Gray matter, white matter, brain, and intracranial volumes in first-episode bipolar disorder: a meta-analysis of magnetic resonance imaging studies

Objectives: To perform a comprehensive quantitative analysis of the existing magnetic resonance imaging (MRI) studies of the brain conducted on patients with first-episode bipolar disorder (BD). Methods: A systematic search was performed of MRI studies that reported quantitative measurements of brain volumes of first-episode bipolar patients and healthy controls. Four meta-analyses were performed for four cerebral regions. Results: Significant overall effect sizes were demonstrated, with a reduction detected in patients with BD for total intracranial and white matter volumes, but not for gray matter and whole brain volumes. Conclusions: The available MRI literature indicates that specific structural brain abnormalities are already present in first-episode bipolar patients. These do not overlap with those emerging from previous meta-analyses performed in patients with chronic BD. These findings support the hypothesis of different patterns of changes in brain morphology over the time course of bipolar disorder.