Simple developmental dyslexia in children: alterations in diffusion-tensor metrics of white matter tracts at 3 T

To determine whether there are detectable differences in tensor metrics between children who read normally and children with simple developmental dyslexia and/or differences between the right and left hemispheres in these groups by using 3.0-T diffusion-tensor (DT) magnetic resonance (MR) imaging focused on the superior longitudinal fasciculus (SLF), inferior fronto-occipital and inferior longitudinal fasciculi (IFO-ILF), and posterior limb of the internal capsule (PLIC).

This was a prospective, HIPAA-compliant institutional review board-approved investigation with written informed parental consent. Nineteen English-speaking, right-handed children with a normal IQ and developmental dyslexia (16 male, three female; age range, 6-16 years; mean age, 9.9 years) and 18 normal-reading, age-matched pediatric control subjects (13 male, five female; age range, 6-15 years; mean age, 10.0 years) underwent DT imaging (30 directions, three signals acquired, voxel size of 2 mm). Regions of interest were placed on the SLF, IFO-ILF, and PLIC, and tensor metrics were calculated. Statistical analyses of differences in cognitive function between the dyslexic and control groups were performed by using the two-sample t test. Differences in tensor metrics were examined by using analysis of covariance models.

In the control subjects, the fractional anisotropy (FA) of all tracts studied increased with age. In the dyslexic subjects, the age-related increases in FA in the SLF were most similar to those in the control subjects (P = .504), while mean FA values for the IFO-ILF (P = .009) and PLIC (P < .0001) were higher than those in the control subjects up to around 11 years of age, after which they were lower. Apparent diffusion coefficients consistently decreased in both groups. There was a nonsignificant increase in mean axial diffusivity in the IFO-ILF in the control group but not in the dyslexia group. Increases in axial diffusivity seen in the PLIC in the control group were not seen in the dyslexia group. There were no marked differences in tensor metrics between the left and right hemispheres within or between the two groups.

Findings at 3.0-T DT imaging suggest that white matter differences in dyslexic children are not limited to the portion of the brain traditionally considered to be integral to word recognition and processing.