This study aimed to investigate alterations in white matter microstructure in patients with psychotic and non-psychotic bipolar disorder (PBD and NPBD, respectively). We used 3T-magnetic resonance imaging to examine 29 PBD, 23 NPBD, and 65 healthy control (HC) subjects. Using tract-based spatial statistics for diffusion tensor imaging data, we compared fractional anisotropy and mean diffusion pairwise among the PBD, NPBD, and HC groups. We found several white matter areas of decreased fractional anisotropy or increased mean diffusion in the PBD and NPBD groups compared to HC. PBD showed widespread fractional anisotropy decreases in the corpus callosum as well as the bilateral internal capsule and fornix. However, NPBD showed local fractional anisotropy decreases in a part of the corpus callosum body as well as in limited regions within the left cerebral hemisphere, including the anterior and posterior corona radiata and the cingulum. In addition, both PBD and NPBD shared widespread mean diffusion increases across the posterior corona radiata, cingulum, and sagittal stratum. These findings suggest that widespread white matter microstructural alterations might be a common neuroanatomical characteristic of bipolar disorder, regardless of being psychotic or non-psychotic. Particularly, PBD might involve extensive inter-and intra-hemispheric white matter connectivity disruptions.

MRI data were acquired using a 3-Tesla MRI scanner (Ingenia CX; Philips, Erlangen) equipped with a 32-channel head coil at National Center for Mental Health. A diffusion-weighted image was acquired using single-shot echo-planar imaging sequence with the following parameters: acquisition matrix = 128 × 128, voxel size = 1.75 × 1.75 × 2 mm³, axial slices = 72, FOV = 224 × 224 mm², TE = 90 ms, TR = 9000 ms, flip angle = 90°, slice gap = 0 mm, b-value = 0 and 1000 s/mm², and diffusion sensitive gradient direction = 64. The baseline image without weighting was used [0, 0, 0].