The relationship between changes in white matter microstructure and cognition in untreated major depressive disorder

White matter (WM) microstructural abnormalities and cognitive impairments are commonly observed in depressive disorders. This study aimed to explore the association between WM microstructural alterations and cognitive function in patients with untreated Major Depressive Disorder (UMDD) compared to healthy controls (HCs).

Sixty-one UMDD patients and sixty-five HCs matched for age, gender, and education underwent diffusion tensor imaging (DTI) using a 3.0 T MRI scanner. Fiber tract-based spatial statistics (TBSS) were applied to analyze WM integrity. Cognitive function was assessed using the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS).

Compared to HCs, UMDD patients exhibited significantly increased axial diffusivity (AD) in the right anterior limb of the internal capsule, splenium of the corpus callosum, right superior longitudinal fasciculus, and body of the corpus callosum. Additionally, mean diffusivity (MD) was elevated in the right superior longitudinal fasciculus. AD values in these regions showed a positive correlation with 24-item Hamilton Rating Scale for Depression (HRSD-24) scores (p ≤ 0.003). MD values in the right superior longitudinal fasciculus were positively correlated with HRSD-24 scores (r = 0.432, p = 0.001) and negatively correlated with RBANS List Learning and Coding scores (p ≤ 0.003).

White matter microstructural abnormalities in UMDD patients are associated with depression severity, suggesting that the underlying structural disruptions are an important indicator of functional abnormalities.