Background: Sub-syndromal symptoms in bipolar disorder impair functioning and diminish quality of life.
Aims: To examine factors associated with time spent with sub-syndromal symptoms and to characterise how these symptoms influence outcomes.
Method: In a double-blind randomised maintenance trial, patients received either olanzapine or lithium monotherapy for 1 year. Stepwise logistic regression models were used to identify factors that were significant predictors of percentage time spent with sub-syndromal symptoms. The presence of sub-syndromal symptoms during the first 8 weeks was examined as a predictor of subsequent relapse.
Results: Presence of sub-syndromal depressive symptoms during the first 8 weeks significantly increased the likelihood of depressive relapse (relative risk 4.67, P<0.001). Patients with psychotic features and those with a greater number of previous depressive episodes were more likely to experience sub-syndromal depressive symptoms (RR=2.51, P<0.001 and RR=2.35, P=0.03 respectively).
Conclusions: These findings help to identify patients at increased risk of affective relapse and suggest that appropriate therapeutic interventions should be considered even when syndromal-level symptoms are absent.