C. Wegner

Neocortical neuronal, synaptic, and glial loss in multiple sclerosis

Background: Recent pathologic investigations have shown that neocortical lesions are frequent in multiple sclerosis (MS). Structural MRI has shown that neocortical atrophy occurs early and can be substantial, but the specific substrate for this atrophy has not been defined quantitatively. Objective: To investigate cortical thickness as well as neuronal, glial, and synaptic densities in MS. Methods: We studied brain samples from 22 patients with MS and 17 control subjects. Neocortical lesions and cortical thickness were assessed on sections stained for myelin basic protein. Neuronal, glial, and synaptic densities were measured in type I leukocortical lesions, nonlesional neocortex, and non-MS control cortex. Immunoautoradiography was used to quantify synaptic densities. Results: Neocortical lesions were common in patients with MS. Subpial type III (44%) and leukocortical type I (38%) lesions were more abundant than intracortical type II (18%) lesions. An overall relative neocortical thinning of 10% (p = 0.016) was estimated for the patients. Within the type I lesions, we found evidence for substantial cell (glial, 36%, p = 0.001; neuronal, 10%, p = 0.032) and synaptic (47% decrease in synaptophysin, p = 0.001) loss. Nonlesional neocortex did not show significant relative changes in neuronal, glial, or synaptic density. Conclusions: Neocortical neuronal and glial degeneration is significant in multiple sclerosis. Synaptic loss was particularly striking in the neocortical lesions, which should make a major independent contribution to the expression of pathology. New therapies should be directed toward limiting this damage.

Relating functional changes during hand movement to clinical parameters in patients with multiple sclerosis in a multi-centre fMRI study.

We performed a prospective multi‐centre study using functional magnetic resonance imaging (fMRI) to better characterize the relationships between clinical expression and brain function in patients with multiple sclerosis (MS) at eight European sites (56 MS patients and 60 age‐matched, healthy controls). Patients showed greater task‐related activation bilaterally in brain regions including the pre‐ and post‐central, inferior and superior frontal, cingulate and superior temporal gyri and insula (P < 0.05, all statistics corrected for multiple comparisons). Both patients and healthy controls showed greater brain activation with increasing age in the ipsilateral pre‐central and inferior frontal gyri (P < 0.05). Patients, but not controls, showed greater brain activation in the anterior cingulate gyrus and the bilateral ventral striatum (P < 0.05) with less hand dexterity. An interaction between functional activation changes in MS and age was found. This large fMRI study over a broadly selected MS patient population confirms that movement for patients demands significantly greater cognitive ‘resource allocation’ and suggests age‐related differences in brain responses to the disease. These observations add to evidence that brain functional responses (including potentially adaptive brain plasticity) contribute to modulation of clinical expression of MS pathology and demonstrate the feasibility of a multi‐site functional MRI study of MS.

Reproducibility of fMRI in the clinical setting: implications for trial designs

With expanding potential clinical applications of functional magnetic resonance imaging (fMRI) it is important to test how reliable different measures of fMRI activation are between subjects and sessions and between centres. This study compared variability across 17 patients with multiple sclerosis (MS) and 22 age-matched healthy controls (HC) in 5 European centres performing an fMRI block design with hand tapping. We recruited subjects from sites using 1.5 T scanners from different manufacturers. 5 healthy volunteers also were studied at each of 4 of the centres. We found that reproducibility between runs and sessions for single individuals was consistently much greater than between individuals. There was greater run-to-run variability for MS patients than for HC. Measurements of maximum signal change (MSC) appeared to provide higher reproducibility within individuals and greater sensitivity to differences between individuals than region of interest (ROI) suprathreshold voxel counts. The variability in measurements between centres was not as great as that between individuals. Consistent with these observations, we estimated that power should not be reduced substantially with use of multi-, as opposed to single-, centre study designs with similar numbers of subjects. Multi-centre interventional studies in which fMRI is used as an outcome measure thus appear practical even when implemented in conventional clinical environments.

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. Hum Brain Mapp, 2009.

Short-term adaptation to a simple motor task: A physiological process preserved in multiple sclerosis

Short-term adaptation indicates the attenuation of the functional MRI (fMRI) response during repeated task execution. It is considered to be a physiological process, but it is unknown whether short-term adaptation changes significantly in patients with brain disorders, such as multiple sclerosis (MS). In order to investigate short-term adaptation during a repeated right-hand tapping task in both controls and in patients with MS, we analyzed the fMRI data collected in a large cohort of controls and MS patients who were recruited into a multi-centre European fMRI study. Four fMRI runs were acquired for each of the 55 controls and 56 MS patients at baseline and 33 controls and 26 MS patients at 1-year follow-up. The externally cued (1 Hz) right hand tapping movement was limited to 3 cm amplitude by using at all sites (7 at baseline and 6 at follow-up) identically manufactured wooden frames. No significant differences in cerebral activation were found between sites. Furthermore, our results showed linear response adaptation (i.e. reduced activation) from run 1 to run 4 (over a 25 minute period) in the primary motor area (contralateral more than ipsilateral), in the supplementary motor area and in the primary sensory cortex, sensory-motor cortex and cerebellum, bilaterally. This linear activation decay was the same in both control and patient groups, did not change between baseline and 1-year follow-up and was not influenced by the modest disease progression observed over 1 year. These findings confirm that the short-term adaptation to a simple motor task is a physiological process which is preserved in MS.

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.

Measuring and Interpreting White Matter Volume Changes in Multiple Sclerosis

Neuronal and axonal degeneration have become recognized as major elements in the pathology of multiple sclerosis (MS). Interest has developed in monitoring these events in vivo with the recognition that they are closely coupled to development of disability [1]. A compelling question at present is the extent to which these phenomena are linked to the predominantly T-cell-mediated inflammatory changes in white matter (“plaques”), hitherto believed to be the pathological hallmark of MS.