A meta-analysis of whole-brain diffusion tensor imaging studies in bipolar disorder

White matter abnormalities are one of the most consistently reported findings in neuroimaging studies of bipolar disorder (BD). We conducted an anatomical likelihood estimation meta-analysis of BD whole-brain diffusion tensor imaging (DTI) studies, with the aim of identifying statistically consistent fractional anisotropy (FA) changes reflecting microstructural modifications to white matter in BD.

We performed online searches of the PUBMED and EMBASE databases in January 2011. Studies were considered for inclusion if they used diffusion tensor MRI, compared a group of subjects with BD with healthy controls and involved whole-brain white matter analysis of FA. The analyses were conducted in Talairach space, using the activation likelihood estimation technique. We carried out a meta-analysis restricted to studies reporting a lower FA in patients with BD than in healthy controls.

Ten studies were included. We identified two significant clusters of decreased FA on the right side of the brain. The first was located in the right white matter, close to the parahippocampal gyrus. Four of the ten studies included contributed to this cluster. The second cluster was located close to the right anterior and subgenual cingulate cortex. These two clusters of decreased FA in BD are crossed by several white matter tracts.

These two clusters of altered FA may underlie the abnormal emotional processing and altered functional limbic connectivity in BD. Explorations based on DTI-based tractography are required to identify the tracts involved in the pathophysiology of BD.