception.

Multiple sclerosis-related fatigue lacks a unified definition: A narrative review

Fatigue is the most common symptom in multiple sclerosis (MS). Although MS-related fatigue (MS-F) strongly affects quality of life and social performance of patients, there is currently a lack of knowledge about its pathophysiology, which in turns leads to poor objective diagnosis and management. Recent studies have attempted to explain potential etiologies as well as treatments for MS-F. However, it seems that without a consensus on its nature, these data could not provide a route to a successful approach. In this Article, we review definitions, epidemiology, risk factors and correlated comorbidities, pathophysiology, assessment methods, neuroimaging findings, and pharmacological and nonpharmacological treatments of MS-F. Further studies are warranted to define fatigue in MS patients more accurately, which could result in precise diagnosis and management.

Effects of non-invasive brain stimulation in multiple sclerosis: systematic review and meta-analysis

Objective:

The objective of this meta-analysis was to summarize evidence on the therapeutic effects of non-invasive brain stimulation (NIBS) on core symptoms of multiple sclerosis (MS). Specifically, findings from studies deploying transcranial direct current stimulation (tDCS) and repetitive transcranial magnetic stimulation (rTMS) protocols were summarized in this review.

Methods:

We systematically searched articles published in four databases, until 31 May 2021, which compared the effects of active tDCS or rTMS with sham intervention in MS patients. We used a random-effects model for this meta-analysis. Meta-regression and subgroup meta-analysis were used to examine the effects of stimulation dose and different stimulation protocols, respectively.

Results:

Twenty-five randomized controlled trials (RCTs) were included in this review, consisting of 19 tDCS and 6 rTMS studies. tDCS led to a significant and immediate reduction of fatigue with a large effect size (Hedges’s g = −0.870, 95% confidence intervals (CI) = [−1.225 to −0.458], number needed to treat (NNT) = 2). Particularly, a subgroup analysis showed that applying tDCS over the left DLPFC and bilateral S1 led to fatigue reductions compared to sham stimulation. Furthermore, tDCS had favorable effects on fatigue in MS patients with low physical disability but not those with high physical disability, and additionally improved cognitive function. Finally, whereas rTMS was observed to reduce muscle spasticity, these NIBS protocols showed no further effect on MS-associated pain and mood symptoms.

Conclusion:

tDCS in MS alleviates fatigue and improves cognitive function whereas rTMS reduces muscle spasticity. More high-quality studies are needed to substantiate the therapeutic effects of different NIBS protocols in MS.

Subcortical volumes as early predictors of fatigue in multiple sclerosis

OBJECTIVE

Fatigue is a frequent and severe symptom in multiple sclerosis (MS), but its pathophysiological origin remains incompletely understood. We aimed to examine the predictive value of subcortical gray matter volumes for fatigue severity at disease onset and after four years by applying structural equation modeling (SEM).

METHODS

This multi-center cohort study included 601 treatment-naive MS patients after the first demyelinating event. All patients underwent a standardized 3T MRI protocol. A subgroup of 230 patients with available clinical follow-up data after four years was also analyzed. Associations of subcortical volumes (included into SEM) with MS-related fatigue were studied regarding their predictive value. In addition, subcortical regions that have a central role in the brain network (hubs) were determined through structural covariance network (SCN) analysis.

RESULTS

Predictive causal modeling identified volumes of the caudate (s [standardized path coefficient]=0.763, p=0.003 [left]; s=0.755, p=0.006 [right]), putamen (s=0.614, p=0.002 [left]; s=0.606, p=0.003 [right]) and pallidum (s=0.606, p=0.012 [left]; s=0.606, p=0.012 [right]) as prognostic factors for fatigue severity in the cross-sectional cohort. Moreover, the volume of the pons was additionally predictive for fatigue severity in the longitudinal cohort (s=0.605, p=0.013). In the SCN analysis, network hubs in patients with fatigue worsening were detected in the putamen (p=0.008 [left]; p=0.007 [right]) and pons (p=0.0001).

