The essential feature of Bipolar II Disorder is a clinical course that is characterized by the occurrence of one or more Major Depressive Episodes (Criterion A) accompanied by at least one Hypomanic Episode (Criterion B). Hypomanic Episodes should not be confused with the several days of euthymia that may follow remission of a Major Depressive Episode. The presence of a Manic or Mixed Episode precludes the diagnosis of Bipolar II Disorder (Criterion C). Episodes of Substance-Induced Mood Disorder (due to the direct physiological effects of a medication, other somatic treatments for depression, drugs of abuse, or toxin exposure) or of Mood Disorder Due to a General Medical Condition do not count toward a diagnosis of Bipolar II Disorder. In addition, the episodes must not be better accounted for by Schizoaffective Disorder and are not superimposed on Schizophrenia, Schizophreniform Disorder, Delusional Disorder, or Psychotic Disorder Not Otherwise Specified (Criterion D). The symptoms must cause clinically significant distress or impairment in social, occupational, or other important areas of functioning (Criterion E). In some cases, the Hypomanic Episodes themselves do not cause impairment. Instead, the impairment may result from the Major Depressive Episodes or from a chronic pattern of unpredictable mood episodes and fluctuating unreliable interpersonal or occupational functioning.
Individuals with Bipolar II Disorder may not view the Hypomanic Episodes as pathological, although others may be troubled by the individual’s erratic behavior. Often individuals, particularly when in the midst of a Major Depressive Episode, do not recall periods of hypomania without reminders from close friends or relatives. Information from other informants is often critical in establishing the diagnosis of Bipolar II Disorder.