Approximately 5%—15% of individuals with bipolar II disorder have multiple (four or more) mood episodes (hypomanic or major depressive) within the previous 12 months. If this pattern is present, it is noted by the specifier ”with rapid cycling.” By definition, psy- chotic symptoms do not occur in hypomanic episodes, and they appear to be less frequent in the major depressive episodes in bipolar II disorder than in those of bipolar I disorder.
Switching from a depressive episode to a manic or hypomanic episode (with or with- out mixed features) may occur, both spontaneously and during treatment for depression.
About 5%—15% of individuals with bipolar II disorder will ultimately develop a manic ep- isode, which changes the diagnosis to bipolar I disorder, regardless of subsequent course.
Making the diagnosis in children is often a challenge, especially in those with irritabil— ity and hyperarousal that is nonepisodic (i.e., lacks the well-demarcated periods of altered mood). Nonepisodic irritability in youth is associated with an elevated risk for anxiety dis- orders and major depressive disorder, but not bipolar disorder, in adulthood. Persistently irritable youths have lower familial rates of bipolar disorder than do youths who have bi- polar disorder. For a hypomanic episode to be diagnosed, the child’s symptoms must ex- ceed what is expected in a given environment and culture for the child’s developmental stage. Compared with adult onset of bipolar II disorder, childhood or adolescent onset of the disorder may be associated with a more severe lifetime course. The 3-year incidence rate of first-onset bipolar II disorder in adults older than 60 years is 0.34%. However, dis— tinguishing individuals older than 60 years with bipolar II disorder by late versus early age at onset does not appear to have any clinical utility.
Genetic and physiological. The risk of bipolar II disorder tends to be highest among rel- atives of individuals with bipolar II disorder, as opposed to individuals with bipolar I dis- order or major depressive disorder. There may be genetic factors inﬂuencing the age at onset for bipolar disorders.
Course modifiers. A rapid-cycling pattern is associated with a poorer prognosis. Return to previous level of social function for individuals with bipolar II disorder is more likely for individuals of younger age and with less severe depression, suggesting adverse effects of prolonged illness on recovery. More education, fewer years of illness, and being mar- ried are independently associated with functional recovery in individuals with bipolar disorder, even after diagnostic type (I vs. II), current depressive symptoms, and presence of psychiatric comorbidity are taken into account.
Whereas the gender ratio for bipolar I disorder is equal, findings on gender differences in bipolar II disorder are mixed, differing by type of sample (i.e., registry, community, or clinical) and country of origin. There is little to no evidence of bipolar gender differences, whereas some, but not all, clinical samples suggest that bipolar II disorder is more com- mon in females than in males, which may reﬂect gender differences in treatment seeking or other factors.
Patterns of illness and comorbidity, however, seem to differ by gender, with females being more likely than males to report hypomania with mixed depressive features and a rapid-cycling course. Childbirth may be a specific trigger for a hypomanic episode, which can occur in 10%—20% of females in nonclinical populations and most typically in the early postpartum period. Distinguishing hypomania from the elated mood and reduced sleep that normally accompany the birth of a child may be challenging. Postpartum hypomania may foreshadow the onset of a depression that occurs in about half of females who expe- rience postpartum ”highs.” Accurate detection of bipolar II disorder may help in estab- lishing appropriate treatment of the depression, which may reduce the risk of suicide and infanticide.