INTERPRETATION

We unveiled predictive associations of specific subcortical gray matter volumes with fatigue in an early and initially untreated MS cohort. The colocalization of these subcortical structures with network hubs suggests an early role of these brain regions in terms of fatigue evolution. This article is protected by copyright. All rights reserved.

Carbohydrate and lipid metabolism in multiple sclerosis: Clinical implications for etiology, pathogenesis, diagnosis, prognosis, and therapy

Multiple sclerosis (MS) is a complicated autoimmune disease characterized by inflammatory and demyelinating events in the central nervous system. The exact etiology and pathogenesis of MS have not been elucidated. However, a set of metabolic changes and their effects on immune cells and neural functions have been explained. This review highlights the contribution of carbohydrates and lipids metabolism to the etiology and pathogenesis of MS. Then, we have proposed a hypothetical relationship between such metabolic changes and the immune system in patients with MS. Finally, the potential clinical implications of these metabolic changes in diagnosis, prognosis, and discovering therapeutic targets have been discussed. It is concluded that research on the pathophysiological alterations of carbohydrate and lipid metabolism may be a potential strategy for paving the way toward MS treatment.

Morphological profiles of fatigue in Sarcoidosis patients

INTRODUCTION

Sarcoidosis is a chronic inflammatory disease often associated with chronic fatigue. Prevalence of fatigue can be measured via neuropsychological testing. Its pathophysiology is insufficiently understood. Structural analysis might help with the development of novel treatment methods.

METHODS

We recruited 30 sarcoidosis patients whose fatigue severity and depressive symptom presence was measured through validated neuropsychological self-assessment. T1-weighted structural images were acquired and VBM preprocessing was conducted. Total scores of these tests and subscales were correlated through multiple regression analysis to the brain morphometry.

RESULTS

Fatigue severity positively correlated with gray matter volumes in the striatum, the cingulate cortex and the cerebellum and negatively in the parietal and temporal lobe and posterior insula. Subscale analysis indicated a correlation between cognitive fatigue and striatum involvement as well as between physical and psychosocial fatigue and cerebellar alterations.

DISCUSSION

Structural analysis delineated two structural patterns associated with the presence of fatigue. One such pattern mainly seemed to involve structures with a focus on decision-making processes while the other indicated alterations in regions vital for perception. Fatigue seems to be a heterogeneous disease, where varying dimensions of reported symptoms correlate with different patterns of structural changes.

Distinguishing between Fatigue and Fatigability in Multiple Sclerosis

Fatigue is one of the most common debilitating symptoms reported by persons with multiple sclerosis (MS). It reflects feelings of tiredness, lack of energy, low motivation, and difficulty in concentrating. It can be measured at a specific instant in time as a perception that arises from interoceptive networks involved in the regulation of homeostasis. Such ratings indicate the state level of fatigue and likely reflect an inability to correct deviations from a balanced homeostatic state. In contrast, the trait level of fatigue is quantified in terms of work capacity (fatigability), which can be either estimated (perceived fatigability) or measured (objective fatigability). Clinically, fatigue is most often quantified with questionnaires that require respondents to estimate their past capacity to perform several cognitive, physical, and psychosocial tasks. These retrospective estimates provide a measure of perceived fatigability. In contrast, the change in an outcome variable during the actual performance of a task provides an objective measure of fatigability. Perceived and objective fatigability do not assess the same underlying construct. Persons with MS who report elevated trait levels of fatigue exhibit deficits in interoceptive networks (insula and dorsal anterior cingulate cortex), including increased functional connectivity during challenging tasks. The state and trait levels of fatigue reported by an individual can be modulated by reward and pain pathways. Understanding the distinction between fatigue and fatigability is critical for the development of effective strategies to reduce the burden of the symptom for individuals with MS.

