Clinical course of the bipolar II disorder in a Japanese sample

The bipolar II disorder has been recognized a mental disorder distinctive from the bipolar I disorder, showing the stability of diagnosis in prospective studies. However, the characterization of the bipolar II disorder still remains under investigation.

The present study was conducted on consecutively admitted bipolar II inpatients diagnosed by DSM-IV-TR to delineate the clinical features.

The types of initial mood disorders of the bipolar II inpatients were divided into four groups, i.e., major depressive episode (MDE), hypomanic episode (HME), and dysthymic and cyclothymic disorders. Seventy-one percent of all the patients belonged to the MDE group, a half of which underwent the first HME following the first MDE. The number of patients that exhibited the HME within one year after the first MDE was the highest in a widely distributed interval of years between the first MDE and the first HME. The cyclothymic disorder group was relatively young at the onset and was more prone to attempt suicide. Moreover, there might be a complex connection with other psychiatric disorders, such as anxiety disorders, in the longitudinal course of the bipolar disorder.

The present study was carried out on a limited number of patients admitted to one hospital. The data are partly based on the retrospective information from the patients and their relatives. The generalization of the results requires further studies.

The bipolar II disorder could be divided into heterogeneous groups in the longitudinal course. Hence, paying attention to the heterogeneity in clinical practice and a study of the disorder are required.