Background: DSM-IV 4-day minimum hypomania duration is not evidence-based. Epidemiologic data suggest that briefer hypomanias are prevalent in the community. We sought to find out the relative prevalence of short (2-3 days) versus long (>/=4 days) hypomanias in private practice.
Methods: 206 bipolar-II (BP-II) depressed outpatients (group B) and a group of 140 remitted BP-II (group R) were assessed with the DSM-IV Structured Clinical Interview, as modified by the authors. BP-II with short vs. longer hypomania were compared on such bipolar validators as early age at onset, depressive recurrence, atypical feature specifier, depressive mixed state and bipolar family history. In addition, to ascertain the bipolar status of depressed patients with brief hypomanias, we included a comparison group of 178 major depressive disorder (MDD) patients assessed when depressed.
Results: 27-30% of hypomanias (depending on whether assessment occurred when patients were depressed or in remission) had 2-3-day duration; 72% lasted less than 4 weeks. Except for the atypical feature specifier, BP-II with short vs. BP-II with longer hypomania were not significantly different on bipolar validators. Moreover, BP-II with short, like its longer hypomanic counterpart, was significantly different from the comparison MDD group on all bipolar indicators.
Limitations: Single interviewer and retrospective evaluation of duration of hypomania.
Conclusions: As BP-II patients almost never present clinically in a hypomanic episode, the retrospective assessment of the duration of these episodes is clinically unavoidable. Most hypomanias last from 2 days to a few weeks. BP-II with shorter vs. longer hypomanias had significantly higher rates of females, comorbidity and atypical features, but were otherwise indistinguishable on crucial bipolar validators. Furthermore, such validators, including bipolar family history, robustly distinguished BP-II with short hypomanias from the MDD group. The conservative 4-day threshold would misclassify one out of three BP-II as MDD. Such misclassification has relevant implications for treatment and outcome, as well as clinical research methodology for depressive and bipolar disorders.