Mild parkinsonian signs, energy decline, and striatal volume in community-dwelling older adults

BACKGROUND

Mild Parkinsonian Signs (MPS), highly prevalent in older adults, predict disability. It is unknown whether energy decline, a predictor of mobility disability, is also associated with MPS. We hypothesized that those with MPS had greater decline in self-reported energy levels (SEL) than those without MPS, and that SEL decline and MPS share neural substrates.

METHODS

Using data from the Health, Aging and Body Composition Study, we analyzed 293 Parkinson's Disease-free participants (83±3 years old, 39% Black, 58% women) with neuroimaging data, MPS evaluation by Unified Parkinson Disease Rating Scale in 2006-2008, and ≥ 3 measures of SEL since 1999-2000. Individual SEL slopes were computed via linear mixed models. Associations of SEL slopes with MPS were tested using logistic regression models. Association of SEL slope with volume of striatum, sensorimotor, and cognitive regions were examined using linear regression models adjusted for normalized total gray matter volume. Models were adjusted for baseline SEL, mobility, demographics, and comorbidities.

RESULTS

Compared to those without MPS (n=165), those with MPS (n=128) had 37% greater SEL decline in the prior eight years (p=0.001). Greater SEL decline was associated with smaller right striatal volume (adjusted standardized β=0.126, p=0.029). SEL decline was not associated with volumes in other regions. The association of SEL decline with MPS remained similar after adjustment for right striatal volume (adjusted OR=2.03, 95% CI: 1.16 - 3.54).

CONCLUSION

SEL decline may be faster in those with MPS. Striatal atrophy may be important for declining energy but does not explain the association with MPS.

Neurostructural and Neurophysiological Correlates of Multiple Sclerosis Physical Fatigue: Systematic Review and Meta-Analysis of Cross-Sectional Studies

Fatigue is one of the most debilitating symptoms for people with multiple sclerosis (PwMS). By consolidating a diverse and conflicting evidence-base, this systematic review and meta-analysis aimed to gain new insights into the neurobiology of MS fatigue. MEDLINE, ProQuest, CINAHL, Web of Science databases and grey literature were searched using Medical Subject Headings. Eligible studies compared neuroimaging and neurophysiological data between people experiencing high (MS-HF) versus low (MS-LF) levels of perceived MS fatigue, as defined by validated fatigue questionnaire cut-points. Data were available from 66 studies, with 46 used for meta-analyses. Neuroimaging studies revealed lower volumetric measures in MS-HF versus MS-LF for whole brain (-22.74 ml; 95% CI: -37.72 to -7.76 ml; p = 0.003), grey matter (-18.81 ml; 95% CI: -29.60 to -8.03 ml; p < 0.001), putamen (-0.40 ml; 95% CI: -0.69 to -0.10 ml; p = 0.008) and acumbens (-0.09 ml; 95% CI: -0.15 to -0.03 ml; p = 0.003) and a higher volume of T1-weighted hypointense lesions (1.10 ml; 95% CI: 0.47 to 1.73 ml; p < 0.001). Neurophysiological data showed reduced lower-limb maximum voluntary force production (-19.23 N; 95% CI: -35.93 to -2.53 N; p = 0.02) and an attenuation of upper-limb (-5.77%; 95% CI:-8.61 to -2.93%; p < 0.0001) and lower-limb (-2.16%; 95% CI:-4.24 to -0.07%; p = 0.04) skeletal muscle voluntary activation, accompanied by more pronounced upper-limb fatigability (-5.61%; 95% CI: -9.57 to -1.65%; p = 0.006) in MS-HF versus MS-LF. Results suggest that MS fatigue is characterised by greater cortico-subcortical grey matter atrophy and neural lesions, accompanied by neurophysiological decrements, which include reduced strength and voluntary activation. Prospero registration Prospero registration number: CRD42016017934.

