Is 4 days the minimum duration of hypomania in bipolar II disorder?

DSM-IV requires that bipolar II disorder has hypomania with a minimum duration of 4 days, a cutoff not based on data. The study aim was to test if hypomania lasting 2 to 3 days could identify a group of bipolar II with typical clinical features of bipolar disorders. Consecutively, 65 unipolar and 103 bipolar II major depressive episode (MDE) outpatients were interviewed with the Structured Clinical Interview for DSM-IV. Almost all had had 2 to 3 days of hypomania, and all had had more than one hypomania. Typical clinical variables distinguishing bipolar from unipolar disorders (age at onset, atypical features, and recurrences) were compared. Bipolar II had significantly lower age at onset, more recurrences, and more atypical features. Findings suggest that hypomania lasting 2 to 3 days may identify a bipolar II group having typical features of bipolar disorders.