Kraepelin's broad concept of manic-depressive illness was challenged in the 1960s by several European and American investigators. This led to the unipolar-bipolar distinction, with considerable restriction of the boundaries of bipolar disorder in favor of unipolar depressions. This concept has now been implicity adopted by official systems of classification worldwide. This review summarizes recent research data that suggest that a partial return to Kraepelin's broad concept of manic-depressive illness is in order. In reassessing the unipolar-bipolar dichotomy, the authors propose that the classification of depressions should incorporate such nonsymptomatologic considerations as family history, temperament, abruptness of onset, recurrence (periodicity and seasonality), and Pharmacologie response.

Depending on the definitions used, the unipolar-bipolar ratio has ranged from 10:1 to 4:1. Recent American and European investigations, including studies by the authors and their Italian collaborators, suggest that this ratio may be closer to 2:1 and even as low as 1:1. This conclusion is further supported by genetic data, prospective follow-up studies, pharmacologie response, and examination of interepisodic temperaments. Thus, many depressives with premorbid or intermorbid hyperthymie, irritable or cyclothymie temperaments can now be classified as bipolar. Variously referred to as pseudo-unipolar, unipolar II, bipolar III, bipolar II, or the “ soft” bipolar speetrum, these depressive conditions present diagnostic and therapeutic challenges to the clinician. Special subgroups may be at risk for rapid cycling when overexposed to tricyclic antidepressants. Finally, a significant minority of soft bipolars uppear to be prominent in leadership positions and artistic domains.