White matter abnormalities distinguish childhood-onset BD

By Mark Cowen, Senior MedWire Reporter

Increased white matter microstructure abnormalities may differentiate pediatric- from adult-onset bipolar disorder (BD), results from a US study suggest.

In a brain imaging study of white matter tracts, researchers found that BD patients with pediatric-onset disease had significantly reduced fractional anisotropy (FA) values in the left anterior limb of the internal capsule (ALIC) compared with those with adult-onset BD.

"The greater pathology of the ALIC in childhood-onset cases suggested that the pathophysiology of BD in childhood may be more severe or perhaps differs in fundamental ways from that in patients with a later onset of disease," comment Lisa Lu (University of Illinois at Chicago) and team.

The findings come from a diffusion tensor imaging study of 35 individuals, aged 11-42 years, with a first episode of BD and 46 mentally healthy controls, aged 9-37 years. There were no significant differences between the groups regarding mean age, gender distribution, handedness, or IQ.

The researchers found that the BD group as a whole showed significantly reduced FA values in the left ALIC after correction for multiple comparisons. And these reductions were significantly greater in BD patients with pediatric-onset disease (n=19) than in those with adult-onset disease.

White matter tracts that showed a trend-level deviation in FA values in younger compared with older BD patients included the bilateral anterior corona radiata, posterior corona radiata, posterior limb of the internal capsule, retrolenticular part of the internal capsule, left sagittal stratum, left external capsule, and right superior corona radiata.

Post-hoc analyses indicated that lower FA values in BD patients compared with controls was mostly due to increased radial, rather than decreased axial, diffusivity.

Lu and team comment in Bipolar Disorders: "The ALIC connects the frontal lobes with archistriatum, thalamus, and medial temporal regions, and alteration in these pathways may contribute to mood dysregulation in BD.

"Abnormalities in this pathway appear to be associated with an earlier onset of illness and thus may reflect a greater susceptibility to illness."

They add: "Future studies are needed to evaluate the full extent of age-related white-matter alterations throughout the brain in BD."

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