Bipolar Disorder: Open Access
Open Access

Abstract

A Reduced Gray Matter Volume in Patients with Bipolar II Disorder in a Japanese Sample: A Comparison with Schizophrenia

Akeo Kurumaji, Michio Itasaka, Akihito Uezato, Kazuo Takiguchi, Daisuke Jitoku, Mizue Hobo and Kiyotaka Nemoto

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.