Alterations in functional connectivity are associated with white matter lesions and information processing efficiency in multiple sclerosis

Functional connectivity (FC) is typically altered in individuals with Multiple Sclerosis (MS). However, in relapsing-remitting multiple sclerosis (RRMS) patients, the relationship between brain FC, tissue integrity and cognitive impairment is still unclear as contradictory findings have been documented. In this exploratory study we compared both the whole brain connectome and resting state networks (RSNs) FC of twenty-one RRMS and seventeen healthy controls (HCs), using combined network based statistics and independent component analyses. The total white matter (WM) lesion volume and information processing efficiency were also correlated with FC in the RRMS group. Both whole brain connectome and individual RSNs FC were diminished in patients with RRMS compared to HC. Additionally, the reduction in FC was found to be a function of the total WM lesion volume, with greatest impact in those harboring the largest lesion volume. Finally, a positive correlation between FC and information processing efficiency was observed in RRMS. This complimentary whole brain and RSNs FC approach can contribute to clarify literature inconsistencies regarding FC alterations and provide new insights on the white matter structural damage in explaining functional abnormalities in RRMS.

Cortico-subcortical functional connectivity modifications in fatigued multiple sclerosis patients treated with fampridine and amantadine

BACKGROUND AND PURPOSE

Fatigue in multiple sclerosis (MS) is common and disabling; medication efficacy is still not fully proven. The aim of this study was to investigate 4-week modifications of fatigue severity in 45 relapsing-remitting MS patients after different symptomatic treatments, and changes in concomitant resting state (RS) functional connectivity (FC).

METHODS

Patients were randomly, blindly assigned to treatment with fampridine (n = 15), amantadine (n = 15) or placebo (n = 15), and underwent clinical assessment and 3-Tesla RS functional magnetic resonance imaging at baseline (t0) and after 4 weeks (w4) of treatment. Fifteen healthy controls (HCs) were also studied. Changes in modified fatigue impact scale (MFIS) score and network RS FC were assessed.

RESULTS

In MS, abnormalities of network RS FC at t0 did not differ between treatment groups and correlated with fatigue severity. At w4, global scores and subscores on the MFIS decreased in all groups, with no time-by-treatment interaction. At w4, all patient groups had changes in RS FC in several networks, with significant time-by-treatment interactions in basal ganglia, sensorimotor and default-mode networks in fampridine-treated patients versus the other groups, and in frontoparietal network in amantadine-treated patients. In the fampridine group, RS FC changes correlated with concurrently decreased MFIS score (r range = -0.75 to 0.74, p range = 0.003-0.05).

CONCLUSIONS

Fatigue improved in all MS groups, independently of treatment. Concomitant RS FC modifications were located in sensorimotor, inferior frontal and subcortical regions for fampridine- and amantadine-treated patients, and in associative sensory cortices for placebo-treated patients.

Quantitative spinal cord MRI in MOG-antibody disease, neuromyelitis optica and multiple sclerosis

