Background: Changes of white matter (WM) microstructure have been proposed as structural biomarkers of bipolar disorder (BD). The chronotherapeutic combination of repeated total sleep deprivation and morning light therapy (TSD+LT) can acutely reverse depressive symptoms in approximately 60% of patients, and it has been proposed as a model antidepressant treatment to investigate the neurobiological correlates of rapid antidepressant response.
Methods: We tested if baseline DTI measures can predict response to treatment in 70 in-patients affected by a major depressive episode in the course of BD, treated with chronotherapeutics for one week. We performed whole-brain tract-based spatial statistics with threshold-free cluster enhancement for the DTI measures of WM microstructure integrity: fractional anisotropy, axial, radial, and mean diffusivity.
Results: Increased mean and radial water diffusivity correlated with poor antidepressant response to TSD+LT in core WM tracts which are crucial for the functional integrity of the brain, including corpus callosum, corona radiata, cingulum bundle, superior longitudinal fasciculus, inferior fronto-occipital fasciculus, and thalamic radiation.
Limitations: Limitations include issues such as generalizability, possible population stratification, medications and their effects on DTI measures, and no placebo control for chronotherapeutics. We could not consider other factors such as gene-environment interactions.
Conclusions: The association of increased radial and mean diffusivity with poor response to chronotherapeutic treatment warrants interest for the study of DTI measures of WM microstructure as markers for treatment response in bipolar depression.
Keywords: Antidepressant; Biomarker; Bipolar disorder; Chronotherapeutics; Diffusion tensor imaging; White matter.
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