The Prevalence and Diagnostic Validity of Short-Duration Hypomanic Episodes and Major Depressive Episodes.

Current diagnostic criteria for a hypomanic episode, as outlined in both the fourth and fifth editions of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV and DSM-5), require a minimum duration of four consecutive days of symptoms of mood elevation. The 4-day criterion for duration of hypomania has been challenged as arbitrary and lacking empirical support, with many arguing that shorter-duration hypomanic episodes are highly prevalent and that those experiencing these episodes are clinically more similar to patients with bipolar disorder than to those with unipolar major depressive disorder. We review the current evidence regarding the prevalence, diagnostic validity, and longitudinal illness correlates of shorter-duration hypomanic episodes and summarize the arguments for and against broadening the diagnostic criteria for hypomania to include shorter-duration variants. Accumulating findings suggest that patients with major depressive episodes and shorter-duration hypomanic episodes represent a complex clinical phenotype, perhaps best conceptualized as being on the continuum between those with unipolar depressive episodes alone and those with DSM-5-defined bipolar II disorder. Further investigation is warranted, ideally involving large prospective, controlled studies, to elucidate the diagnostic and treatment implications of depression with shorter-duration hypomanic episodes.