Spinal cord involvement is a hallmark feature of multiple sclerosis, neuromyelitis optica with AQP4 antibodies and MOG-antibody disease. In this cross-sectional study we use quantitative spinal cord MRI to better understand these conditions, differentiate them and associate with relevant clinical outcomes. Eighty participants (20 in each disease group and 20 matched healthy volunteers) underwent spinal cord MRI (cervical cord: 3D T1, 3D T2, diffusion tensor imaging and magnetization transfer ratio; thoracic cord: 3D T2), together with disability, pain and fatigue scoring. All participants had documented spinal cord involvement and were at least 6 months post an acute event. MRI scans were analysed using publicly available software. Those with AQP4-antibody disease showed a significant reduction in cervical cord cross-sectional area (P = 0.038), thoracic cord cross-sectional area (P = 0.043), cervical cord grey matter (P = 0.011), magnetization transfer ratio (P ≤ 0.001), fractional anisotropy (P = 0.004) and increased mean diffusivity (P = 0.008). Those with multiple sclerosis showed significantly increased mean diffusivity (P = 0.001) and reduced fractional anisotropy (P = 0.013), grey matter volume (P = 0.002) and magnetization transfer ratio (P = 0.011). In AQP4-antibody disease the damage was localized to areas of the cord involved in the acute attack. In multiple sclerosis this relationship with lesions was absent. MOG-antibody disease did not show significant differences to healthy volunteers in any modality. However, when considering only areas involved at the time of the acute attack, a reduction in grey matter volume was found (P = 0.023). This suggests a predominant central grey matter component to MOG-antibody myelitis, which we hypothesize could be partially responsible for the significant residual sphincter dysfunction. Those with relapsing MOG-antibody disease showed a reduction in cord cross-sectional area compared to those with monophasic disease, even when relapses occurred elsewhere (P = 0.012). This suggests that relapsing MOG-antibody disease is a more severe phenotype. We then applied a principal component analysis, followed by an orthogonal partial least squares analysis. MOG-antibody disease was discriminated from both AQP4-antibody disease and multiple sclerosis with moderate predictive values. Finally, we assessed the clinical relevance of these metrics using a multiple regression model. Cervical cord cross-sectional area associated with disability scores (B = -0.07, P = 0.0440, R2 = 0.20) and cervical cord spinothalamic tract fractional anisotropy associated with pain scores (B = -19.57, P = 0.016, R2 = 0.55). No spinal cord metric captured fatigue. This work contributes to our understanding of myelitis in these conditions and highlights the clinical relevance of quantitative spinal cord MRI.

Effectiveness of massage therapy on fatigue and pain in patients with multiple sclerosis: A systematic review and meta-analysis

BACKGROUND

Fatigue and pain are prevalent symptoms of multiple sclerosis (MS) and frequent complaint in MS patients, which reduce their quality of life. This study aimed to assess the effect of massage therapy on pain and fatigue in MS Patients.

METHOD

The original and Persian databases were searched included PubMed, web of science, embase, ovid, scopus, and the Cochrane Library, SID, and Iranedex from inception to November 2020. Studies that reported the effect of massage on fatigue and pain were included. Two investigators extracted all relevant data, independently. For deriving analysis, mean difference (MD) and standardized mean difference (SMD) were used.

RESULT

Ten studies were eligible acoording criteria. The effect of massage on fatigue showed significant improvement (-1.62; 95% CL -2.40, -0.83; p < .00001), also results of the systematic review showed a significant reduction in pain severity.

CONCLUSION

Massage as a complementary and non-pharmacological therapy might have been associated with alleviating fatigue and pain in M.S. patients. Based on the current study, massage intervention for MS patients could have possible clinical value for palliating pain and fatigue and improving quality of life; however, this matter needs further and more significant trial studies.

Transcranial magnetic stimulation (TMS) and repetitive TMS in multiple sclerosis

Multiple sclerosis (MS) is the most well-known autoimmune disorder of the central nervous system, and constitutes a major cause of disability, especially in young individuals. A wide array of pharmacological treatments is available, but they have often been proven to be ineffective in ameliorating disease symptomatology or slowing disease progress. As such, non-invasive and non-pharmacological techniques have been gaining more ground. Transcranial magnetic stimulation (TMS) utilizes the electric field generated by a magnetic coil to stimulate neurons and has been applied, usually paired with electroencephalography, to study the underlying pathophysiology of MS, and in repetitive trains, in the form of repetitive transcranial magnetic stimulation (rTMS), to induce long-lasting changes in neuronal circuits. In this review, we present the available literature on the application of TMS and rTMS in the context of MS, with an emphasis on its therapeutic potential on various clinical aspects, while also naming the ongoing trials, whose results are anticipated in the future.

