Functional MRI in multiple sclerosis

Advanced neuroimaging techniques to explore the effects of motor and cognitive rehabilitation in multiple sclerosis

INTRODUCTION

Progress in magnetic resonance imaging (MRI) technology and analyses is improving our comprehension of multiple sclerosis (MS) pathophysiology. These advancements, which enable the evaluation of atrophy, microstructural tissue abnormalities, and functional plasticity, are broadening our insights into the effectiveness and working mechanisms of motor and cognitive rehabilitative treatments.

AREAS COVERED

This narrative review with selected studies discusses findings derived from the application of advanced MRI techniques to evaluate structural and functional neuroplasticity modifications underlying the effects of motor and cognitive rehabilitative treatments in people with MS (PwMS). Current applications as outcome measure in longitudinal trials and observational studies, their interpretation and possible pitfalls and limitations in their use are covered. Finally, we examine how the use of these techniques could evolve in the future to improve monitoring of motor and cognitive rehabilitative treatments.

EXPERT COMMENTARY

Despite substantial variability in study design and participant characteristics in rehabilitative studies for PwMS, improvements in motor and cognitive functions accompanied by structural and functional brain modifications induced by rehabilitation can be observed. However, significant enhancements to refine rehabilitation strategies are needed. Future studies in this field should strive to implement standardized methodologies regarding MRI acquisition and processing, possibly integrating multimodal measures. This will help identifying relevant markers of treatment response in PwMS, thus improving the use of rehabilitative interventions at individual level. The combination of motor and cognitive strategies, longer periods of treatment, as well as adequate follow-up assessments will contribute to enhance the quality of evidence in support of their routine use.

Resting-state functional MRI in multicenter studies on multiple sclerosis: a report on raw data quality and functional connectivity features from the Italian Neuroimaging Network Initiative

The Italian Neuroimaging Network Initiative (INNI) is an expanding repository of brain MRI data from multiple sclerosis (MS) patients recruited at four Italian MRI research sites. We describe the raw data quality of resting-state functional MRI (RS-fMRI) time-series in INNI and the inter-site variability in functional connectivity (FC) features after unified automated data preprocessing. MRI datasets from 489 MS patients and 246 healthy control (HC) subjects were retrieved from the INNI database. Raw data quality metrics included temporal signal-to-noise ratio (tSNR), spatial smoothness (FWHM), framewise displacement (FD), and differential variation in signals (DVARS). Automated preprocessing integrated white-matter lesion segmentation (SAMSEG) into a standard fMRI pipeline (fMRIPrep). FC features were calculated on pre-processed data and harmonized between sites (Combat) prior to assessing general MS-related alterations. Across centers (both groups), median tSNR and FWHM ranged from 47 to 84 and from 2.0 to 2.5, and median FD and DVARS ranged from 0.08 to 0.24 and from 1.06 to 1.22. After preprocessing, only global FC-related features were significantly correlated with FD or DVARS. Across large-scale networks, age/sex/FD-adjusted and harmonized FC features exhibited both inter-site and site-specific inter-group effects. Significant general reductions were obtained for somatomotor and limbic networks in MS patients (vs. HC). The implemented procedures provide technical information on raw data quality and outcome of fully automated preprocessing that might serve as reference in future RS-fMRI studies within INNI. The unified pipeline introduced little bias across sites and appears suitable for multisite FC analyses on harmonized network estimates.

Brain functional connectivity analysis in patients with relapsing-remitting multiple sclerosis: A graph theory approach of EEG resting state

Multiple sclerosis (MS) is an autoimmune disease related to the central nervous system (CNS). This study aims to investigate the effects of MS on the brain's functional connectivity network using the electroencephalogram (EEG) resting-state signals and graph theory approach. Resting-state eyes-closed EEG signals were recorded from 20 patients with relapsing-remitting MS (RRMS) and 18 healthy cases. In this study, the prime objective is to calculate the connectivity between EEG channels to assess the differences in brain functional network global features. The results demonstrated lower cortical activity in the alpha frequency bands and higher activity for the gamma frequency bands in patients with RRMS compared to the healthy group. In this study, graph metric calculations revealed a significant difference in the diameter of the functional brain network based on the directed transfer function (DTF) measure between the two groups, indicating a higher diameter in RRMS cases for the alpha frequency band. A higher diameter for the functional brain network in MS cases can result from anatomical damage. In addition, considerable differences between the networks' global efficiency and transitivity based on the imaginary part of the coherence (iCoh) measure were observed, indicating higher global efficiency and transitivity in the delta, theta, and beta frequency bands for RRMS cases, which can be related to the compensatory functional reaction from the brain. This study indicated that in RRMS cases, some of the global characteristics of the brain's functional network, such as diameter and global efficiency, change and can be illustrated even in the resting-state condition when the brain is not under cognitive load.

Multiple Sclerosis and Aging: The Dynamics of Demyelination and Remyelination

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) leading to demyelination and neurodegeneration. Life expectancy and age of onset in MS patients have been rising over the last decades, and previous studies have shown that age affects disease progression. Therefore, age appears as one of the most important factors in accumulating disability in MS patients. Indeed, the degeneration of oligodendrocytes (OGDs) and OGD precursors (OPCs) increases with age, in association with increased inflammatory activity of astrocytes and microglia. Similarly, age-related neuronal changes such as mitochondrial alterations, an increase in oxidative stress, and disrupted paranodal junctions can impact myelin integrity. Conversely, once myelination is complete, the long-term integrity of axons depends on OGD supply of energy. These alterations determine pathological myelin changes consisting of myelin outfolding, splitting, and accumulation of multilamellar fragments. Overall, these data demonstrate that old mature OGDs lose their ability to produce and maintain healthy myelin over time, to induce de novo myelination, and to remodel pre-existing myelinated axons that contribute to neural plasticity in the CNS. Furthermore, as observed in other tissues, aging induces a general decline in regenerative processes and, not surprisingly, progressively hinders remyelination in MS. In this context, this review will provide an overview of the current knowledge of age-related changes occurring in cells of the oligodendroglial lineage and how they impact myelin synthesis, axonal degeneration, and remyelination efficiency.

Diffusion basis spectrum imaging measures anti-inflammatory and neuroprotective effects of fingolimod on murine optic neuritis

OBJECTIVE

To prospectively determine whether diffusion basis spectrum imaging (DBSI) detects, differentiates and quantitates coexisting inflammation, demyelination, axonal injury and axon loss in mice with optic neuritis (ON) due to experimental autoimmune encephalomyelitis (EAE), and to determine if DBSI accurately measures effects of fingolimod on underlying pathology.

METHODS

EAE was induced in 7-week-old C57BL/6 female mice. Visual acuity (VA) was assessed daily to detect onset of ON after which daily oral-treatment with either fingolimod (1 mg/kg) or saline was given for ten weeks. In vivo DBSI scans of optic nerves were performed at baseline, 2-, 6- and 10-weeks post treatment. DBSI-derived metrics including restricted isotropic diffusion tensor fraction (putatively reflecting cellularity), non-restricted isotropic diffusion tensor fraction (putatively reflecting vasogenic edema), DBSI-derived axonal volume, axial diffusivity, λ_∥ (putatively reflecting axonal integrity), and increased radial diffusivity, λ_⊥ (putatively reflecting demyelination). Mice were killed immediately after the last DBSI scan for immunohistochemical assessment.

