Abstract
Among subjects with bipolar disorder (BD), depression is much more prevalent (1, 2) and has stronger effects on mortality and psychosocial impairment than mania or hypomania (3, 4). Recently, the clinical, biological, and treatment characteristics of major depressive episodes (MDE) in BD as compared to major depressive disorder (MDD) have been a focus of attention for researchers and clinicians (5–21). However, specific clinical or biological markers for bipolar depression are still lacking. In current diagnostic systems, the same diagnostic criteria apply to MDE occurring during MDD or during the course of BD (22).