Disruption of brainstem monoaminergic fibre tracts in multiple sclerosis as a putative mechanism for cognitive fatigue: a fixel-based analysis

In multiple sclerosis (MS), monoaminergic systems are altered as a result of both inflammation-dependent reduced synthesis and direct structural damage. Aberrant monoaminergic neurotransmission is increasingly considered a major contributor to fatigue pathophysiology. In this study, we aimed to compare the integrity of the monoaminergic white matter fibre tracts projecting from brainstem nuclei in a group of patients with MS (n = 68) and healthy controls (n = 34), and to investigate its association with fatigue. Fibre tracts integrity was assessed with the novel fixel-based analysis that simultaneously estimates axonal density, by means of 'fibre density', and white matter atrophy, by means of fibre 'cross section'. We focused on ventral tegmental area, locus coeruleus, and raphe nuclei as the main source of dopaminergic, noradrenergic, and serotoninergic fibres within the brainstem, respectively. Fourteen tracts of interest projecting from these brainstem nuclei were reconstructed using diffusion tractography, and compared by means of the product of fibre-density and cross-section (FDC). Finally, correlations of monoaminergic axonal damage with the modified fatigue impact scale scores were evaluated in MS. Fixel-based analysis revealed significant axonal damage - as measured by FDC reduction - within selective monoaminergic fibre-tracts projecting from brainstem nuclei in MS patients, in comparison to healthy controls; particularly within the dopaminergic-mesolimbic pathway, the noradrenergic-projections to prefrontal cortex, and serotoninergic-projections to cerebellum. Moreover, we observed significant correlations between severity of cognitive fatigue and axonal damage within the mesocorticolimbic tracts projecting from ventral tegmental area, as well as within the locus coeruleus projections to prefrontal cortex, suggesting a potential contribution of dopaminergic and noradrenergic pathways to central fatigue in MS. Our findings support the hypothesis that axonal damage along monoaminergic pathways contributes to the reduction/dysfunction of monoamines in MS and add new information on the mechanisms by which monoaminergic systems contribute to MS pathogenesis and fatigue. This supports the need for further research into monoamines as therapeutic targets aiming to combat and alleviate fatigue in MS.

Fatigue in irritable bowel syndrome is associated with plasma levels of TNF-α and mesocorticolimbic connectivity

Irritable bowel syndrome (IBS) is a symptom-based disorder of gut-brain interactions generating abdominal pain. It is also associated with a vulnerability to develop extraintestinal symptoms, with fatigue often reported as one of the most disturbing. Fatigue is related to brain function and inflammation in several disorders, however, the mechanisms of such relations in IBS remain elusive. This study aimed to elucidate fatigue and its association with a resting state network of mesocorticolimbic regions of known importance in fatigue, and to explore the possible role of circulating TNF-α levels in IBS and healthy controls (HC). Resting state functional magnetic resonance imaging (fMRI) was conducted in 88 IBS patients and 47 HC of similar age and gender to investigate functional connectivity between mesocorticolimbic regions. Further, fatigue impact on daily life and plasma levels of the proinflammatory cytokine tumor necrosis factor-α (TNF-α), of known relevance to immune activation in IBS, were also measured. The selected mesocorticolimbic regions indeed formed a functionally connected network in all participants. The nucleus accumbens (NAc), in particular, exhibited functional connectivity to all other regions of interest. In IBS, fatigue impact on daily life was negatively correlated with the connectivity between NAc and dorsolateral prefrontal cortex bilaterally (left p = 0.019; right p = 0.038, corrected for multiple comparisons), while in HC, fatigue impact on daily life was positively correlated to the connectivity between the right NAc and anterior middle insula in both hemispheres (left p = 0.009; right p = 0.011). We found significantly higher levels of TNF-α in IBS patients compared to HC (p = 0.001) as well as a positive correlation between TNF-α and fatigue impact on daily life in IBS patients (rho = 0.25, p = 0.02) but not in HC (rho = -0.13, p = 0.37). There was no association between functional connectivity in the mesocorticolimbic network and plasma levels of TNF-α in either group In summary, this novel multimodal study provides the first evidence that the vulnerability to fatigue in IBS is associated with connectivity within a mesocorticolimbic network as well as immune activation. These findings warrant further investigation, both peripherally and potentially with measurements of central immune activation as well.

