Mood instability as a predictor of clinical and functional outcomes in adolescents with bipolar I and bipolar II disorder

Background: Traditional assessment and treatment of bipolar disorder (BD) often overlooks an important feature of the illness, mood instability (MI). MI - the presence of intense, rapidly shifting emotional states - is associated with a number of poor prognostic outcomes. This study examined whether MI among adolescents with BD was cross-sectionally related to bipolar subtype (I vs. II) and prognostically associated with symptoms and functioning over 3 months. Methods: Participants included 145 adolescents (mean age: 15.6 years +/- 1.4) with BD I or II with a mood episode in the previous 3 months. Depression and (hypo) mania instability were computed using the root mean square successive difference (rMSSD) score, reflecting both the size and temporal order of changes in weekly depression and (hypo) mania scores (over 12 weeks) from the Adolescent Longitudinal Interval Follow-Up Evaluation. Results: Greater depression instability was associated with BD II, whereas greater (hypo) mania instability was associated with BD I. Baseline MI, particularly depression, predicted more instability, a higher percentage of weeks in a clinical mood state, and poorer global functioning over 3 months, even when covarying concurrent mood severity scores. Limitations: The clinical measure of symptoms used retrospective reports of clinically significant symptoms only. We were unable to standardize medication use or adherence. Conclusions: MI differs by diagnostic subtype, is relatively stable over time, and predicts clinical and functional outcomes. Targeting MI should be considered a clinical focus to augment traditional methods of assessing and treating BD during adolescence to enhance clinical and functional outcomes.