Diffusion tensor imaging and cognitive speed in children with multiple sclerosis.

OBJECTIVES: To compare white matter (WM) integrity in children with MS and healthy children using diffusion tensor imaging (DTI), and correlate DTI findings with disease activity, lesion burden, and cognitive processing speed.
METHODS: Fractional anisotropy (FA) and mean diffusivity (MD) in normal-appearing white matter (NAWM) were measured in four corpus callosum (CC), eight hemispheric regions, and the normal-appearing thalamus of 33 children and adolescents with MS and 30 age-matched healthy controls. Images were acquired on a GE LX 1.5T scanner. DTI parameters used were 25 directions, b = 1000 s/mm(2), and 5mm slice thickness. MS patients had T2 lesion volumes and Expanded Disability Status Scale (EDSS) scores were measured; all participants underwent two speeded cognitive tasks (Visual Matching and Symbol Digit Modalities Test (SDMT)).
RESULTS: MS participants displayed lower FA values in the genu (p<0.005), splenium (p<0.001) and in NAWM of bilateral parietal, temporal, and occipital lobes (p<0.001) versus controls. FA and MD in the thalamus did not differ between groups. Higher lesion volumes correlated with reduced FA in CC and hemispheric NAWM. DTI metrics did not correlate with EDSS. FA values in CC regions correlated with Visual Matching (p<0.001) and SDMT (p<0.005) in MS participants only.
INTERPRETATION: DTI analyses indicate widespread NAWM disruption in children with MS-with the degree of abnormality correlating with impaired cognitive processing speed. These findings support an early onset tissue pathology in MS and illustrate its functional consequence.