Are there two types of unipolar depression?

Personality traits and clinical characteristics in psychiatric outpatients with affective disorder were examined. Two groups of unipolar patients, divided on the basis of treatment response to tricyclic antidepressants, were compared to a bipolar group. While the unipolar-T (tricyclic responder) group showed premorbid personality traits of chronic anxiety and obsessiveness, neither the bipolar nor unipolar-L (tricyclic nonresponder, lithium carbonate responder) groups showed such findings. In fact, the unipolar-L and bipolar groups were similar not only with regard to personality variables, but also in terms of both drug response and certain family history features. These findings cast doubt on the homogeneity of unipolar depression and suggest the possibility of a subtype of unipolar depression with psychobiologic and personality features resembling bipolar disorder.