RESULTS

Optic nerves of fingolimod-treated mice exhibited significantly better (p < 0.05) VA than saline-treated group at each time point. During ten-week of treatment, DBSI-derived non-restricted and restricted-isotropic-diffusion-tensor fractions, and axonal volumes were not significantly different (p > 0.05) from the baseline values in fingolimod-treated mice. Transient DBSI-λ_∥ decrease and DBSI-λ_⊥ increase were detected during Fingolimod treatment. DBSI-derived metrics assessed in vivo significantly correlated (p < 0.05) with the corresponding histological markers.

CONCLUSION

DBSI was used to assess changes of the underlying optic nerve pathologies in EAE mice with ON, exhibiting great potential as a noninvasive outcome measure for monitoring disease progression and therapeutic efficacy for MS.

Management of Traumatic Trigeminal and Facial Nerve Injuries

In the area of craniomaxillofacial trauma, neurosensory disturbances are encountered commonly, especially with regard to the trigeminal and facial nerve systems. This article reviews the specific microanatomy of both cranial nerves V and VII, and evaluates contemporary neurosensory testing, current imaging modalities, and available nerve injury classification systems. In addition, the article proposes treatment paradigms for management of trigeminal and facial nerve injuries, specifically with regard to the craniomaxillofacial trauma setting.

Relationship between intensive care unit-acquired weakness, fatigability and fatigue: What role for the central nervous system?

PURPOSE

To provide a comprehensive review of studies that have investigated fatigue in intensive care unit (ICU) survivors and questions the potential link between intensive care unit-acquired weakness (ICUAW), fatigability and fatigue. We also question whether the central nervous system (CNS) may be the link between these entities.

MATERIAL AND METHODS

A narrative review of the literature that investigated fatigue in ICU survivors and review of clinical trials enabling understanding of CNS alterations in response to ICU stays.

RESULTS

Fatigue is a pervasive and debilitating symptom in ICU survivors that can interfere with rehabilitation. Due to the complex pathophysiology of fatigue, more work is required to understand the roles of ICUAW and/or fatigability in fatigue to provide a more holistic understanding of this symptom. While muscle alterations have been well documented in ICU survivors, we believe that CNS alterations developing early during the ICU stay may play a role in fatigue.

CONCLUSIONS

Fatigue should be considered and treated in ICU survivors. The causes of fatigue are likely to be specific to the individual. Understanding the role that ICUAW and fatigability may have in fatigue would allow to tailor individual treatment to prevent this persistent symptom and improve quality of life.

Morphological MRI phenotypes of multiple sclerosis differ in resting-state brain function

We aimed to assess differences in resting-state functional connectivity (FC) between distinct morphological MRI-phenotypes in multiple sclerosis (MS). Out of 180 MS patients, we identified those with high T2-hyperintense lesion load (T2-LL) and high normalized brain volume (NBV; a predominately white matter damage group, WMD; N = 37) and patients with low T2-LL and low NBV (N = 37; a predominately grey matter damage group; GMD). Independent component analysis of resting-state fMRI was used to test for differences in the sensorimotor network (SMN) between MS MRI-phenotypes and compared to 37 age-matched healthy controls (HC). The two MS groups did not differ regarding EDSS scores, disease duration and distribution of clinical phenotypes. WMD compared to GMD patients showed increased FC in all sub-units of the SMN (sex- and age-corrected). WMD patients had increased FC compared to HC and GMD patients in the central SMN (leg area). Only in the WMD group, higher EDSS scores and T2-LL correlated with decreased connectivity in SMN sub-units. MS patients with distinct morphological MRI-phenotypes also differ in brain function. The amount of focal white matter pathology but not global brain atrophy affects connectivity in the central SMN (leg area) of the SMN, consistent with the notion of a disconnection syndrome.

Brain activation patterns associated with paragraph learning in persons with multiple sclerosis: The MEMREHAB trial

The modified Story Memory Technique (mSMT) is a memory rehabilitation program that combines training in visualization and context formation to improve learning and memory. Previous studies have shown improvement in learning and memory in individuals with multiple sclerosis (MS) after undergoing the mSMT, including changes in brain activity related to working memory and word encoding. The current study examined changes in brain activity in 16 individuals diagnosed with MS (n _treatment = 6; n _{placebo control} = 10) when they were presented with to-be-remembered information within a meaningful context (i.e. a paragraph) from before to after mSMT treatment. We expected treatment-related changes in brain activation in the language network (LAN), default mode network (DMN), and executive control network (ECN). Consistent with this prediction, fMRI results revealed reduced brain activation in the LAN, DMN and ECN after completing the mSMT treatment in the context of paragraph learning. While no significant behavioral changes were observed, a marginally significant improvement with a large effect size was noted between baseline and follow-up performance on the Rivermead Behavioral Memory Test in persons who completed treatment. Results are discussed in terms of the impact of imagery training on patterns of cerebral activation when learning words presented within a context.

Considerations of power and sample size in rehabilitation research

With the current emphasis on power and reproducibility, pressures are rising to increase sample sizes in rehabilitation research in order to reflect more accurate effect estimation and generalizable results. The conventional way of increasing power by enrolling more participants is less feasible in some fields of research. In particular, rehabilitation research faces considerable challenges in achieving this goal. We describe the specific challenges to increasing power by recruiting large sample sizes and obtaining large effects in rehabilitation research. Specifically, we discuss how variability within clinical populations, lack of common standards for selecting appropriate control groups; potentially reduced reliability of measurements of brain function in individuals recovering from a brain injury; biases involved in a priori effect size estimation, and higher budgetary and staffing requirements can influence considerations of sample and effect size in rehabilitation. We also describe solutions to these challenges, such as increased sampling per participant, improving experimental control, appropriate analyses, transparent result reporting and using innovative ways of harnessing the inherent variability of clinical populations. These solutions can improve statistical power and produce reliable and valid results even in the face of limited availability of large samples.

MRI quality control for the Italian Neuroimaging Network Initiative: moving towards big data in multiple sclerosis

The Italian Neuroimaging Network Initiative (INNI) supports the creation of a repository, where MRI, clinical, and neuropsychological data from multiple sclerosis (MS) patients and healthy controls are collected from Italian Research Centers with internationally recognized expertise in MRI applied to MS. However, multicenter MRI data integration needs standardization and quality control (QC). This study aimed to implement quantitative measures for characterizing the standardization and quality of MRI collected within INNI. MRI scans of 423 MS patients, including 3D T₁- and T₂-weighted, were obtained from INNI repository (from Centers A, B, C, and D). QC measures were implemented to characterize: (1) head positioning relative to the magnet isocenter; (2) intensity inhomogeneity; (3) relative image contrast between brain tissues; and (4) image artefacts. Centers A and D showed the most accurate subject positioning within the MR scanner (median z-offsets = - 2.6 ± 1.7 cm and - 1.1 ± 2 cm). A low, but significantly different, intensity inhomogeneity on 3D T₁-weighted MRI was found between all centers (p < 0.05), except for Centers A and C that showed comparable image bias fields. Center D showed the highest relative contrast between gray and normal appearing white matter (NAWM) on 3D T₁-weighed MRI (0.63 ± 0.04), while Center B showed the highest relative contrast between NAWM and MS lesions on FLAIR (0.21 ± 0.06). Image artefacts were mainly due to brain movement (60%) and ghosting (35%). The implemented QC procedure ensured systematic data quality assessment within INNI, thus making available a huge amount of high-quality MRI to better investigate pathophysiological substrates and validate novel MRI biomarkers in MS.

