Diffusion tensor imaging study of white matter fiber tracts in pediatric bipolar disorder and attention-deficit/hyperactivity disorder

Abstract

Background: To investigate microstructure of white matter fiber tracts in pediatric bipolar disorder (PBD) and attention-deficit/hyperactivity disorder (ADHD).

Methods: A diffusion tensor imaging (DTI) study was conducted at 3 Tesla on age- and IQ-matched children and adolescents with PBD (n = 13), ADHD (n = 13), and healthy control subjects (HC) (n = 15). Three DTI parameters, fractional anisotropy (FA), apparent diffusion coefficient (ADC), and regional fiber coherence index (r-FCI), were examined in eight fiber tracts: anterior corona radiata (ACR), anterior limb of the internal capsule (ALIC), superior region of the internal capsule (SRI), posterior limb of the internal capsule (PLIC), superior longitudinal fasciculus (SLF), inferior longitudinal fasciculus (ILF), cingulum (CG), and splenium (SP).

Results: Significantly lower FA was observed in ACR in both PBD and ADHD relative to HC. In addition, FA and r-FCI values were significantly lower in ADHD relative to PBD and HC in both the ALIC and the SRI. Further, ADC was significantly greater in ADHD relative to both the PBD and HC in ACR, ALIC, PLIC, SRI, CG, ILF, and SLF.

Conclusions: Decreased FA in ACR implies an impaired fiber density or reduced myelination in both PBD and ADHD in this prefrontal tract. These abnormalities, together with the reduced fiber coherence, extended to corticobulbar tracts in ADHD. Increased ADC across multiple white matter tracts in ADHD indicates extensive cellular abnormalities with less diffusion restriction in ADHD relative to PBD.

Figure 1

DTI images illustrating the eight White Matter (WM) tracts measured in this study. Anterior corona radiata (ACR) - WM tract extending from dorsolateral and ventrolateral prefrontal cortex primarily to pretectum. WM fibers of the internal capsule including: Anterior limb of the internal capsule (ALIC), Superior region of the internal capsule (SRI) and Posterior limb of the internal capsule (PLIC); Superior longitudinal fasciculus II (SLF II) which connects the PFC and the caudal inferior parietal lobule; Inferior longitudinal fasciculus (ILF) comprised of U-shaped fibers connecting extrastriate visual association areas and temporal regions involved in transfering visual signals to anterior temporal regions and also including projections from amygdala to early visual areas; Cingulum bundle (CG) that includes WM fibers that connect to prefrontal cortex, anterior cingulate cortex, thalamus and somatosensory regions; Splenium (SP) including posterior bulb of the corpus callosum that joins the posterior cortical regions across the cerebral hemispheres. For all regions, with the exception of SP, the ADHD group exhibited significantly greater values than the other two groups, which did not differ from each other. For SP only, the ADHD and PBD groups did not differ from each other, and exhibited greater values than HC. *p<0.001; **p<0.001.