Impact of predominant polarity on long-term outcome in bipolar disorder: A 7-year longitudinal cohort study

Recent studies suggest that Predominant Polarity (PP) may be an important specifier of Bipolar Disorder (BD), establishing distinct groups of patients and providing a potential tool for tailored treatment. PP has been associated to various clinical variables present in the course of the disorder, including deficits in cognitive functioning, suicide attempts, hospitalizations and response to pharmacological treatment. However, most published studies are retrospective and cross-sectional, frequently relying on patients´ ability to recall past information, which may often be inaccurate.

Participants were recruited from the outpatient clinic of the Bipolar Disorder Research Program at the Institute of Psychiatry of the University of São Paulo. Baseline clinical and demographic variables were collected using a semi-structured questionnaire and the SCID-CV. Longitudinal data were collected through medical records, mood charts, and mood symptom scales conducted throughout a 7-year follow-up period.

Manic Predominant Polarity (MPP) was associated with a significantly higher number of hospitalizations, suicide attempts, and episodes with psychotic symptoms throughout the 7-year observed period in comparison to Depressive Predominant Polarity (DPP) and Indefinite Predominant Polarity (IPP) patients. Moreover, baseline PP was significantly associated with 7-year PP, with 67% of patients maintaining their PP both at baseline and after the 7-year follow-up period.

The present study is limited due to the statistically small sample size, although, to our knowledge, it is the largest longitudinal study conducted in this topic, and the unequally distributed frequency of patients´ visitations, which may have created intervals of unobserved periods within the follow-up period.

The results revealed PP to be an important specifier for predicting the course of the disorder. Overall, MPP was significantly associated with variables indicative of a worse outcome, suggesting that greater attention to preventive treatment should be addressed to this subgroup. Lastly, baseline PP was significantly associated with 7-year observed PP, suggesting that patients tend to remain within the same PP throughout the course of the disorder.