Functional neuroplasticity in response to cerebello-thalamic injury underpins the clinical presentation of tremor in multiple sclerosis

BACKGROUND

Tremor is present in almost half of multiple sclerosis (MS) patients. The lack of understanding of its pathophysiology is hampering progress in development of treatments.

OBJECTIVES

To clarify the structural and functional brain changes associated with the clinical phenotype of upper limb tremor in people with MS.

METHODS

Fifteen healthy controls (46.1 ± 15.4 years), 27 MS participants without tremor (46.7 ± 11.6 years) and 42 with tremor (46.6 ± 11.5 years) were included. Tremor was quantified using the Bain score (0-10) for overall severity, handwriting and Archimedes spiral drawing. Functional magnetic resonance imaging activations were compared between participants groups during performance of a joystick task designed to isolate tremulous movement. Inflammation and atrophy of cerebello-thalamo-cortical brain structures were quantified.

RESULTS

Tremor participants were found to have atrophy of the cerebellum and thalamus, and higher ipsilateral cerebellar lesion load compared to participants without tremor (p < 0.020). We found higher ipsilateral activation in the inferior parietal lobule, the premotor cortex and supplementary motor area in MS tremor participants compared to MS participants without tremor during the joystick task. Finally, stronger activation in those areas was associated with lower tremor severity.

CONCLUSION

Subcortical neurodegeneration and inflammation along the cerebello-thalamo-cortical and cortical functional neuroplasticity contribute to the severity of tremor in MS.

Evaluation of MS related central fatigue using MR neuroimaging methods: Scoping review

BACKGROUND

Fatigue is a common and debilitating symptom in multiple sclerosis (MS). Over the past decade, a growing body of research has focussed on the pathophysiological mechanisms underlying central (cognitive and physical) fatigue in MS. The precise mechanisms causing fatigue in MS patients are complex and poorly understood, and may differ between patients. Advanced quantitative magnetic resonance imaging (MRI) techniques allow for objective assessment of disease pathology and have been used to characterise the pathophysiology of central fatigue in MS.

OBJECTIVE

To systematically review the existing literature of MRI-based studies assessing the pathophysiological mechanisms of MS-related central fatigue.

METHODS

A systematic literature search of four major databases (PubMed, Medline, Embase, Scopus and Google Scholar) was conducted to identify MRI-based studies of MS-related fatigue published in the past 20 years. Studies using the following MRI-based methods were included: structural (lesion load/atrophy), T1 relaxation time/magnetisation transfer ratio (MTR), diffusion tensor imaging (DTI), functional MRI (fMRI) and magnetic resonance spectroscopy (MRS).

RESULTS

A total of 92 studies were identified as meeting the search criteria and included for review. Structurally, regional gray/white matter atrophy, cortical thinning, decreased T1 relaxation times and reduced fractional anisotropy were associated with central fatigue in MS. Functionally, hyperactivity and reduced functional connectivity in several regional areas of frontal, parietal, occipital, temporal and cerebellum were suggested as causes of central fatigue. Biochemically, a reduction in N-acetyl aspartate/creatine and increased (glutamine+glutamate)/creatine ratios were correlated with fatigue severity in MS.

CONCLUSION

Several advanced quantitative MRI methods have been employed in the study of central fatigue in MS. Central fatigue in MS is associated with macro/microstructural and functional changes within specific brain regions (frontal, parietal, temporal and deep gray matter) and specific pathways/networks (cortico-cortical and cortico-subcortical). Alternations in the cortico-striatal-thalamocortical (CSTC) loop are correlated with the development of fatigue in MS patients.

Application of advanced MRI techniques to monitor pharmacologic and rehabilitative treatment in multiple sclerosis: current status and future perspectives

Introduction: Advances in magnetic resonance imaging (MRI) technology and analyses are improving our understanding of the pathophysiology of multiple sclerosis (MS). Due to their ability to grade the presence of irreversible tissue loss, microstructural tissue abnormalities, metabolic changes and functional plasticity, the application of these techniques is also expanding our knowledge on the efficacy and mechanisms of action of different pharmacological and rehabilitative treatments. Areas covered: This review discusses recent findings derived from the application of advanced MRI techniques to evaluate the structural and functional substrates underlying the effects of pharmacologic and rehabilitative treatments in patients with MS. Current applications as outcome in clinical trials and observational studies, their interpretation and possible pitfalls in their use are discussed. Finally, how these techniques could evolve in the future to improve monitoring of disease progression and treatment response is examined. Expert commentary: The number of treatments currently available for MS is increasing. The application of advanced MRI techniques is providing reliable and specific measures to better understand the targets of different treatments, including neuroprotection, tissue repair, and brain plasticity. This is a fundamental progress to move toward personalized medicine and individual treatment selection.

Classic Block Design "Pseudo"-Resting-State fMRI Changes After a Neurorehabilitation Program in Patients with Multiple Sclerosis

BACKGROUND AND PURPOSE

The goal of this study was to assess changes in the resting-state networks (RSNs) of patients with multiple sclerosis (MS) after a cognitive rehabilitation program (CRP), by retrospectively analyzing functional magnetic resonance imaging (fMRI) studies using the classical block design.

METHODS

Fifteen patients with MS (2 primary progressive, 3 relapsing-remitting, 10 secondary progressive) were scanned before and after the CRP on a 1.5T MRI scanner. In addition, patients underwent pre- and post-CRP neuropsychological assessment using a battery of standardized tests. Five healthy individuals were scanned at the same time points to confirm the test-retest reliability of the imaging technique. For each study, the individual fMRI blocks of rest were merged to produce a "pseudo"-resting-state (pseudo-RS) of 3 minutes duration. RS studies were analyzed with the MELODIC toolbox. A dual regression analysis was applied to estimate the longitudinal changes in RSNs of patients and test controls relative to a set of predefined RSNs used as templates.

RESULTS

In healthy individuals, there were no significant differences in RSN results between the two time points studied. In the group of patients with MS, significant differences were found post-CRP in the visual medial, cerebellar, auditory, and frontal-executive RSNs. Furthermore, synchronization increases in the frontal-executive RSN were associated with cognitive improvement on neuropsychological testing.

CONCLUSIONS

Results obtained using a pseudo-RS approach to analyze data from block-design fMRI studies suggest that a CRP of 5 weeks' duration induces measurable changes in specific RSNs of patients with MS.

Neuromuscular fatigue during exercise: Methodological considerations, etiology and potential role in chronic fatigue

The term fatigue is used to describe a distressing and persistent symptom of physical and/or mental tiredness in certain clinical populations, with distinct but ultimately complex, multifactorial and heterogenous pathophysiology. Chronic fatigue impacts on quality of life, reduces the capacity to perform activities of daily living, and is typically measured using subjective self-report tools. Fatigue also refers to an acute reduction in the ability to produce maximal force or power due to exercise. The classical measurement of exercise-induced fatigue involves neuromuscular assessments before and after a fatiguing task. The limitations and alternatives to this approach are reviewed in this paper in relation to the lower limb and whole-body exercise, given the functional relevance to locomotion, rehabilitation and activities of daily living. It is suggested that under some circumstances, alterations in the central and/or peripheral mechanisms of fatigue during exercise may be related to the sensations of chronic fatigue. As such, the neurophysiological correlates of exercise-induced fatigue are briefly examined in two clinical examples where chronic fatigue is common: cancer survivors and people with multiple sclerosis. This review highlights the relationship between objective measures of fatigability with whole-body exercise and perceptions of fatigue as a priority for future research, given the importance of exercise in relieving symptoms of chronic fatigue and/or overall disease management. As chronic fatigue is likely to be specific to the individual and unlikely to be due to a simple biological or psychosocial explanation, tailored exercise programmes are a potential target for therapeutic intervention.

