Mood instability metrics to stratify individuals and measure outcomes in bipolar disorder

Clinical care for bipolar disorder (BD) has a narrow focus on prevention and remission of episodes with pre-/posttreatment reductions in symptom severity as the ‘gold standard’ for outcomes in clinical trials and measurement-based care strategies. Here the study aim was to provide an innovative method for measuring outcomes in BD that has clinical utility and can stratify individuals with BD based on mood instability. The 603 participants comprised those with a BD (n = 385), other or nonaffective disorder (n = 71) or no psychiatric history (n = 147) enrolled in an longitudinal cohort for at least 10 years that collects patient-reported outcome measures (PROMs) assessing depression, (hypo)mania, anxiety and functioning every 2 months. Mood instability was calculated as the intraindividual s.d. of PROMs over 1-year rolling windows and stratified into low, moderate and high thresholds. Individuals with BD had significantly higher 1-year rolling s.d. for depression, (hypo)mania and anxiety compared with psychiatric comparisons (small–moderate effects) and healthy controls (large effects). A significantly greater proportion of scores for those with BD fell into the moderate (depression 50.6%; anxiety 36.5%; and (hypo)mania 52.1%) and high thresholds (depression 9.4%; anxiety 6.1%; and (hypo)mania 10.1%) compared with psychiatric comparisons (moderate 32.3–42.9% and high 2.6–6.6%) and healthy controls (moderate 11.5–31.7% and high 0.4–5.8%). Being in the high or moderate threshold predicted worse mental health functioning (small to large effects). Mood instability, as measured in commonly used PROMs, characterized the course of illness over time, correlated with functional outcomes and significantly differentiated those with BD from healthy controls and psychiatric comparisons. The results suggest a paradigm shift in monitoring outcomes in BD, by measuring intraindividual s.d. as a primary outcome index. This study introduces a method to measure outcomes in bipolar disorder by quantifying mood instability over time.