Relationships between recurrence and polarity in major depressive disorders: Pooled analysis of the BRIDGE and BRIDGE-II-MIX cohorts.

Background: current classifications of mood disorders focus on polarity rather than recurrence, separating bipolar disorder from major depressive disorder (MDD). The aim of the present study is to explore the possible relationships between number and frequency of depressive episodes and clinical variables associated to bipolarity, in a large sample of MDD patients.

Methods: the clinical characteristics of 7055 patients with MDD were analyzed and compared according to the number and frequency of depressive episodes. Two stepwise backward logistic regression model were used to identify the predictive value of clinical features based on the presence of high number (≥3 episodes) and high frequency (≥3 episodes/year) of depressive episodes.

Results: high-recurrence and high-frequency MDD patients showed greater family history for bipolar disorder, higher prevalence of psychotic features, more suicide attempts, higher rates of treatment resistance and mood switches with antidepressants (ADs) and higher rates of bipolarity diagnosis according to Angst criteria, compared to low-recurrence and low-frequency patients. Logistic regressions showed that a brief current depressive episode, a previous history of treatment resistance and AD-induced mood switches, a diagnosis of bipolarity and comorbid borderline personality disorder were the variables associated with both high-recurrence and high-frequency depression.

Limitations: the study participating centers were not randomly selected and several variables were retrospectively assessed.

Conclusions: even in the absence of hypomanic/manic episodes, high-recurrence and high-frequency MDD seem to be in continuity with the bipolar spectrum disorders in terms of clinical features and, perhaps, treatment response.