Functional MRI in investigating cognitive impairment in multiple sclerosis

There is increasing evidence that the severity of the clinical manifestations of multiple sclerosis (MS) does not simply result from the extent of tissue destruction, but it rather represents a complex balance between tissue damage, tissue repair, and cortical reorganization. Functional magnetic resonance imaging (fMRI) provides information about the plasticity of the human brain. Therefore, it has the potential to provide important pieces of information about brain reorganization following MS-related structural damage. When investigating cognitive systems, fMRI changes have been described in virtually all patients with MS and different clinical phenotypes. These functional changes have been related to the extent of brain damage within and outside T2-visible lesions as well as to the involvement of specific central nervous system structures. It has also been suggested that a maladaptive recruitment of specific brain regions might be associated with the appearance of clinical symptoms in MS, such as fatigue and cognitive impairment. fMRI studies from clinically (and cognitively) impaired MS patients may be influenced by different task performances between patients and controls. As a consequence, new strategies have been introduced to assess the role, if any, of brain reorganization in severely impaired patients, including the analysis of resting-state networks. The enhancement of any beneficial effects of this brain adaptive plasticity should be considered as a potential target of therapy for MS.

Brain health: time matters in multiple sclerosis

INTRODUCTION

We present international consensus recommendations for improving diagnosis, management and treatment access in multiple sclerosis (MS). Our vision is that these will be used widely among those committed to creating a better future for people with MS and their families.

METHODS

Structured discussions and literature searches conducted in 2015 examined the personal and economic impact of MS, current practice in diagnosis, treatment and management, definitions of disease activity and barriers to accessing disease-modifying therapies (DMTs).

RESULTS

Delays often occur before a person with symptoms suggestive of MS sees a neurologist. Campaigns to raise awareness of MS are needed, as are initiatives to improve access to MS healthcare professionals and services. We recommend a clear treatment goal: to maximize neurological reserve, cognitive function and physical function by reducing disease activity. Treatment should start early, with DMT and lifestyle measures. All parameters that predict relapses and disability progression should be included in the definition of disease activity and monitored regularly when practical. On suboptimal control of disease activity, switching to a DMT with a different mechanism of action should be considered. A shared decision-making process that embodies dialogue and considers all appropriate DMTs should be implemented. Monitoring data should be recorded formally in registries to generate real-world evidence. In many jurisdictions, access to DMTs is limited. To improve treatment access the relevant bodies should consider all costs to all parties when conducting economic evaluations and encourage the continuing investigation, development and use of cost-effective therapeutic strategies and alternative financing models.

CONCLUSIONS

The consensus findings of an international author group recommend a therapeutic strategy based on proactive monitoring and shared decision-making in MS. Early diagnosis and improved treatment access are also key components.

Individual differences in depression are associated with abnormal function of the limbic system in multiple sclerosis patients

Background:

Depression is common in patients with multiple sclerosis (MS), although the brain mechanisms of this psychiatric condition in MS are poorly understood. Specifically, it remains to be determined whether depression in MS is related to altered activity and functional connectivity patterns within limbic circuits.

Methods:

Seventy-seven MS patients with variable levels of depression (as assessed via the Beck Depression Inventory) underwent functional magnetic resonance imaging while performing an emotional processing task. To conduct the functional connectivity analyses, the bilateral amygdala and hippocampus, two areas critically involved in the pathophysiology of depression, were chosen as ‘seed’ regions. Multiple regression models were used to assess how depression in MS patients was correlated with the activity and functional connectivity patterns within the limbic system.

Results:

Depression scores in MS patients were negatively correlated: (1) with the activity in the subgenual cingulate cortex; (2) with the functional connectivity between the hippocampus and orbitofrontal cortex as well as the dorsolateral prefrontal cortex, and (3) with the functional connectivity between the amygdala and dorsolateral prefrontal cortex.

Conclusions:

Our study showed that individual differences in depression in MS patients were significantly associated with altered regional activity and functional connectivity patterns within the limbic system.

Abnormalities of frontal-parietal resting-state functional connectivity are related to disease activity in patients with systemic lupus erythematosus

Cerebral involvement is common in patients with systemic Lupus erythematosus (SLE) and is characterized by multiple clinical presentations, including cognitive disorders, headaches, and syncope. Several neuroimaging studies have demonstrated cerebral dysfunction during different tasks among SLE patients; however, there have been few studies designed to characterize network alterations or to identify clinical markers capable of reflecting the cerebral involvement in SLE patients. This study was designed to characterize the profile of the cerebral activation area and the functional connectivity of cognitive function in SLE patients by using a task-based and a resting state functional magnetic resonance imaging (fMRI) technique, and to determine whether or not any clinical biomarkers could serve as an indicator of cerebral involvement in this disease. The well-established cognitive function test (Paced Visual Serial Adding Test [PVSAT]) was used. Thirty SLE patients without neuropsychiatric symptoms and 25 age- and gender-matched healthy controls were examined using PVSAT task-based and resting state fMRI. Outside the scanner, the performance of patients and the healthy controls was similar. In the PVSAT task-based fMRI, patients presented significantly expanded areas of activation, and the activated areas exhibited significantly higher functional connectivity strength in patients in the resting state. A positive correlation existed between individual connectivity strength and disease activity scoring. No correlation with cerebral involvement existed for serum markers, such as C3, C4, and anti-dsDNA. Thus, our findings may shed new light on the pathologic mechanism underlying neuropsychiatric SLE, and suggests that disease activity may be a potential effective biomarker reflecting cerebral involvement in SLE.

Evidence of impaired brain activity balance after passive sensorimotor stimulation in multiple sclerosis

OBJECTIVES

Examination of sensorimotor activation alone in multiple sclerosis (MS) patients may not yield a comprehensive view of cerebral response to task stimulation. Additional information may be obtained by examining the negative BOLD response (deactivation). Aim of this work was to characterize activation and deactivation patterns during passive hand movements in MS patients.

METHODS

13 relapsing remitting-MS patients (RRMS), 18 secondary progressive-MS patients (SPMS) and 15 healthy controls (HC) underwent an fMRI study during passive right-hand movements. Activation and deactivation contrasts in the three groups were entered into ANOVA, age and gender corrected. Post-hoc analysis was performed with one-sample and two-sample t-tests. For each patient we obtained lesion volume (LV) from both T1- and T2-weighted images.

RESULTS

Activations showed a progressive extension to the ipsilateral brain hemisphere according to the group and the clinical form (HC<RRMS<SPMS). Significant deactivation of the ipsilateral cortical sensorimotor areas was reduced in both patient groups with respect to HC. Deactivation of posterior cortical areas belonging to the default mode network (DMN), was increased in RRMS, but not in SPMS, with respect to HC. The amount of activation in the contralateral sensorimotor cortex was significantly correlated with that of deactivation in the DMN in HC and RRMS, but not in SPMS. Both increased activation and decreased deactivation patterns correlated with LV.

