Undetermined predominant polarity in a cohort of bipolar disorder patients: Prevalent, severe, and overlooked

Objectives: Predominant polarity (PP) is a concept used to define patients with bipolar disorder (BD) as presenting a tendency to manifest depressive (DPP) or manic (MPP) episodes. Still, the high percentage of patients with an undetermined PP (UPP), has been overlooked in most studies. Thus, we aimed to study UPP and outline its socio-demographic, clinical, and treatment-related features. Methods: Patients were recruited from a BD specialized unit. The sample was divided into three groups according to PP and socio-demographic and clinical variables were compared. Significant variables at univariate comparisons were included in multivariate logistic regression with UPP as the dependent variable. Results: A total of 708 BD patients were included, of which 437 with UPP (61.7%). UPP was associated with a higher number of affective relapses, when compared with DPP or MPP (chi(2)= 28.704, p<0.001). Mixed episodes (OR=1.398; CI=1.118-1.749), aggressive behaviour (OR=1.861; CI=1.190-2.913), seasonality (OR=2.025; CI= 1.289-3.501) and treatment with lamotrigine (OR= 2.101; CI=1.244-3.550) were significantly associated with UPP at the logistic regression. Limitations: Recall bias may have occurred due to mixed episode diagnostic criteria change over the years. No data on the patients' follow-up has been reported on predominant polarity changes. Conclusions: UPP is associated with a higher number of relapses, and different clinical variables related to a severe course of illness. Considering PP in patients with BD may guide the choice for differential treatment approaches having an impact on BD course of illness and patients' prognosis and recovery.