Alterations in white matter microstructure in bipolar disorder patients with and without psychosis

The overlap of affective disturbance and psychosis considerably makes it complex to determine the etiology of bipolar disorder (BD) and develop targeted interventions. The present study aimed to determine the white matter microstructural alterations that distinguish between BD with psychosis (BDP) and BD with no psychosis (BDNP) to identify patients who may specifically benefit from appropriately effective treatments.

Diffusion-weighted magnetic resonance images were acquired from 38 participants with BDP, 52 participants with BDNP and 70 healthy controls (HCs). The indices of fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (RD) and axial diffusivity (AD) were computed and compared among the three groups via tract-based spatial statistics (TBSS).

Analysis of covariance (ANCOVA) revealed the main effects of group on the FA, MD and RD values of the forceps minor (FMI) of the corpus callosum, right anterior thalamic radiation (ATR), and left corticospinal tract (CST). Post hoc analysis revealed that BDP patients had lower FA value in the FMI than HCs did, as well as lower FA and higher RD values in the FMI than BDNP patients did, whereas BDNP patients had lower FA and MD values in the right ATR, as well as higher FA and lower RD values in the left CST than HCs did.

These findings provide further insights into the specific neurobiological mechanisms that underlie the presence of psychosis in BD patients and represent potential objective biomarkers for differentiating between BDP and BDNP.