Abnormal corpus callosum integrity in bipolar disorder: a diffusion tensor imaging study

Abstract

Objective: Abnormalities in the anterior interhemispheric connections provided by the corpus callosum (CC) have long been implicated in bipolar disorder (BD). In this study, we used complementary diffusion tensor imaging methods to study the structural integrity of the CC and localization of potential abnormalities in BD.

Methods: Subjects included 33 participants with BD and 40 healthy comparison participants. Fractional anisotropy (FA) measures were compared between groups with region of interest (ROI) methods to investigate the anterior, middle, and posterior CC and voxel-based methods to further localize abnormalities.

Results: In ROI-based analyses, FA was significantly decreased in the anterior and middle CC in the BD group (p < .05). Voxel-based analyses similarly localized group differences to the genu, rostral body, and anterior midbody of CC (p < .05, corrected).

Conclusion: The findings demonstrate abnormalities in the structural integrity of the anterior CC in BD that might contribute to altered interhemispheric connectivity in this disorder.

Figure 1

Sagittal image from the tensor color map displays the left-right coursing fibers of the corpus callosum in red.

Figure 2

Least square (ls) mean anisotropy values in the anterior, middle and posterior corpus callosum and standard errors for the bipolar disorder (BD) group (n = 33) and the healthy comparison (n = 40) group. The difference of ls means indicated that the contribution to group differences was derived mainly from significant decreases in FA in the anterior CC [F(1,142)=8.43, P_Bonf=0.01, Bonferroni corrected for the 3 subregions] and middle CC [F(1,142)=14.6, P_Bonf <0.001] in the BD compared to the HC group; posterior CC FA decreases were not significant [F(1,142)=2.71,P_Bonf=0.3]. Results remained significant when excluding the 2 BD subjects with posttraumatic stress disorder and the subject with panic disorder (effect of diagnosis P<0.001 and in anterior and middle subregions P_Bonf=0.003 and P_Bonf <0.001, respectively). *denotes significant decreases

Figure 3

The sagittal (a, MNI plane: x=−2mm) and coronal (b, MNI plane: y=26mm) images display the genu, rostral body and anterior midbody of the corpus callosum where fractional anisotropy was reduced significantly in participants with bipolar disorder as compared to healthy comparison participants (P<0.005). The color bar represents the range of T values. The findings are displayed in a tissue probability map of white matter.