Cortical Thickness and Subcortical Volumes in Schizophrenia and Bipolar Disorder

Background: Schizophrenia and bipolar disorder are severe psychiatric diseases with overlapping symptomatology. Widespread brain morphologic abnormalities, including cortical thinning and subcortical volume reductions, have been demonstrated in schizophrenia but it is unclear whether similar abnormalities are present in bipolar disorder. The purpose of this study was to compare cortical thickness and subcortical volumes in schizophrenia and bipolar disorder, to assess differences and similarities in cortical and subcortical brain structure. Methods: We analyzed magnetic resonance images from a sample of 173 patients with schizophrenia spectrum disorder, 139 patients with bipolar disorder, and 207 healthy control subjects. Cortical thickness was compared between the groups in multiple locations across the continuous cortical surface. Subcortical volumes were compared on a structure-by-structure basis. Results: There was widespread cortical thinning in schizophrenia compared with control subjects, in frontal, temporal, occipital, and smaller parietal regions. There was no cortical thinning in bipolar disorder compared with control subjects or in schizophrenia compared with bipolar disorder. However, the subgroup of patients with bipolar disorder Type 1 showed cortical thinning, primarily in the frontal lobes and superior temporal and temporoparietal regions. Both patient groups showed substantial subcortical volume reductions bilaterally in the hippocampus, the left thalamus, the right nucleus accumbens, the left cerebellar cortex, and the brainstem, along with substantial ventricular enlargements. Conclusions: We found substantial overlap in the underlying brain morphologic abnormalities in schizophrenia and bipolar disorder in subcortical structures, and between schizophrenia and bipolar disorder Type 1 in the cerebral cortex.