Cortical thickness associated with past year mood episode in major depressive and bipolar disorders

BACKGROUND: Major depressive disorder and bipolar disorder are affective disorders that carry substantial disease burdens, yet the structural brain alterations due to recent mood episodes remain unclear. To identify acute effects on brain structure, we compared cortical thickness in adults with and without a mood episode in the past year. METHODS: Participants were 30 adults who met lifetime DSM-5 criteria for MDD (n=21) or BD (n=9), divided into a Past Year Mood Episode (PYME) group (n=18), and no-PYME group (n=12). Participants completed the Hamilton Rating Scale for Depression (HAM-D), Young Mania Rating Scale (YMRS) and the semi-structural Longitudinal Interval Follow-up Evaluation (LIFE) interview over the year preceding their structural MRI. RESULTS: The PYME group exhibited greater cortical thickness than the no-PYME group in the left medial orbitofrontal cortex, bilateral V1 primary visual cortex (more extensive in the left hemisphere than the right), left V3 and right V2 visual cortices, and the bilateral hippocampus and left presubiculum. CONCLUSION: Recent mood episodes are linked to increased cortical thickness, possibly reflecting acute compensatory inflammatory responses. Cortical thickness thus shows promise as a transdiagnostic biomarker of recent mood episodes, aiding interpretation of studies that include individuals who are currently euthymic but recently symptomatic.