Reassessing the bipolar-unipolar dichotomy.

This paper is a critical review of the literature on the dichotomous classification of affective disorders into unipolar and bipolar types. The majority of genetic studies show significant overlap in the liability to develop two forms of illness, and the majority of lithium studies show a similar clinical responsiveness of both groups to both acute and maintenance treatment. Biological studies comparing the two groups are difficult to interpret as most have compared manics to depressives without controlling for motor activity, excitement, and other state-dependent clinical variables. Viewed in light of our research findings in a recent genetic study of affective states, we believe these data suggest that the separation of affective disorders by polarity may have been premature, and that the search for heterogeneity should now be carried out using alternative strategies.