CONCLUSION

In RRMS patients, increased cortical activation was associated with increased deactivation of the posterior cortex suggesting a greater resting-state activity in the DMN, probably aimed at facilitating sensorimotor circuit engagement during task performance. In SPMS the coupling between increased sensorimotor activation/increased DMN deactivation was not observed suggesting disorganization between anticorrelated functional networks as a consequence of a higher level of disconnection.

Disease-specific molecular events in cortical multiple sclerosis lesions

Cortical lesions constitute an important part of multiple sclerosis pathology. Although inflammation appears to play a role in their formation, the mechanisms leading to demyelination and neurodegeneration are poorly understood. We aimed to identify some of these mechanisms by combining gene expression studies with neuropathological analysis. In our study, we showed that the combination of inflammation, plaque-like primary demyelination and neurodegeneration in the cortex is specific for multiple sclerosis and is not seen in other chronic inflammatory diseases mediated by CD8-positive T cells (Rasmussen's encephalitis), B cells (B cell lymphoma) or complex chronic inflammation (tuberculous meningitis, luetic meningitis or chronic purulent meningitis). In addition, we performed genome-wide microarray analysis comparing micro-dissected active cortical multiple sclerosis lesions with those of tuberculous meningitis (inflammatory control), Alzheimer's disease (neurodegenerative control) and with cortices of age-matched controls. More than 80% of the identified multiple sclerosis-specific genes were related to T cell-mediated inflammation, microglia activation, oxidative injury, DNA damage and repair, remyelination and regenerative processes. Finally, we confirmed by immunohistochemistry that oxidative damage in cortical multiple sclerosis lesions is associated with oligodendrocyte and neuronal injury, the latter also affecting axons and dendrites. Our study provides new insights into the complex mechanisms of neurodegeneration and regeneration in the cortex of patients with multiple sclerosis.

A qualitative review of the neurophysiological underpinnings of fatigue in multiple sclerosis

Fatigue is debilitating in multiple sclerosis (MS) and may have multiple causes. Recent investigations into objectively measurable correlates of fatigue have used transcranial magnetic stimulation (TMS) to examine a range of neurophysiological measures of neural excitability that may be altered in patients with MS. This qualitative review was conducted to test the hypothesis that changes in neural excitability are a contributing factor in MS-related fatigue. A search of the English language literature led to the compilation and synthesis of original research papers in which various aspects of neural excitability and neural transmission were measured using TMS in patients with MS. The resulting papers were classified into three categories of study relevant to fatigue: abnormalities in excitability and their correlation with self-reported fatigue; effects of exercise-induced fatigue on neural excitability; and effects of fatigue medications on neural excitability. Evidence of an association between fatigue and intracortical inhibition is both limited and conflicting, and no evidence suggests associations of fatigue with corticomotor excitability or neuronal conduction. Pharmacologically-induced changes in fatigue were found to correlate with changes in intracortical excitability. No conclusions could be drawn regarding neural excitability and exercise-induced fatigue, due to variability in study populations, outcome measures, and exercise protocols across different studies. Suggestions for future studies in this area are proposed with a view to identifying potentially modifiable factors contributing to fatigue in MS.

Analysis of "task-positive" and "task-negative" functional networks during the performance of the Symbol Digit Modalities Test in patients at presentation with clinically isolated syndrome suggestive of multiple sclerosis

An abnormal pattern of brain activations has been shown in patients with multiple sclerosis during the performance of several cognitive tasks. The aim of this study is to investigate abnormalities of the patterns of activation/deactivation in the functional networks related to "task-positive" and "task-negative" events during the execution of the Symbol Digit Modalities Test (SDMT) in patients with clinically isolated syndromes (CIS) and preserved cognitive abilities. Eighteen CIS patients within 3 months from their first clinical attack and 15 healthy controls (HC) underwent neuropsychological assessment and performed an adapted functional magnetic resonance imaging (fMRI) version of the SDMT. "Task-positive" responses to task execution and "task-negative" activity of the default mode network were compared between groups. A regression analysis was performed to investigate the correlation between fMRI results and T2 lesion load (T2 LL) and brain atrophy. Neuropsychological performance did not differ between groups. Compared to HC, CIS patients exhibited an enhanced deactivation of the "task-negative" network at the level of the posterior cingulate cortex, whereas no differences between groups were found when the patterns of "task-positive" events were compared. A regression analysis detected a correlation (p < 0.001,r ranging from 0.62 to 0.73) between T2 LL and "task-positive" activations of areas that are part of the attention network, comprising the anterior cingulate gyrus, left prefrontal gyrus and inferior parietal lobe. No correlation was found between patterns of functional modifications and brain atrophy. CIS patients experience an enhanced pattern of brain deactivations during cognitive performances, which might contribute to their normal neuropsychological status.

Altered functional MR imaging language activation in elderly individuals with cerebral leukoaraiosis

PURPOSE

To test the hypothesis that leukoaraiosis alters functional activation during a semantic decision language task.

MATERIALS AND METHODS

With institutional review board approval and written informed consent, 18 right-handed, cognitively healthy elderly participants with an aggregate leukoaraiosis lesion volume of more than 25 cm(3) and 18 age-matched control participants with less than 5 cm(3) of leukoaraiosis underwent functional MR imaging to allow comparison of activation during semantic decisions with that during visual perceptual decisions. Brain statistical maps were derived from the general linear model. Spatially normalized group t maps were created from individual contrast images. A cluster extent threshold of 215 voxels was used to correct for multiple comparisons. Intergroup random effects analysis was performed. Language laterality indexes were calculated for each participant.

RESULTS

In control participants, semantic decisions activated the bilateral visual cortex, left posteroinferior temporal lobe, left posterior cingulate gyrus, left frontal lobe expressive language regions, and left basal ganglia. Visual perceptual decisions activated the right parietal and posterior temporal lobes. Participants with leukoaraiosis showed reduced activation in all regions associated with semantic decisions; however, activation associated with visual perceptual decisions increased in extent. Intergroup analysis showed significant activation decreases in the left anterior occipital lobe (P=.016), right posterior temporal lobe (P=.048), and right basal ganglia (P=.009) in particpants with leukoariosis. Individual participant laterality indexes showed a strong trend (P=.059) toward greater left lateralization in the leukoaraiosis group.

CONCLUSION

Moderate leukoaraiosis is associated with atypical functional activation during semantic decision tasks. Consequently, leukoaraiosis is an important confounding variable in functional MR imaging studies of elderly individuals.

Classifying minimally disabled multiple sclerosis patients from resting state functional connectivity

Multiple sclerosis (MS), a variable and diffuse disease affecting white and gray matter, is known to cause functional connectivity anomalies in patients. However, related studies published to-date are post hoc; our hypothesis was that such alterations could discriminate between patients and healthy controls in a predictive setting, laying the groundwork for imaging-based prognosis. Using functional magnetic resonance imaging resting state data of 22 minimally disabled MS patients and 14 controls, we developed a predictive model of connectivity alterations in MS: a whole-brain connectivity matrix was built for each subject from the slow oscillations (<0.11 Hz) of region-averaged time series, and a pattern recognition technique was used to learn a discriminant function indicating which particular functional connections are most affected by disease. Classification performance using strict cross-validation yielded a sensitivity of 82% (above chance at p<0.005) and specificity of 86% (p<0.01) to distinguish between MS patients and controls. The most discriminative connectivity changes were found in subcortical and temporal regions, and contralateral connections were more discriminative than ipsilateral connections. The pattern of decreased discriminative connections can be summarized post hoc in an index that correlates positively (ρ=0.61) with white matter lesion load, possibly indicating functional reorganisation to cope with increasing lesion load. These results are consistent with a subtle but widespread impact of lesions in white matter and in gray matter structures serving as high-level integrative hubs. These findings suggest that predictive models of resting state fMRI can reveal specific anomalies due to MS with high sensitivity and specificity, potentially leading to new non-invasive markers.

