Episodic density, subsyndromic symptoms, and mood instability in late-life bipolar disorders: A 5-year follow-up study.

Objectives: Characterization of clinical course in old age bipolar disorder (OABD) is scarce and based solely on episode density (ED). The aim of this study was to explore mood instability (MI) and subsyndromal symptomatology (SS) in a prospective cohort of OABD. Further, we contrasted these measures with a cohort of young age bipolar disorder (YABD).

Methods: Life charts from weekly mood ratings were used to compute the number of weeks spent with subsyndromal symptoms (SD), the ED, and the MI during follow-up for a cohort of OABD (N = 38) that excluded late onset BD. Linear and logistic regression models were fitted to compare the clinical course of OABD with a cohort of YABD (N = 52) and to explore the relationship between these measures and functional outcomes.

Results: Median follow-up was 5 years (IQR: 3.6-7.9). OABD (61.6 years, SD: 8.3) spent 15%, 6%, and 3% of their follow-up with depressive, manic, and mixed symptoms, respectively, and suffered 4.2 mood changes per year (SD: 2.6). No significant differences between OABD and YABD regarding ED or MI emerged in multivariate analysis, while a higher subsyndromal manic symptom burden was observed in OABD (β coefficient: 3.79, 95%CI: 0.4-7.2). Both SS and MI were associated with functional outcomes in OABD.

Conclusions: The course of illness throughout OABD was similar to the one observed in YABD except for a higher subsyndromal manic burden. This study extended the association of MI and SD with global functioning to the late-life BD.