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Abstract
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.