Similarities of Aspects of Biological Rhythms between Major Depression and Bipolar II Disorder Compared to Bipolar I Disorder: A Finding from the Early-Onset Mood Disorder Cohort

Objective The biological rhythm is closely related to mood symptoms. The purpose of this study was to assess the differences in biological rhythms among subjects with mood disorder [bipolar I disorder (BD I), bipolar II disorder (BD II), major depressive disorder (MDD)] and healthy control subjects. Methods A total of 462 early-onset mood disorder subjects were recruited from nine hospitals. The controls subjects were recruited from the general population of South Korea. Subject groups and control subject were evaluated for the Korean language version of Biological Rhythms Interview of Assessment in Neuropsychiatry (K-BRIAN) at the initial evaluation. Results The mean K-BRIAN scores were 35.59 [standard deviation (SD)=13.37] for BD I, 43.05 (SD=11.85) for BD II, 43.55 (SD=12.22) for MDD, and 29.1 (SD=8.15) for the control group. In the case of mood disorders, biological rhythm disturbances were greater than that in the control group (p<0.05). A significant difference existed between BD I and BD II (BD I<BD II, p<0.001) and between BD I and MDD (BD I<MDD, p< 0.001) but no difference was observed between BD II and MDD. Conclusion BD II and MDD are similar to each other but different from BD I in biological rhythm patterns in early-onset mood disorder cases. Biological rhythm disturbances are similar for early-onset major depression and BD II.