Brain microstructure alterations in bipolar disorder subtypes revealed by diffusion kurtosis imaging

Bipolar disorder (BD) is often associated with extensive changes in white matter (WM) microstructure. While diffusion tensor imaging (DTI) has been used in BD studies, diffusion kurtosis imaging (DKI) has rarely been explored, particularly concerning the different subtypes of BD. This cross-sectional study compared DTI and DKI metrics of the brain WM in participants with BD type I (BD-I) and II (BD-II) and in healthy controls (HC). The correlation between the diffusion metrics and the clinical scores was examined. In total, 40 patients with BD and 42 HC were enrolled. Diffusion metrics across groups were examined using tract-based spatial statistics. Patients with BD-I showed lower fractional anisotropy and kurtosis values throughout the WM compared with the values found in patients with BD-II and HC. Comparison between the BD subtypes suggested that patients with BD-I had more prominent WM disruption. Diffusion kurtosis imaging analyses demonstrated a greater spatial extent of significant effects across different BD subtypes than could be achieved by DTI. Our results indicated that DKI can enhance the sensitivity to WM microstructural alterations in BD and that this technique can provide valuable insights into the biological differences between BD-I and BD-II.