Abstract
Objective: Neuroimaging studies of bipolar disorders have provided an insight into the pathophysiology, and have raised an issue of a shared change with schizophrenia and the normalizing effect of lithium on the alteration. Despite the classification of the bipolar disorders into the bipolar I disorder (BP-I) and bipolar II disorder (BP-II), the patients with BP-II have only been involved in a limited number of the neuroimaging studies. There is minimal information about the direct comparison between BP-II and schizophrenia. Methods: All patients were diagnosed using DSM-5 criteria. A cross-sectional study was carried out to compare the regional brain volumes among the patients with BP-II taking lithium (BP-II-On, n=17) and not taking it (BP-II-Off, n=22), the patients with schizophrenia (n=35) and healthy controls (n=36). The MRI data were processed using Statistical Parametric Mapping 8 and the divided brain areas were defined by an automated anatomical labeling. Results: A significant reduction in the gray matter volume of the frontal, temporal and limbic lobes was similarly observed in BP-II-off and schizophrenia patients when compared to the controls. The brain volume of BP-II-On had significantly decreased in the temporal lobe, but not in either the frontal or limbic lobe. The less pronounced reduction of BP-II-On was also observed in the sub-regions of the prefrontal and limbic cortices, such as the anterior cingulate cortex. Conclusion: The present study suggests that there was a similarity in the distribution pattern of the decreased gray matter volume in the brain between BP-II and schizophrenia, placing an emphasis on the lithium effect that putatively normalized the abnormality in the anterior frontal and limbic brain areas of BP-II. However, further studies are required to replicate the results in a larger cohort and to confirm the lithium effect in a longitudinal study.
Highlights
The pathophysiology of psychiatric disorders may underlie an abnormality in the brain structure constituting the functional neural circuitry [1,2]
At the time of the MRI scanning session, patients with bipolar II disorder (BP-II) were evaluated by the Hamilton Rating Scale for Depression-17 items (HAMD) and the Young Mania Rating Scale (YMRS), while patients with schizophrenia were assessed by the Positive and Negative Syndrome Scale (PANSS) [37]
The score of the 17-item HAMD or the YMRS did not differ between the two BP-II groups in the MRI study
Summary
The pathophysiology of psychiatric disorders may underlie an abnormality in the brain structure constituting the functional neural circuitry [1,2]. Studies employing the neuroimaging technique have revealed a significant change in bipolar disorders [2,3,4,5,6,7,8] as well as schizophrenia [9,10], showing a potential overlap of the structural abnormalities in the front-temporal cortices and cingulate cortex [1113]. In addition to the neuroimaging study, evidence of co-aggregation of bipolar disorders and schizophrenia in families [14,15] and sharing of the susceptibility genes [16,17] have stimulated an argument about the continuity between the two psychiatric disorders [18,19,20]. Accumulating evidence has supported the division of the bipolar disorders
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