Clinical differences between bipolar II depression and unipolar major depressive disorder: lack of an effect of age

Background: Inconsistent clinical differences were reported in bipolar II versus unipolar depression. Age difference may be a confounding factor. Study aims were to describe the clinical and family history features of bipolar II versus unipolar depression, and to control for the possible counfounding effect of age on clinical features. Methods: Consecutive 126 unipolar and 187 bipolar II major depressive episode (MDE) outpatients were interviewed with the Structured Clinical Interview for DSM-IV. Variables studied were gender, age, age of onset, MDE recurrences, axis I comorbidity, MDE severity, psychotic, melancholic, and atypical features, depression chronicity, melancholic, atypical, and hypomanic symptoms, depressive mixed state-DMX3 (MDE+three or more concurrent hypomanic symptoms), and mood disorders family history. The effect of age on clinical differences was controlled by logistic regression (by adding age as an independent variable after each independent variable). Results: Bipolar II had significantly lower age, lower age of onset, more recurrences, more atypical features, more DMX3, more family history of bipolar II and MDE. Almost all the clinical differences found significant in the first analysis resulted still significant when controlled for age. Limitations: Single interviewer, non-blind, cross-sectional assessment, bipolar II diagnosis based on history. Conclusions: Results confirmed previous findings, and showed that bipolar II—unipolar MDE clinical differences were not related to age.