Inflammation high-field magnetic resonance imaging

Multiple sclerosis (MS) is the most common inflammatory demyelinating disorder of the central nervous system (CNS). MS has been subject to high-field magnetic resonance (MR) imaging research to a great extent during the past years, and much data has been collected that might be helpful in the investigation of other inflammatory CNS disorders. This article reviews the value of high-field MR imaging in examining inflammatory MS abnormalities. Furthermore, possibilities and challenges for the future of high-field MR imaging in MS are discussed.

Brain MRI lesion load at 1.5T and 3T versus clinical status in multiple sclerosis

BACKGROUND/PURPOSE

To assess correlation between brain lesions and clinical status with 1.5T and 3T magnetic resonance imaging (MRI).

METHODS

Brain MRI fluid-attenuated inversion-recovery (FLAIR) sequences were performed in 32 multiple sclerosis (MS) patients. Expanded Disability Status Scale (EDSS) score (mean±standard deviation) was 2±2.0 (range 0-8), disease duration 9.3±8.0 (range .8-29) years.

RESULTS

FLAIR lesion volume (FLLV) at 3T was higher than at 1.5T (P=.01). Correlation between 1.5T FLLV and EDSS score was poor, while 3T FLLV correlated moderately and significantly (rs=.39, P=.03). When controlling for age and depression, correlations between FLLV and cognitive measures were significant at 1.5T for the Judgment of Line Orientation test (JLO) (rs=-.44, P=.05), the Symbol Digit Modalities Test (SDMT) (rs=-.49, P=.02), and the California Verbal Learning Test Delayed Free Recall (CVLT DR) (rs=-.44, P=.04). Correlations at 3T were also significant for these tests, but of greater magnitude: JLO (rs=-.70, P=.0005), SDMT (rs=-.73, P=.0001), CVLT DR (rs=-.061, P=.003). Additional significant correlations obtained only at 3T included the 2 second-paced auditory serial addition test (rs=-.55, P=.01), the Brief Visuospatial Memory Test-Delayed Free Recall (rs=-.56, P=.007), and the California Verbal Learning Test Total Recall (rs=-.42, P=.05).

CONCLUSION

MRI at 3T may boost sensitivity and improve validity in MS brain lesion assessment.

Advanced MRI in multiple sclerosis: current status and future challenges

MRI has rapidly become a leading research tool in the study of multiple sclerosis (MS). Conventional imaging is useful in diagnosis and management of the inflammatory stages of MS but has limitations in describing the degree of tissue injury and cause of progressive disability seen in later stages. Advanced MRI techniques hold promise for filling this void. These imaging tools hold great promise to increase understanding of MS pathogenesis and provide greater insight into the efficacy of new MS therapies.

Immunopathogenesis of multiple sclerosis

Multiple sclerosis (MS) is a suspected autoimmune disease in which myelin-specific CD4+ and CD8+ T cells enter the central nervous system (CNS) and initiate an inflammatory response directed against myelin and other components of the CNS. Acute MS exacerbations are believed be the result of active inflammation, and progression of disability is generally believed to reflect accumulation of damage to the CNS, particularly axonal damage. Over the last several years, the pathophysiology of MS is being appreciated to be much more complex, and it appears that the development of the MS plaque involves a large number of cell populations, including CD8+ T lymphocytes, B cells, and Th17 cells (a population of helper T cells that secrete the inflammatory cytokine IL-17). The axonal transection and degeneration that is thought to represent the basis for progressive MS is now recognized to begin early in the disease process and to continue in the progressive forms of the disease. Molecules important for limiting aberrant neural connections in the CNS have been identified, which suppress axonal sprouting and regeneration of transected axons within the CNS. Pathways have also been identified that prevent remyelination of the MS lesion by oligodendrocyte precursors. Novel neuroimaging methodologies and potential biomarkers are being developed to monitor various aspects of the disease process in MS. As we identify the pathways responsible for the clinical phenomena of MS, we will be able to develop new therapeutic strategies for this disabling illness of young adults.

Impaired cortical deactivation during hand movement in the relapsing phase of multiple sclerosis: a cross-sectional and longitudinal fMRI study

BACKGROUND

Little is known about the cortical activation changes during clinical relapses in multiple sclerosis (MS).

OBJECTIVE

To assess cross-sectional and longitudinal differences in functional magnetic resonance imaging (fMRI) cortical patterns between the relapsing and stable phases of MS.

METHODS

We studied 32 patients with relapsing-remitting MS with mild disability: 19 within 48 h of symptom onset of a new relapse (G1) and 13 in the stable phase, relapse-free for at least 6 months (G2). All patients underwent fMRI twice, upon entry (time 1) and 30-50 days later (time 2), during right-hand movement.

RESULTS

No between-group differences were observed in age, disability or T2 lesion load. Between-group analysis showed a significant difference in the ipsilateral precentral gyrus (IPG) activation at time 1. Activity differences in the IPG expressed reduced deactivation in G1 compared with G2. Longitudinal changes in brain activity in the IPG were significantly greater in G1 than G2. G1 patients with a slow clinical recovery (n = 8) showed different activity at baseline and greater activity changes over time in the IPG than patients with a fast recovery (n = 11).

CONCLUSION

This study shows that the relapsing phase is associated with reduced brain deactivation in the IPG, which is more marked in patients with a slow clinical recovery. Increased cortical excitability associated with inflammation may determine functional modifications within the ipsilateral motor area.

Voxelwise assessment of the regional distribution of damage in the brains of patients with multiple sclerosis and fatigue

BACKGROUND AND PURPOSE

Fatigue affects up to 90% of patients with MS. We assessed the regional distribution of lesions and atrophy of the normal-appearing WM and GM in patients with RRMS with fatigue compared with HC and patients with similar characteristics, but without fatigue.

MATERIALS AND METHODS

From 14 patients with RRMS without fatigue, 10 with RRMS with fatigue, and 14 HC, we acquired brain dual-echo and high-resolution T1-weighted scans. Voxel-wise distributions of GM, WM damage, and T2 lesions were compared between patients with fatigued and nonfatigued MS by using SPM5 software. We report results at P < .05, FWE corrected.

RESULTS

T2 lesion distribution and regional WM atrophy did not differ between patients with fatigued and nonfatigued MS. Compared with HC, patients with MS had significant WM atrophy in the posterior part of the corpus callosum and significant GM atrophy of the left superior frontal sulcus, left precentral gyrus, posterior cingulate cortex, right thalamus, and left middle frontal gyrus. No additional areas of atrophy were found in patients with nonfatigued MS compared with HC, whereas patients with fatigued MS also had atrophy of the left central sulcus. Atrophy in the left central sulcus and the precentral gyrus was more severe in patients with fatigued versus nonfatigued MS. In patients with MS, significant correlations were found between fatigue severity and GM atrophy in the left precentral gyrus (r = -0.73, P < .0001 uncorrected).

