Charakterisierung mikrostruktureller, kortikaler Pathologie bei Multipler Sklerose mittels Diffusions-Tensor-Bildgebung

Abstract

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system. Typical symptoms are an impaired vision, paresis or sensory disturbances. Conventional magnetic resonance imaging (MRI) techniques are required for the initial diagnosis and visualization of the lesion load, which is mainly located in the white matter. Previous studies assessing cognitive deficits and fatigue in MS patients indicate that also cortical damage is of high clinical relevance in these patients. Insight into cortical damage with conventional MRI techniques is limited. Therefore, in the present study, diffusion tensor imaging (DTI) was used to characterize cortical tissue remodeling in MS. Two tissue parameters were measured: the mean diffusivity (MD) and the fractional anisotropy (FA). Since previous DTI studies in MS reported inconsistent results, the question arose, whether MD and FA changes in patients with relapsingremitting MS (RRMS) can be detected using optimized DTI techniques and how they are distributed across the cortex. 24 patients with RRMS and 25 healthy control subjects participated in this study. MRI acquisition was performed with 3 Tesla MRI scanner. In addition, the clinical status was assessed using the Expanded Disability Status Scale (EDSS). An optimized DTI method with intrinsic eddy current compensation was used. MD and FA maps were created. Cortical parameter values were read and saved in surface-datasets. Global cortical FA/MD values were compared between groups. Furthermore, surface-based statistical comparisons were performed. We tested for correlations between the parameter(s) with significant global group differences and the EDSS. Increased global cortical MD values were observed in the patient group. Surface-based analysis unveiled MD increases particularly in temporal, occipital and parietal regions. Furthermore, the MD correlated significantly with the EDSS score. In addition, we observed focal cortical FA decreases in the temporal and occipital lobes. The MD correlates positively with the amount of diffusion in a certain area. Diffusion is limited by microstructural barriers. Accordingly, MD might quantify the integrity microstructural barriers. FA values are high inordered structures with directional diffusion such as fiber tracts. Therefore, reduced FA values in the occipital and temporal cortical might reflect axonal damage. Regions with MD increase were more widespread than areas with FA reduction. This finding might indicate that the cortical breakdown of microstructural barriers in MS patients is a more prominent and widespread cortical remodeling mechanism than the disruption of axonal structures. In addition, the observed correlation between cortical MD values and the EDSS highlights a potential relevance of DTI techniques for larger clinical studies.