Disorder-specific volumetric brain difference in adolescent major depressive disorder and bipolar depression.

Structural abnormalities in frontal, limbic and subcortical regions have been noted in adults with both major depressive disorder (MDD) and bipolar disorder (BD). In the current study, we examined regional brain morphology in youth with MDD and BD as compared to controls. Regional brain volumes were measured in 32 MDD subjects (15.7 ± 2.1 years), 14 BD subjects (16.0 ± 2.4 years) and 22 healthy controls (16.0 ± 2.8 years) using magnetic resonance imaging (MRI). Regions of interest included the hippocampus, dorsolateral prefrontal cortex (DLPFC), anterior cingulate cortex (ACC), caudate, putamen and thalamus. Volumetric differences between groups were significant (F26,80 = 1.80, p = 0.02). Post-hoc analyses indicated that individuals with MDD showed reduced left hippocampus volumes (p = 0.048) as well as right ACC white and gray matter volumes (p = 0.003; p = 0.01) compared to controls. BD participants also displayed reduced left hippocampal and right/left putamen volumes compared to controls (p < 0.001; p = 0.015; p = 0.046 respectively). Interestingly, right and left ACC white matter volumes were smaller in MDD than in BD participants (p = 0.019; p = 0.045 respectively). No volumetric group differences were observed for the DLPFC and thalamus. Discriminant analysis was able to correctly classify 81.0 % of subjects as having BD or as MDD based on imaging data. Confirmation and extension of our findings requires larger sample sizes. Our findings provide new evidence of distinct, specific regional brain volumetric differences between MDD and BD that may be used to distinguish the two disorders.