CONCLUSIONS

Atrophy of the primary sensorimotor area is likely to contribute to MS-related fatigue.

A multicentre study of motor functional connectivity changes in patients with multiple sclerosis

In this multicentre study involving eight European centres, we characterized the spatial pattern of functional connectivity (FC) in the sensorimotor network from 61 right-handed patients with multiple sclerosis (MS) and 74 age-matched healthy subjects assessed with the use of functional magnetic resonance imaging (fMRI) and a simple motor task of their right dominant hand. FC was investigated by using: (i) voxel-wise correlations between the left sensorimotor cortex (SMC) and any other area in the brain; and (ii) bivariate correlations between time series extracted from several regions of interest (ROIs) belonging to the sensorimotor network. Both healthy controls and MS patients had significant FC between the left SMC and several areas of the sensorimotor network, including the bilateral postcentral and precentral gyri, supplementary motor area, middle frontal gyri, insulae, secondary somatosensory cortices, thalami, and right cerebellum. Voxel-wise assessment of FC revealed increased connectivity between the left SMC and the right precentral gyrus, right middle frontal gyrus (MFG) and bilateral postcentral gyri in MS patients as compared with controls. ROI analysis also showed a widespread pattern of altered connectivity, characterized by increased FC between the right MFG, the left insula and the right inferior frontal gyrus in comparison with many regions of the sensorimotor network. These results provide further evidence for increased bihemispheric contributions to motor control in patients with MS relative to healthy controls. They further suggest that multicentre fMRI studies of FC changes are possible, and provide a potential imaging biomarker for use in experimental therapeutic studies directed at enhancing adaptive plasticity in the disease.

Functional brain network changes associated with maintenance of cognitive function in multiple sclerosis

In multiple sclerosis (MS) functional changes in connectivity due to cortical reorganization could lead to cognitive impairment (CI), or reflect a re-adjustment to reduce the clinical effects of widespread tissue damage. Such alterations in connectivity could result in changes in neural activation as assayed by executive function tasks. We examined cognitive function in MS patients with mild to moderate CI and age-matched controls. We evaluated brain activity using functional magnetic resonance imaging (fMRI) during the successful performance of the Wisconsin card sorting (WCS) task by MS patients, showing compensatory maintenance of normal function, as measured by response latency and error rate. To assess changes in functional connectivity throughout the brain, we performed a global functional brain network analysis by computing voxel-by-voxel correlations on the fMRI time series data and carrying out a hierarchical cluster analysis. We found that during the WCS task there is a significant reduction in the number of smaller size brain functional networks, and a change in the brain areas representing the nodes of these networks in MS patients compared to age-matched controls. There is also a concomitant increase in the strength of functional connections between brain loci separated at intermediate-scale distances in these patients. These functional alterations might reflect compensatory neuroplastic reorganization underlying maintenance of relatively normal cognitive function in the face of white matter lesions and cortical atrophy produced by MS.

Mechanisms of neuronal dysfunction and degeneration in multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system. Due to its high prevalence, MS is the leading cause of non-traumatic neurological disability in young adults in the United States and Europe. The clinical disease course is variable and starts with reversible episodes of neurological disability in the third or fourth decade of life. This transforms into a disease of continuous and irreversible neurological decline by the sixth or seventh decade. Available therapies for MS patients have little benefit for patients who enter this irreversible phase of the disease. It is well established that irreversible loss of axons and neurons are the major cause of the irreversible and progressive neurological decline that most MS patients endure. This review discusses the etiology, mechanisms and progress made in determining the cause of axonal and neuronal loss in MS.

Functional MR imaging correlates of neuropsychological impairment in primary-progressive multiple sclerosis

BACKGROUND AND PURPOSE

Cognitive deficits affect

MATERIALS AND METHODS

From 16 right-handed patients with PPMS and 17 matched controls, structural and fMRIs (during the performance of the 2-back task) were acquired. Neuropsychological tests exploring memory, attention, and frontal lobe cognitive domains were administered. T2 LL, NBV, and CC areas were measured.

RESULTS

Six patients with PPMS were CI. Structural MR imaging measures did not differ between patients who were CI and those who were CP. Compared with patients who were CI, patients who were CP had increased activations of the left caudate nucleus, PFC, and inferior parietal lobule. Compared with controls and patients who were CP, patients who were CI had increased activations of the SII, cerebellum, and insula. Compared with controls, they also had increased activations of the right precentral gyrus and a reduced recruitment of the left PFC. In patients with PPMS, a decreased composite cognitive score correlated with increased activity of the cerebellum, insula, and SII, as well as decreased PFC activity. T2 LL correlated with decreased PFC recruitment and increased SII recruitment.

CONCLUSIONS

In PPMS, an increased recruitment of cognitive-related networks might represent a functional reserve with the potential to limit the severity of cognitive impairment. The accumulation of T2 lesions and the consequent exhaustion of frontal lobe plasticity might contribute to cognitive impairment in PPMS.

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Key Words Collapse

MESH Headings

• Adult
• Aged
• Brain/physiopathology
• Cerebellum/physiopathology
• Cognition Disorders/diagnosis
• Cognition Disorders/etiology
• Cognition Disorders/physiopathology
• Female
• Frontal Lobe/physiopathology
• Humans
• Magnetic Resonance Imaging
• Male
• Middle Aged
• Multiple Sclerosis, Chronic Progressive/complications
• Multiple Sclerosis, Chronic Progressive/diagnosis
• Multiple Sclerosis, Chronic Progressive/physiopathology
• Neuronal Plasticity/physiology
• Neuropsychological Tests
• Parietal Lobe/physiopathology
• Severity of Illness Index

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Grants Collapse

Affiliation(s)

M A Rocca Neuroimaging Research Unit, Institute of Experimental Neurology, Scientific Institute and University Ospedale San Raffaele, Milan, Italy
G Riccitelli
M Rodegher
A Ceccarelli
A Falini
M Falautano
A Meani
G Comi
Massimo Filippi

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Cortical functional reorganization and its relationship with brain structural damage in patients with benign multiple sclerosis

Background: Patients with multiple sclerosis (MS) who have a favourable clinical status several years after disease onset are classified as ‘benign’. In many cases brain tissue damage does not differ between benign MS and the ‘classical’ MS forms.

Objective: To assess whether the favourable clinical course in benign MS could be explained by the presence of an efficient functional cortical reorganization.

Method: Twenty-five right-handed patients with benign MS (defined as having Expanded Disability Status Scale ≤ 3 and disease duration >15 years) underwent functional MRI during a simple motor task (right-hand tapping) to assess movement-associated brain activation. This was compared with that of 10 patients with relapsing—remitting MS and 10 normal controls. Benign MS patients also underwent conventional brain MRI and magnetization transfer imaging, which was compared with an identical examination obtained 1 year before. Quantitative structural magnetic resonance measures were baseline and changes over time in T2-lesion volume, magnetization transfer ratio in T2 lesions and normal-appearing brain and total brain volume.

Results: Movement-related activation was greater in patients with benign MS than in those with relapsing—remitting MS or normal controls, extensively involving bilateral regions of the sensorimotor network as well as basal ganglia, insula and cerebellum. Greater activation correlated with lower T2-lesion magnetization transfer ratio, and with decreasing brain volume and increasing T2 lesion volume.

