Bipolar II Disorder may be more common in women than in men. Gender appears to be related to the number and type of Hypomanic and Major Depressive Episodes. In men the number of Hypomanic Episodes equals or exceeds the number of Major Depressive Episodes, whereas in women Major Depressive Episodes predominate. In addition, Rapid Cycling is more common in women than in men. Some evidence suggests that mixed or depressive symptoms during Hypomanic Episodes may be more common in women as well, although not all studies are in agreement. Thus, women may be at particular risk for depressive or intermixed mood symptoms. Women with Bipolar II Disorder may be at increased risk of developing subsequent episodes in the immediate postpartum period.
Community studies suggest a lifetime prevalence of Bipolar II Disorder of approximately 0.5%.
Roughly 60%-70% of the Hypomanic Episodes in Bipolar II Disorder occur immediately before or after a Major Depressive Episode. Hypomanic Episodes often precede or follow the Major Depressive Episodes in a characteristic pattern for a particular person. The number of lifetime episodes (both Hypomanic Episodes and Major Depressive Episodes) tends to be higher for Bipolar II Disorder compared with Major Depressive Disorder, Recurrent. The interval between episodes tends to decrease as the individual ages. Approximately 5%-15% of individuals with Bipolar II Disorder have multiple (four or more) mood episodes (Hypomanic or Major Depressive) that occur within a given year. If this pattern is present, it is noted by the specifier With Rapid Cycling (see page 427). A rapid-cycling pattern is associated with a poorer prognosis.
Although the majority of individuals with Bipolar II Disorder return to a fully functional level between episodes, approximately 15% continue to display mood lability and interpersonal or occupational difficulties. Psychotic symptoms do not occur in Hypomanic Episodes, and they appear to be less frequent in the Major Depressive Episodes in Bipolar II Disorder than is the case for Bipolar I Disorder. Some evidence is consistent with the notion that marked changes in sleep-wake schedule such as occur during time zone changes or sleep deprivation may precipitate or exacerbate Hypomanic or Major Depressive Episodes. If a Manic or Mixed Episode develops in the course of Bipolar II Disorder, the diagnosis is changed to Bipolar I Disorder. Over 5 years, about 5%-15% of individuals with Bipolar II Disorder will develop a Manic Episode.