Hanneke E. Hulst

Regional DTI differences in multiple sclerosis patients

Diffusion tensor imaging (DTI) measures have shown to be sensitive to white matter (WM) damage in multiple sclerosis (MS), not only inside focal lesions but also in user-defined regions in the so-called normal-appearing white matter (NAWM). New analysis techniques for DTI measures are now available that allow for hypothesis-free localization of damage. We performed DTI measurements of 30 MS patients selected for low focal lesion loads, and of 31 age-matched healthy controls and analyzed these using tract-based spatial statistics (TBSS). Patients were found to have a lower fractional anisotropy (FA) compared to controls in a number of brain regions, including the fornices, the left corona radiata, the inferior longitudinal fasciculus in both hemispheres, both optic radiations, and parts of the corpus callosum. In the regions of reduced FA, an increase in radial diffusivity and a less pronounced increase of axial diffusivity were found. Neurocognitive assessment showed that patients had normal visuospatial memory performance, just-normal attention, and impaired processing speed; the latter was associated with abnormal FA in the corpus callosum, an area which was relatively devoid of lesions visible on proton density-weighted images in our patients. TBSS can be useful in future studies with other MS patient samples to provide an unbiased localization of damage and generate location-specific hypotheses.

Brain atrophy and lesion load predict long term disability in multiple sclerosis

Objective To determine whether brain atrophy and lesion volumes predict subsequent 10 year clinical evolution in multiple sclerosis (MS). Design From eight MAGNIMS (MAGNetic resonance Imaging in MS) centres, we retrospectively included 261 MS patients with MR imaging at baseline and after 1–2 years, and Expanded Disability Status Scale (EDSS) scoring at baseline and after 10 years. Annualised whole brain atrophy, central brain atrophy rates and T2 lesion volumes were calculated. Patients were categorised by baseline diagnosis as primary progressive MS (n=77), clinically isolated syndromes (n=18), relapsing–remitting MS (n=97) and secondary progressive MS (n=69). Relapse onset patients were classified as minimally impaired (EDSS=0–3.5, n=111) or moderately impaired (EDSS=4–6, n=55) according to their baseline disability (and regardless of disease type). Linear regression models tested whether whole brain and central atrophy, lesion volumes at baseline, follow-up and lesion volume change predicted 10 year EDSS and MS Severity Scale scores. Results In the whole patient group, whole brain and central atrophy predicted EDSS at 10 years, corrected for imaging protocol, baseline EDSS and disease modifying treatment. The combined model with central atrophy and lesion volume change as MRI predictors predicted 10 year EDSS with R2=0.74 in the whole group and R2=0.72 in the relapse onset group. In subgroups, central atrophy was predictive in the minimally impaired relapse onset patients (R2=0.68), lesion volumes in moderately impaired relapse onset patients (R2=0.21) and whole brain atrophy in primary progressive MS (R2=0.34). Conclusions This large multicentre study points to the complementary predictive value of atrophy and lesion volumes for predicting long term disability in MS.

Cognitive impairment in MS Impact of white matter integrity, gray matter volume, and lesions

Objective: To investigate whether extent and severity of white matter (WM) damage, as measured with diffusion tensor imaging (DTI), can distinguish cognitively preserved (CP) from cognitively impaired (CI) multiple sclerosis (MS) patients. Methods: Conventional MRI and DTI data were acquired from 55 MS patients (35 CP, 20 CI) and 30 healthy controls (HC). Voxelwise analyses were used to investigate fractional anisotropy (FA), mean diffusivity, radial diffusivity, and axial diffusivity of a WM skeleton. Regional gray matter volume was quantified and lesion probability maps were generated. Results: Compared to HCs, decreased FA was found in 49% of the investigated WM skeleton in CP patients and in 76% of the investigated WM in CI patients. Several brain areas that showed reduced FA in both patient groups were significantly worse in CI patients, i.e, corpus callosum, superior and inferior longitudinal fasciculus, corticospinal tracts, forceps major, cingulum, and fornices. In CI patients, WM integrity damage was additionally seen in cortical brain areas, thalamus, uncinate fasciculus, brainstem, and cerebellum. These findings were independent of lesion location and regional gray matter volume, since no differences were found between the groups. Conclusion: CI patients diverged from CP patients only on DTI metrics. WM integrity changes were found in areas that are highly relevant for cognition in the CI patients but not in the CP patients. These WM changes are therefore thought to be related to the cognitive deficits and suggest that DTI might be a powerful tool when monitoring cognitive impairment in MS.

