Cortical thickness signature as a predictor of diagnostic transition from major depressive disorder to bipolar disorder in late adolescence and early adulthood: a prospective nested case-control study.

BACKGROUND

Bipolar disorder (BD) and major depressive disorder (MDD) are classified as distinct diagnostic categories. However, early identification of BD from MDD is challenging due to their high overlap in clinical features, particularly in late adolescence and early adulthood. This study aimed to explore biomarkers for the early identification of BD from MDD.

METHODS

The study consists of 139 BD, 148 unipolar depression (UD), and 128 healthy controls (HC) participants ranging from late adolescence to early adulthood. In addition, an independent group of 62 patients initially diagnosed with MDD at baseline and transitioned to BD during follow-up was identified as initial depressive episode BD (IDE-BD). Cortical thickness and surface area were measured for all participants, along with the associations with clinical symptoms.

RESULTS

IDE-BD shares similar cortical thickness patterns with BD and UD. Compared to HC, cortical thinning in the left inferior temporal cortex was observed across all depressive episode groups. Cortical thickness alterations in the right caudal anterior cingulate cortex (cACC.R) were observed specifically in the BD and IDE-BD but were absent in the UD. Compared to UD, IDE-BD exhibited significantly increased cortical thickness in the cACC.R. Moreover, the increase in cACC.R thickness in the IDE-BD was associated with hypomania and suicide risk scores.

CONCLUSIONS

In this cross-diagnostic study focusing on late adolescence and early adulthood, we found evidence suggesting shared and disease-specific cortical thickness patterns of depressive episodes. Our study offers potential insights into the neuropathological mechanisms of mood disorders and may contribute to the early identification of BD from MDD.