White matter microstructural characteristics in Bipolar I and Bipolar II Disorder: A diffusion tensor imaging study.

Area of Science:

• Neuroimaging
• Neuroscience
• Psychiatry

Background:

• Diffusion tensor imaging (DTI) studies in bipolar disorder (BD) yield inconsistent findings, with a focus on bipolar I (BD-I).
• Investigating differences between bipolar I (BD-I) and bipolar II (BD-II) using DTI is crucial for understanding subtype-specific brain alterations.

Purpose of the Study:

• To compare diffusion tensor imaging (DTI) parameters between bipolar I (BD-I) and bipolar II (BD-II) disorder.
• To identify differences in white matter integrity between bipolar disorder (BD) subtypes and healthy controls (HC).

Main Methods:

• Tract-based spatial statistics (TBSS) analysis of DTI parameters: fractional anisotropy (FA), axial diffusivity (AD), and radial diffusivity (RD).
• A matched sample of 50 BD patients (25 BD-I, 25 BD-II) and 50 healthy controls (HC) were included.
• Analysis focused on chronic-phase BD patients.

Main Results:

• Bipolar II disorder (BD-II) exhibited lower FA in the right inferior longitudinal fasciculus (ILF) compared to BD-I and HC.
• Both BD subtypes showed reduced AD and RD in the left internal capsule and cerebellum compared to HC.
• Lower AD was observed in the left ILF and right corticospinal tract in both BD groups relative to HC.

Conclusions:

• Bipolar II disorder (BD-II) patients demonstrate unique white matter (WM) alterations in the ILF compared to BD-I.
• Widespread WM changes in the internal capsule, corticospinal tract, and cerebellum are present in both BD subtypes.
• WM integrity loss in BD-II may involve demyelination, while shared changes in both subtypes could indicate axonal damage.