Structural and Functional Hippocampal Changes in Multiple Sclerosis Patients with Intact Memory Function

PURPOSE To investigate changes in hippocampal functional connectivity and structural measures of hippocampal damage in multiple sclerosis (MS) patients with intact spatial memory, a cognitive domain frequently affected in progressive MS. MATERIALS AND METHODS The study protocol was approved by the institutional ethics review board; all subjects gave written informed consent prior to participation. Twenty-five MS patients with intact spatial memory function were compared with 30 age- and sex-matched controls. Hippocampal volume differences, based on manually drawn masks, were evaluated by using the Student t test. Additionally, focal hippocampal lesions and mean diffusivity were obtained as descriptive measures of structural hippocampal damage. Multiple regression analyses of the resting-state functional magnetic resonance (MR) imaging data were performed for each subject by using hippocampal time series. Between-group analyses were conducted with a mixed-effects model, corrected for multiple comparisons by a cluster defining threshold level of z = 2 and a corrected cluster size significance level of P < .05. RESULTS Right hippocampal volume was significantly lower in MS patients as compared with controls (P < .01). Left hippocampal volume was also lower in MS patients compared with controls, but not significantly so (P = .09). Resting-state functional connectivity between the hippocampus and its anatomic input or target areas, including the anterior cingulate gyrus, thalamus, and prefrontal cortex, were significantly decreased in MS patients. Decreased hippocampal functional connectivity was more pronounced in a subgroup of MS patients with hippocampal atrophy, although subtle decreases of functional connectivity were also found in patients with normal hippocampal volume. CONCLUSION In MS patients, substantial abnormalities of hippocampal functional connectivity are already present before spatial memory function is impaired, especially in those patients with more pronounced hippocampal atrophy. Longitudinal studies should now assess whether these functional connectivity and structural changes may precede memory impairment in MS.

Clinical significance of atrophy and white matter mean diffusivity within the thalamus of multiple sclerosis patients.

Background: Gray-matter (GM) atrophy is strongly predictive of cognitive impairment in multiple sclerosis (MS) patients. The thalamus is the region where the atrophy/cognition correlation is most robust. However, few studies have assessed diffusion tensor imaging (DTI) metrics within the thalamus. Objective: This study was designed to determine if thalamus white matter DTI predicts cognitive impairment after accounting for the effects of volume loss. Methods: We enrolled 75 MS patients and 18 healthy controls undergoing 3T brain magnetic resonance imaging (MRI). Thalamus volumes were calculated on 3D T1 images. Voxelwise analyses of DTI metrics were performed within the thalamic white matter tracts. Neuropsychological (NP) testing, acquired using consensus standard methods, contributed measures of memory, cognitive processing speed and executive function. Results: All cognitive tests were significantly predicted (R 2 =0.31, p<0.001) by thalamus volume after accounting for influence of demographics. Mean diffusivity was retained in regression models predicting all cognitive tests, adding from 7–13% of additional explained variance (p<0.02) after accounting for thalamus volume. Conclusions: We confirm the significant role of thalamus atrophy in MS-associated cognitive disorder, and further report that subtle thalamus pathology as detected by DTI adds incremental explained variance in predicting cognitive impairment.

Gender-related differences in functional connectivity in multiple sclerosis

Background: Gender effects are strong in multiple sclerosis (MS), with male patients showing a worse clinical outcome than female patients. Functional reorganization of neural activity may contribute to limit disability, and possible gender differences in this process may have important clinical implications. Objectives: The aim of this study was to explore gender-related changes in functional connectivity and network efficiency in MS patients. Additionally, we explored the association of functional changes with cognitive function. Methods: Sixty subjects were included in the study, matched for age, education level and intelligence quotient (IQ). Male and female patients were matched for disability, disease duration and white matter lesion load. Two cognitive domains often impaired in MS, i.e. visuospatial memory and information processing speed, were evaluated in all subjects. Functional connectivity between brain regions and network efficiency was explored using resting-state functional magnetic resonance imaging and graph analysis. Differences in cognitive and functional characteristics between groups, and correlations with cognitive performance, were examined. Results: Male patients showed worse performance on cognitive tests than female and male controls, while female patients were cognitively normal. Decreases in functional connectivity and network efficiency, observed in male patients, correlated with reduced visuospatial memory (r = −0.6 and r = −0.5, respectively). In the control group, no cognitive differences were found between genders, despite differences in functional connectivity between healthy men and women. Conclusions: Functional connectivity differences were found in male patients only and were related to impaired visuospatial memory. These results underline the importance of gender in MS and require further investigation in larger and longitudinal studies.

Gray matter imaging in multiple sclerosis: what have we learned?

At the early onset of the 20th century, several studies already reported that the gray matter was implicated in the histopathology of multiple sclerosis (MS). However, as white matter pathology long received predominant attention in this disease, and histological staining techniques for detecting myelin in the gray matter were suboptimal, it was not until the beginning of the 21st century that the true extent and importance of gray matter pathology in MS was finally recognized. Gray matter damage was shown to be frequent and extensive, and more pronounced in the progressive disease phases. Several studies subsequently demonstrated that the histopathology of gray matter lesions differs from that of white matter lesions. Unfortunately, imaging of pathology in gray matter structures proved to be difficult, especially when using conventional magnetic resonance imaging (MRI) techniques. However, with the recent introduction of several more advanced MRI techniques, the detection of cortical and subcortical damage in MS has considerably improved. This has important consequences for studying the clinical correlates of gray matter damage. In this review, we provide an overview of what has been learned about imaging of gray matter damage in MS, and offer a brief perspective with regards to future developments in this field.

