Microstructural analyses of the posterior cerebellar lobules in relapsing-onset multiple sclerosis and their implication in cognitive impairment

Fronto-striatal damage may contribute to resistance to fatigue-lowering medications in multiple sclerosis

BACKGROUND AND PURPOSE

Commonly used fatigue-lowering medications have not been proven effective in treating multiple sclerosis (MS)-related fatigue. A neuroanatomical basis for treatment-resistant fatigue in MS has not been explored. The aim of this study was to investigate the association between brain diffusion abnormality patterns and resistance to fatigue-lowering treatment.

METHODS

Retrospective patient stratification: 1. treatment-resistant (n = 22) received anti-fatigue and/or anti-depressant and/or anxiolytic medication and the latest two Modified Fatigue Impact Scale (MFIS) score≥38; 2. responder (n = 16): received anti-fatigue and/or antidepressant and/or anxiolytic medication while the latest MFIS was <38, and minimum one previous MFIS was ≥38; 3. non-treated never-fatigued (n = 26): received none of the above-mentioned medications and MFIS was always<38 (over minimum four years assessed with MFIS every 1-2 years). 3T brain MRI was used to perform a cross-sectional voxel-wise comparison of fractional anisotropy (FA) between the groups.

RESULTS

Treatment-resistant versus responder patients showed more extensive brain damage (ie, lower FA) favoring the fronto-striatal pathways. Both groups showed more widespread brain damage than non-treated never-fatigued patients. A mean fronto-striatal FA value of 0.26 could perfectly predict response to modafinil/armodafinil.

CONCLUSION

Fronto-striatal damage may play a role in the development of resistance to fatigue-lowering treatment. Fronto-striatal FA may serve as a biomarker to predict response to fatigue-lowering medications in MS.

Microstructural White Matter Alterations in Cognitively Impaired Patients at Early Stages of Multiple Sclerosis

PURPOSE

As conventional quantitative magnetic resonance imaging (MRI) parameters are weakly associated with cognitive impairment (CI) in early multiple sclerosis (MS), we explored microstructural white matter alterations in early MS or clinically isolated syndrome (CIS) comparing patients with or without CI.

METHODS

Based on a preceding tract-based spatial statistics analysis (3 Tesla MRI) which contrasted 106 patients with early MS or CIS and 49 healthy controls, diffusion metrics (fractional anisotropy, FA, mean diffusivity, MD) were extracted from significant clusters using an atlas-based approach. The FA and MD were compared between patients with (Ci_P n = 14) and without (Cp_P n = 81) cognitive impairment in a subset of patients who underwent CI screening.

RESULTS

The FA was reduced in Ci_P compared to Cp_P in the splenium of corpus callosum (p = 0.001), right parahippocampal cingulum (p = 0.002) and fornix cres./stria terminalis (0.042), left posterior corona radiata (p = 0.012), bilateral cerebral peduncles, medial lemniscus and in cerebellar tracts. Increased MD was detected in the splenium of corpus callosum (p = 0.01). The CI-related localizations overlapped only partially with MS lesions.

CONCLUSION

Microstructural white matter alterations at disease onset were detectable in Ci_P compared to Cp_P in known cognitively relevant fiber tracts, indicating the relevance of early treatment initiation in MS and CIS.

Default Mode Network Structural Integrity and Cerebellar Connectivity Predict Information Processing Speed Deficit in Multiple Sclerosis

Cognitive impairment affects about 50% of multiple sclerosis (MS) patients, but the mechanisms underlying this remain unclear. The default mode network (DMN) has been linked with cognition, but in MS its role is still poorly understood. Moreover, within an extended DMN network including the cerebellum (CBL-DMN), the contribution of cortico-cerebellar connectivity to MS cognitive performance remains unexplored. The present study investigated associations of DMN and CBL-DMN structural connectivity with cognitive processing speed in MS, in both cognitively impaired (CIMS) and cognitively preserved (CPMS) MS patients. 68 MS patients and 22 healthy controls (HCs) completed a symbol digit modalities test (SDMT) and had 3T brain magnetic resonance imaging (MRI) scans that included a diffusion weighted imaging protocol. DMN and CBL-DMN tracts were reconstructed with probabilistic tractography. These networks (DMN and CBL-DMN) and the cortico-cerebellar tracts alone were modeled using a graph theoretical approach with fractional anisotropy (FA) as the weighting factor. Brain parenchymal fraction (BPF) was also calculated. In CIMS SDMT scores strongly correlated with the FA-weighted global efficiency (GE) of the network [GE(CBL-DMN): ρ = 0.87, R² = 0.76, p < 0.001; GE(DMN): ρ = 0.82, R² = 0.67, p < 0.001; GE(CBL): ρ = 0.80, R² = 0.64, p < 0.001]. In CPMS the correlation between these measures was significantly lower [GE(CBL-DMN): ρ = 0.51, R² = 0.26, p < 0.001; GE(DMN): ρ = 0.48, R² = 0.23, p = 0.001; GE(CBL): ρ = 0.52, R² = 0.27, p < 0.001] and SDMT scores correlated most with BPF (ρ = 0.57, R² = 0.33, p < 0.001). In a multivariable regression model where SDMT was the independent variable, FA-weighted GE was the only significant explanatory variable in CIMS, while in CPMS BPF and expanded disability status scale were significant. No significant correlation was found in HC between SDMT scores, MRI or network measures. DMN structural GE is related to cognitive performance in MS, and results of CBL-DMN suggest that the cerebellum structural connectivity to the DMN plays an important role in information processing speed decline.

