Diffusion tensor imaging correlates of depressive symptoms in Parkinson disease

Depression is a heterogeneous clinical syndrome prevalent in patients with Parkinson disease (PD) that remains incompletely understood. Further, the differences in biomarkers of depression in PD and in non-PD patients are unclear. The subcallosal cingulate cortex (SCC) and its connections have been implicated in the pathophysiology of major depressive disorder (MDD). Diffusion tensor imaging (DTI) provides a tool to quantify MDD-related structural abnormalities underlying depressive symptoms in PD. Diffusion-weighted magnetic resonance imaging data were collected from 31 patients with PD. Depression symptom severity was measured using the Beck Depression Inventory (BDI-II), and assessed using three subscales: dysphoric mood, loss of interest/pleasure, and somatic symptoms. Probabilistic tractography methods were used to quantify the SCC connectivity to target regions in cortico-limbic-striatal network (ventral striatum, medial prefrontal cortex [mPFC], dorsal anterior cingulate cortex, and uncinate fasciculus), while fractional anisotropy (FA) was calculated in predefined white matter regions of interest. DTI data were correlated with severity of depression across three domains. SCC-mPFC connectivity in the left hemisphere was positively correlated with severity of dysphoric mood (Benjamini-Hochberg adjusted p = .02). Region of interest-based analyses demonstrated a significant and distinct topographic association between FA and dysphoric mood, loss of interest/pleasure, and somatic symptom severity, although these findings did not maintain significance after applying the false discovery rate correction. Abnormal SCC connectivity underlies depressive symptoms in both PD and MDD, suggesting that interventions used for MDD should be explored in treating depressive symptoms in PD, particularly depression dominated by dysphoric mood.