Previous research indicated that gray matter volume (GMV) alterations are associated with mood disorders, but findings have not been consistent in various studies involving adolescents with MDD or bipolar disorder (BD).

In a recent publication in the Journal of Affective Disorders, researchers conducted a comprehensive meta-analysis of 35 region-of-interest (ROI) and 18 whole-brain, voxel-based morphometry (VBM) MRI studies involving adolescents with MDD or BD and indirectly compared the results found between the two groups. Additionally, utilizing meta-regression evaluation, the effects of age, gender, and other demographic factors and clinical scale scores were investigated.

The authors wrote, “In the present study, our first objective was to perform both region-based and whole-brain voxel-based meta-analyses to define the specific GMV alterations, relative to HC [healthy controls], in adolescents with MDD and in adolescents with BD. The second objective was to perform a meta-analytic comparison of these GMV alterations in the two groups; the anisotropic effect-size seed-based d Mapping (AES-SDM) software we used infers this indirect comparison from the pooled effect sizes in the MDD vs. HC and BD vs. HC analyses.”

The results revealed that in the ROI meta-analysis, compared with HCs, right putamen volume was diminished in adolescents with MDD. In contrast, bilateral amygdala volume was reduced in adolescents with BD.

With regard to the whole-brain VBM meta-analysis, compared with HC, GMV was augmented in the right-middle frontal gyrus and reduced in the left caudate in adolescents with MDD. In contrast, GMV was augmented in the left superior frontal gyrus in adolescents with BD and reduced in limbic regions compared with HC. MDD versus BD comparison revealed volume alteration in the prefrontal-limbic system.

The key findings included that adolescents with MDD demonstrated altered GMV compared to controls in the dorsolateral prefrontal cortex and striatum, adolescents with BD showed altered GMV compared to controls in the ventromedial prefrontal cortex and limbic regions, and regions in prefrontal-limbic systems were beneficial in distinguishing adolescents with BD from adolescents with MDD.

The authors concluded that understanding of the distinct patterns of GMV alterations among adolescents with MDD and BD could assist clinicians in distinguishing between these two patient populations and provide them with possible valuable diagnostic biomarkers at an early stage.

They also wrote, “The most notable differences were in the prefrontal-limbic system. Future studies that directly compare adolescents with MDD and adolescents with BD in larger samples size and follow them into adulthood are needed to elucidate the neurobiological trajectories of these important mood disorders.”

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