Differential Gray Matter Vulnerability in the 1 Year Following a Clinically Isolated Syndrome

Background and purpose: Whether some gray matter (GM) regions are differentially vulnerable at the early stages of MS is still unknown. The objective of this study is to investigate whether deep and cortical GM are differentially vulnerable after a clinically isolated syndrome (CIS) suggestive of multiple sclerosis (MS).

Methods: Fifty-six patients with CIS (PwCIS) and 38 healthy controls (HC) had conventional and diffusion tensor imaging (DTI) at baseline and 46 PwCIS and 20 HC were rescanned after 1 year. Deep GM (DGM) volumes, cortical thickness (CTh), and DTI metrics (FA: fractional anisotropy; MD: mean diffusivity) within these structures were calculated for each participant at each time-point and compared between PwCIS and HC. Linear regression models were used to investigate whether baseline DTI parameters could predict GM volume loss over time.

Results: At baseline, GM volumes did not differ between PwCIS and HC, but hippocampal MD was higher in PwCIS than HC (p < 0.01). Over 1 year, GM alterations became more widespread with putamen and hippocampus volumes decreasing in PwCIS (p < 0.01), and cortical thinning in different parts of the cortex along with a significant increase of MD. Hippocampus MD at baseline could predict its volume loss (R² = 0.159; p < 0.05) and cortical thinning was associated to microstructural damage (Spearman's rho ranging from −0.424 to −0.603 with p < 0.003).

Conclusion: Along with MS being a diffuse inflammatory disease, GM showed a differential vulnerability at the early stage spreading from hippocampus to the cortex. Hippocampus volume loss could be predicted by its MD at baseline.

Cerebellum and cognition in progressive MS patients: functional changes beyond atrophy?

BACKGROUND

The cerebellum is a predilection site of pathology in progressive multiple sclerosis (PMS) patients, contributing to cognitive deficits. Aim of this study was to investigate lobular cerebellar functional connectivity (FC) in PMS patients in relation to cognition.

METHODS

In this cross-sectional study, resting state fMRI analysis was carried out on 29 PMS patients (11 males, mean age 51.2 ± 11.9 years) and 22 age- and sex-matched healthy controls (HC) (11 males, mean age 49.6 ± 8.8 years). Data were analyzed with a seed-based approach, with four different seeds placed at the level of cerebellar Lobule VI, Crus I, Crus II and Lobule VIIb, accounting for cerebellar structural damage. Cognitive status was assessed with the BICAMS battery. Correlations between fMRI data and clinical variables were probed with the Spearman correlation coefficient.

RESULTS

When testing FC differences between PMS and HC without taking into account cerebellar structural damage, PMS patients showed a reduction of FC between Crus II/Lobule VIIb and the right frontal pole (p = 0.001 and p = 0.002, respectively), with an increased FC between Lobule VIIb and the right precentral gyrus (p < 0.001). After controlling for structural damage, PMS patients still showed a reduced FC between Crus II and right frontal pole (p = 0.005), as well as an increased FC between Lobule VIIb and right precentral gyrus (p = 0.003), with the latter showing an inverse correlation with BVMT scores (r = - 0.393; p = 0.03).

CONCLUSION

PMS patients show cerebellar FC rearrangements that are partially independent from cerebellar structural damage, and are likely expression of a maladaptive functional rewiring.

Brain connectivity and cognitive processing speed in multiple sclerosis: A systematic review

BACKGROUND

Processing speed (PS) decline is the most commonly observed cognitive deficit in people with multiple sclerosis (MS) resulting in a significant impact on quality of life. Despite its importance, knowledge of the underlying neural substrates is lacking.

OBJECTIVE

As MS is increasingly recognised as a disconnection syndrome, our aim was to carry out a systematic literature review to clarify the relationship between PS performance and MRI measures of structural and functional brain connectivity in people with MS.

SEARCH METHODS

A literature search was carried out on PubMed and Web of Science that included publications predating September 2017. Additional articles were added after inspection of the reference lists of all selected papers.

DATA EXTRACTION

All selected papers were categorised in three sections according to the MRI measures investigated, independently or both. Quality assessment was carried out using a customised set of criteria.

RESULTS

Thirty-two articles met the inclusion criteria and were included in the review. Microstructural integrity of the anterior corpus callosum and functional connectivity of frontal areas were more consistently found to correlate with PS performance, though high variability of findings was observed across studies. Several methodological flaws emerged from the reviewed literature.

CONCLUSIONS

Despite the observed trends, no definite conclusions can be drawn on the relationship between brain connectivity and PS decline in MS given the limitations of the current literature. Future investigations may benefit from theoretical and methodological advances to clarify how MS-related brain damage affects patients' cognition.