Bipolar II disorder: arguments for and against a distinct diagnostic entity.

OBJECTIVE: As a commitment to the International Society for Bipolar Disorders (ISBD), a Task Force was developed to investigate the diagnostic value of bipolar II disorder.
METHODS: Task Force members worked jointly reviewing all relevant literature (original articles, reviews, letters, book chapters and congress presentations) that included 'bipolar II disorder' and/or 'hypomania' as key words.
RESULTS: Bipolar II disorder appears to be a reasonably valid and reliable diagnostic category yet often underdiagnosed or misdiagnosed as unipolar disorder or personality disorder. Moreover, it is officially recognized as a mental disorder in DSM-IV-TR but not in ICD-10, and many clinicians still regard it as a milder form of manic-depressive illness, despite data supporting high morbidity and mortality rates. In fact, bipolar II may be the most prevalent bipolar phenotype, although current diagnostic boundaries are seen as quite restrictive concerning the required duration for hypomania (4 days), the exclusion of hypomanic episodes potentially triggered by antidepressants and other substances, and the negligence of hypomanic mixed states. The course of bipolar II disorder is characterized by depressive predominant polarity, and its treatment is still controversial and poorly evidence-based.
CONCLUSIONS: Bipolar II disorder is supported as a distinct category within mood disorders, but the definition and boundaries deserve a greater clarification in the DSM-V and ICD-11.