Functional adaptive changes within the hippocampal memory system of patients with multiple sclerosis

Memory deficits are highly prevalent in multiple sclerosis (MS). As the hippocampus is crucial to memory processing, a functional magnetic resonance imaging (fMRI) task was used to investigate changes in hippocampal function in MS patients with and without cognitive decline. Fifty patients with MS, (34 cognitively preserved (CP) and 16 cognitively impaired (CI)) and 30 healthy controls completed an episodic memory fMRI task (encoding and retrieval) that was used to specifically activate the hippocampus. During encoding of correctly remembered items, increased brain activation was seen in the parahippocampal areas bilaterally and in the left anterior cingulate gyrus in the CP patients compared to the controls (unclustered, Z ≥ 3.1, P ≤ 0.001). No brain areas showed less activation. In CI patients the right (para)hippocampal areas and the prefrontal cortex showed less brain activation compared to controls (cluster‐corrected, P < 0.05). The posterior cingulate gyrus and the left precuneus showed increased activation in CI patients when compared to controls (unclustered Z ≥ 3.1, P ≤ 0.001). No significant differences were found on structural MRI measures between the CP and CI patients. These results suggest the presence of functional adaptation in the memory network before cognitive decline becomes evident in MS, as displayed by the increased brain activation in the hippocampal‐cingulate memory system in CP patients. Interestingly, CI patients showed less activation in the hippocampal network during correct encoding. These findings are important for future cognitive therapeutic studies, since cognitive intervention might be most effective before cognitive impairment is present and when adaptive changes of the brain are most prominent. Hum Brain Mapp 33:2268–2280, 2012.

Thalamus structure and function determine severity of cognitive impairment in multiple sclerosis

Objective: This study investigates whether changes in functional connectivity, diffusivity, and volume of the thalamus can explain different severities of cognitive impairment in multiple sclerosis (MS). Methods: An inception cohort of 157 patients with MS (104 women, mean age 41 years), 6 years postdiagnosis, was divided into 3 groups: cognitively preserved (CP, n = 108), mildly cognitively impaired (MCI, n = 22), and more severely cognitively impaired (SCI, n = 27). These groups were matched to 47 healthy controls (HC, 28 women, mean age 41 years). Thalamic volume, thalamic skeleton diffusivity (fractional anisotropy [FA] and mean diffusivity [MD]), and thalamic resting-state functional connectivity (FC) were compared between groups. Results: Thalamic volume was significantly lower in all patient groups compared to controls, with lowest volumes in patients with SCI, and no difference between CP and MCI. Thalamic skeleton FA was decreased in SCI compared to HC only; MD was increased in SCI compared to all other groups. Thalamic FC was increased in SCI with a total of 15 regions, mainly sensorimotor, frontal, and occipital parts of the brain. Thalamic volume, FC, and MD remained independent predictors in a linear regression model (R2 = 0.46), together with male sex and a lower level of education. Lesion and whole-brain volumes were not significant predictors. Conclusions: These findings indicate that thalamic changes in structure and function are highly informative regarding overall cognitive performance in MS. Increased thalamic FC only became apparent in SCI, possibly as a sign of maladaption.

Functional correlates of cognitive dysfunction in multiple sclerosis: A multicenter fMRI Study

In this multicenter study, we applied functional magnetic resonance imaging (fMRI) to define the functional correlates of cognitive dysfunction in patients with multiple sclerosis (MS). fMRI scans during the performance of the N‐back task were acquired from 42 right‐handed relapsing remitting (RR) MS patients and 52 sex‐matched right‐handed healthy controls, studied at six European sites using 3.0 Tesla scanners. Patients with at least two abnormal (<2 standard deviations from the normative values) neuropsychological tests at a standardized evaluation were considered cognitively impaired (CI). FMRI data were analyzed using the SPM8 software, modeling regions showing load‐dependent activations/deactivations with increasing task difficulty. Twenty (47%) MS patients were CI. During the N‐back load condition, compared to controls and CI patients, cognitively preserved (CP) patients had increased recruitment of the right dorsolateral prefrontal cortex. As a function of increasing task difficulty, CI MS patients had reduced activations of several areas located in the fronto‐parieto‐temporal lobes as well as reduced deactivations of regions which are part of the default mode network compared to the other two groups. Significant correlations were found between abnormal fMRI patterns of activations and deactivations and behavioral measures, cognitive performance, and brain T2 and T1 lesion volumes. This multicenter study supports the theory that a preserved fMRI activity of the frontal lobe is associated with a better cognitive profile in MS patients. It also indicates the feasibility of fMRI to monitor disease evolution and treatment effects in future studies. Hum Brain Mapp 35:5799–5814, 2014.