Mind the gap: from neurons to networks to outcomes in multiple sclerosis

MRI studies have provided valuable insights into the structure and function of neural networks, particularly in health and in classical neurodegenerative conditions such as Alzheimer disease. However, such work is also highly relevant in other diseases of the CNS, including multiple sclerosis (MS). In this Review, we consider the effects of MS pathology on brain networks, as assessed using MRI, and how these changes to brain networks translate into clinical impairments. We also discuss how this knowledge can inform the targeting of MS treatments and the potential future directions for research in this area. Studying MS is challenging as its pathology involves neurodegenerative and focal inflammatory elements, both of which could disrupt neural networks. The disruption of white matter tracts in MS is reflected in changes in network efficiency, an increasingly random grey matter network topology, relative cortical disconnection, and both increases and decreases in connectivity centred around hubs such as the thalamus and the default mode network. The results of initial longitudinal studies suggest that these changes evolve rather than simply increase over time and are linked with clinical features. Studies have also identified a potential role for treatments that functionally modify neural networks as opposed to altering their structure.

Dynamic functional connectivity as a neural correlate of fatigue in multiple sclerosis

BACKGROUND

More than 80% of multiple sclerosis (MS) patients experience symptoms of fatigue. MS-related fatigue is only partly explained by structural (lesions and atrophy) and functional (brain activation and conventional static functional connectivity) brain properties.

OBJECTIVES

To investigate the relationship of dynamic functional connectivity (dFC) with fatigue in MS patients and to compare dFC with commonly used clinical and MRI parameters.

METHODS

In 35 relapsing-remitting MS patients (age: 42.83 years, female/male: 20/15, disease duration: 11 years) and 19 healthy controls (HCs) (age: 41.38 years, female/male: 11/8), fatigue was measured using the CIS-20r questionnaire at baseline and at 6-month follow-up. All subjects underwent structural and resting-state functional MRI at baseline. Global static functional connectivity (sFC) and dynamic functional connectivity (dFC) were calculated. dFC was assessed using a sliding-window approach by calculating the summed difference (diff) and coefficient of variation (cv) across windows. Moreover, regional connectivity between regions previously associated with fatigue in MS was estimated (i.e. basal ganglia and regions of the Default Mode Network (DMN): medial prefrontal, posterior cingulate and precuneal cortices). Hierarchical regression analyses were performed with forward selection to identify the most important correlates of fatigue at baseline. Results were not corrected for multiple testing due to the exploratory nature of the study.

RESULTS

Patients were more fatigued than HCs at baseline (p = 0.001) and follow-up (p = 0.002) and fatigue in patients was stable over time (p = 0.213). Patients had significantly higher baseline global dFC than HCs, but no difference in basal ganglia-DMN dFC. In the regression model for baseline fatigue in patients, basal ganglia-DMN dFC-cv (standardized β = -0.353) explained 12.5% additional variance on top of EDSS (p = 0.032). Post-hoc analysis revealed higher basal ganglia-DMN dFC-cv in non-fatigued patients compared to healthy controls (p = 0.013), whereas fatigued patients and healthy controls showed similar basal ganglia-DMN dFC.

CONCLUSIONS

Less dynamic connectivity between the basal ganglia and the cortex is associated with greater fatigue in MS patients, independent of disability status. Within patients, lower dynamics of these connections could relate to lower efficiency and increased fatigue. Increased dynamics in non-fatigued patients compared to healthy controls might represent a network organization that protects against fatigue or signal early network dysfunction.