Conclusions: The results suggest that bilateral brain networks, beyond those normally engaged in motor tasks, are recruited during a simple hand movement in patients with benign MS. This increased activation is probably the expression of an extensive, compensatory and tissue-damage related functional cortical reorganization. This can explain, at least in part, the favourable clinical expression of patients with benign MS.

Advanced magnetic resonance imaging techniques to better understand multiple sclerosis

Magnetic resonance imaging (MRI) has considerably improved the diagnosis and monitoring of multiple sclerosis (MS). Conventional MRI such as T₂-weighted and gadolinium-enhanced T₁-weighted sequences detect focal lesions of the white matter, damage of the blood-brain barrier, and tissue loss and inflammatory activity within lesions. However, these conventional MRI metrics lack the specificity required for characterizing the underlying pathophysiology, especially diffuse damage occurring throughout the whole central nervous system. To overcome these limitations, advanced MRI techniques have been developed to get more sensitive and specific parameters of focal and diffuse brain damage. Among these techniques, magnetization transfer imaging, diffusion MRI, functional MRI, and magnetic resonance spectroscopy are the most significant. In this article, we provide an overview of these advanced MRI techniques and their contribution to the better characterization and understanding of MS.

Is a preserved functional reserve a mechanism limiting clinical impairment in pediatric MS patients?

We evaluated the functional magnetic resonance imaging (fMRI) correlates of simple movement performance in patients with pediatric multiple sclerosis (MS) and their relation with the extent of T2 lesion volume (LV), to improve our understanding of the mechanisms leading to their short/medium term favorable clinical course. We obtained fMRI during repetitive flexion-extension of the last four fingers of the right hand and brain dual-echo scans from 17 right-handed patients with pediatric relapsing-remitting MS and 9 sex- and age-matched right-handed healthy controls. T2 LV was measured using a local thresholding segmentation technique. fMRI activations and functional connectivity analysis were performed using SPM2. Compared to controls, pediatric MS patients had an increased recruitment of the left (L) primary sensorimotor cortex (SMC). They also showed reduced functional connectivity between the L primary SMC and the L thalamus (P = 0.03), the L insula and the L secondary sensorimotor cortex (SII) (P = 0.02), the supplementary motor area and the L SII (P = 0.02), the L thalamus and the L insula (P = 0.01) and the L thalamus and the L SII (P = 0.003). In patients with pediatric MS, the activity of the L primary SMC was significantly correlated with brain T2 LV (r = 0.78). No correlation was found between coefficients of abnormal connectivity and structural MRI measures. The maintenance of a selective and strictly lateralized pattern of movement-associated brain activations and a modulation of its functional connections suggest a preserved functional reserve in patients with pediatric MS, which, in turn, might contribute to explain their favorable clinical evolution at short/medium term.

Abnormal connectivity of the sensorimotor network in patients with MS: a multicenter fMRI study

In this multicenter study, we used dynamic causal modeling to characterize the abnormalities of effective connectivity of the sensorimotor network in 61 patients with multiple sclerosis (MS) compared with 74 age-matched healthy subjects. We also investigated the correlation of such abnormalities with findings derived from structural MRI. In a subgroup of subjects, diffusion tensor (DT) MRI metrics of the corpus callosum and the left corticospinal tract (CST) were also assessed. MS patients showed increased effective connectivity relative to controls between: (a) the left primary SMC and the left dorsal premotor cortex (PMd), (b) the left PMd and the supplementary motor areas (SMA), (c) the left secondary sensorimotor cortex (SII) and the SMA, (d) the right SII and the SMA, (e) the left SII and the right SII, and (f) the right SMC and the SMA. MS patients had relatively reduced effective connectivity between the left SMC and the right cerebellum. No interaction was found between disease group and center. Coefficients of altered connectivity were weakly correlated with brain T2 LV, but moderately correlated with DT MRI-measured damage of the left CST. In conclusion, large multicenter fMRI studies of effective connectivity changes in diseased people are feasible and can facilitate studies with sample size large enough for robust outcomes. Increased effective connectivity in the patients for the simple motor task suggests local network modulation contributing to enhanced long-distance effective connectivity in MS patients. This extends and generalizes previous evidence that enhancement of effective connectivity may provide an important compensatory mechanism in MS.

Ipsilateral cortical fMRI responses after peripheral nerve damage in rats reflect increased interneuron activity

In the weeks following unilateral peripheral nerve injury, the deprived primary somatosensory cortex (SI) responds to stimulation of the ipsilateral intact limb as demonstrated by functional magnetic resonance imaging (fMRI) responses. The neuronal basis of these responses was studied by using high-resolution fMRI, in vivo electrophysiological recordings, and juxtacellular neuronal labeling in rats that underwent an excision of the forepaw radial, median, and ulnar nerves. These nerves were exposed but not severed in control rats. Significant bilateral increases of fMRI responses in SI were observed in denervated rats. In the healthy SI of the denervated rats, increases in fMRI responses were concordant with increases in local field potential (LFP) amplitude and an increased incidence of single units responding compared with control rats. In contrast, in the deprived SI, increases in fMRI responses were associated with a minimal change in LFP amplitude but with increased incidence of single units responding. Based on action potential duration, juxtacellular labeling, and immunostaining results, neurons responding to intact forepaw stimulation in the deprived cortex were identified as interneurons. These results suggest that the increases in fMRI responses in the deprived cortex reflect increased interneuron activity.

Tipping the balance: anti-tumour necrosis factor alpha therapy may damage cerebral nerve reservation

Anti-tumour necrosis factor alpha therapy has transformed the treatment of certain inflammatory diseases including rheumatoid arthritis, inflammatory bowel disease and ankylosing spondylitis, but onset of demyelinating events associated with multiple sclerosis as an adverse event was continuously reported, and such adverse events were only viewed as occasional. Multiple sclerosis is an autoimmune demyelinating disorder affecting central nervous system, with varied clinical manifestations of cognitive, visual and motor network disorder. Recently, there is increasing evidence from functional magnetic resonance that cortical reorganization, a property that allows the central nervous system to adapt itself to various brain insults, which was viewed as to limit the clinical expression of tissue damage in patients with multiple sclerosis. In light of the mentioned above, we hypothesis that cerebral tissue damage may existed in a broader aspects of patients treated with anti-tumour necrosis factor therapy, but its clinical manifestations from brain lesions were compensated by cortical reorganization. In other words, cerebral nerve reservation may be damaged by the therapy. If confirmed, the hypothesis may lead to a safety concern of the therapy, and an insight of the pathophysiology of both multiple sclerosis and certain inflammatory diseases.

The future of multiple sclerosis treatment

Recent years have seen considerable evolution and increasing sophistication of our concepts of the pathophysiology of multiple sclerosis. These new notions include the increased recognition of the importance of extralesional pathology, of the interplay between inflammation and neurodegenerative changes, pathophysiological heterogeneity and additional immune cell populations contributing to disease. These advances have driven the development and evaluation of new therapeutic strategies and outcome measures for clinical trials. A sizeable number of new immunomodulatory and immunosuppressive agents are under development and attracting great attention. These may offer potential advantages over existing treatments in terms of convenience and efficacy, but certain agents may raise safety concerns. In addition, neuroprotective and repair strategies are beginning to be considered. Not all of these agents will eventually be marketed but they will all help us gain insight into the pathophysiology of multiple sclerosis and decipher the mechanisms that underlie its heterogeneity. The place that these therapies will come to occupy in future years will depend on their relative benefits and risks.