The symptom structure of bipolar acute episodes: in search for the mixing link.

Objective: The nature of mixed mood episodes is still a matter of controversy amongst experts. Currently, the approach to this syndrome is mainly categorical and very restrictive. The factor-structure of bipolar mood episodes has not been studied yet. We performed a dimensional analysis of the structure of bipolar episodes aimed at identifying a factor deconstructing mixed episodes; furthermore, we analyzed correlations of factors emerging from the factorial analysis of the Brief Psychiatric Rating Scale (BPRS) with Temperament Evaluation of Memphis-Pisa-Paris-San Diego (TEMPS-A) and predominant polarity.

Method: 187 consecutive bipolar I inpatients hospitalized for DSM-IV-TR acute mood episodes (depressive, manic or mixed) underwent a standardized assessment, including the 24-item Brief Psychiatric Rating Scale (BPRS 4.0), the 21-item Hamilton Depression Rating Scale (HDRS-21), the Young Mania Rating Scale (YMRS) and the TEMPS-A. Principal factor analysis was performed on BPRS-24 items.

Results: This analysis revealed five factors corresponding to "psychosis", "euphoric mania", "mixity", "dysphoria" and "inhibited depression", capturing 71.89% of the rotated variance. The mixity factor was characterized by higher rates of suicidal ideation, more mixed episodes, higher frequencies of antidepressant (AD) use, depressive predominant polarity and anxious temperament.

Discussion: The factor-structure of the BPRS in inpatients with bipolar I disorder with an acute episode of any type is pentafactorial; one factor identified is the mixity factor, which is independent from other factors and characterized by anxiety and motor hyperactivity and by the absence of motor retardation. Our results should prompt reconsideration of proposals for DSM-5 diagnostic criteria for the mixed features specifier. Limitations of the study include the relative small sample, the absence of drug-naïve patients and the use of rating scales no specific for mixed states.