Fatigue, depression, and pain in multiple sclerosis: How neuroinflammation translates into dysfunctional reward processing and anhedonic symptoms

Fatigue, depression, and pain affect the majority of multiple sclerosis (MS) patients, which causes a substantial burden to patients and society. The pathophysiology of these symptoms is not entirely clear, and current treatments are only partially effective. Clinically, these symptoms share signs of anhedonia, such as reduced motivation and a lack of positive affect. In the brain, they are associated with overlapping structural and functional alterations in areas involved in reward processing. Moreover, neuroinflammation has been shown to directly impede monoaminergic neurotransmission that plays a key role in reward processing. Here, we review recent neuroimaging and neuroimmunological findings, which indicate that dysfunctional reward processing might represent a shared functional mechanism fostering the symptom cluster of fatigue, depression, and pain in MS. We propose a framework that integrates these findings with a focus on monoaminergic neurotransmission and discuss its therapeutic implications, limitations, and perspectives.

Cognitive Fatigue Is Associated with Altered Functional Connectivity in Interoceptive and Reward Pathways in Multiple Sclerosis

Cognitive fatigue is common and debilitating among persons with multiple sclerosis (pwMS). Neural mechanisms underlying fatigue are not well understood, which results in lack of adequate treatment. The current study examined cognitive fatigue-related functional connectivity among 26 pwMS and 14 demographically matched healthy controls (HCs). Participants underwent functional magnetic resonance imaging (fMRI) scanning while performing a working memory task (n-back), with two conditions: one with higher cognitive load (2-back) to induce fatigue and one with lower cognitive load (0-back) as a control condition. Task-independent residual functional connectivity was assessed, with seeds in brain regions previously implicated in cognitive fatigue (dorsolateral prefrontal cortex (DLPFC), ventromedial prefrontal cortex (vmPFC), dorsal anterior cingulate cortex (dACC), insula, and striatum). Cognitive fatigue was measured using the Visual Analogue Scale of Fatigue (VAS-F). Results indicated that as VAS-F scores increased, HCs showed increased residual functional connectivity between the striatum and the vmPFC (crucial in reward processing) during the 2-back condition compared to the 0-back condition. In contrast, pwMS displayed increased residual functional connectivity from interoceptive hubs—the insula and the dACC—to the striatum. In conclusion, pwMS showed a hyperconnectivity within the interoceptive network and disconnection within the reward circuitry when experiencing cognitive fatigue.

Localised Grey Matter Atrophy in Multiple Sclerosis and Clinically Isolated Syndrome-A Coordinate-Based Meta-Analysis, Meta-Analysis of Networks, and Meta-Regression of Voxel-Based Morphometry Studies

Background: Atrophy of grey matter (GM) is observed in the earliest stages of multiple sclerosis (MS) and is associated with cognitive decline and physical disability. Localised GM atrophy in MS can be explored and better understood using magnetic resonance imaging and voxel-based morphometry (VBM). However, results are difficult to interpret due to methodological differences between studies. Methods: Coordinate-based analysis is a way to find the reliably observable results across multiple independent VBM studies. This work uses coordinate-based meta-analysis, meta-analysis of networks, and meta-regression to summarise the evidence from voxel-based morphometry of regional GM hanges in patients with MS and clinically isolated syndrome (CIS), and whether these measured changes are relatable to clinical features. Results: Thirty-four published articles reporting forty-four independent experiments using VBM for the assessment of GM atrophy between MS or CIS patients and healthy controls were identified. Analysis identified eight clusters of consistent cross-study reporting of localised GM atrophy involving both cortical and subcortical regions. Meta-network analysis identified a network-like pattern indicating that GM loss occurs with some symmetry between hemispheres. Meta-regression analysis indicates a relationship between disease duration or age and the magnitude of reported statistical effect in some deep GM structures. Conclusions: These results suggest consistency in MRI-detectible regional GM loss across multiple MS studies, and the estimated effect sizes and symmetries can help design prospective studies to test specific hypotheses.