Bipolar Disorder II is less well understood than BP I, even though the rate of prevalence in the wider population seems to be about equal. Previously considered a “lesser form” of bipolar, doctors note that rates of illness severity and suicide risk are very comparable in the two forms of bipolar. Less research has been done on BP II, with studies often failing to distinguish between participants with BP I and BP II, and considering their treatment to be the same.
BD II diagnosis requires at least one lifetime hypomanic episode and one major depressive episode. Despite clarity of BD II diagnostic criteria, clinicians struggle to accurately identify it in practice. BD II is often either missed or incorrectly diagnosed, resulting in an over 10-year delay in diagnosis. Often, BD II is misdiagnosed as major depressive disorder, perhaps partly because patients may not identify the hypomanic state as in any way abnormal.
Disease burden and suicide risk
BD II was previously—and incorrectly—labeled a “less severe” version of BD I. In fact, studies consistently show comparable disease burden in BD I and II. A recent Swedish study reported higher rates of depressive episodes, illness onset at a younger age, and significantly higher rates of psychiatric comorbidity (anxiety disorders, eating disorders, and ADHD) among patients with BD II compared with those with BD I.
Suicide is a significant risk for all patients with BD, and historically patients with BD I were viewed as having a higher risk than BD II due to the extremities of mania. However, data from a number of sources support that suicide risk is high across all patients with BD, and relatively little difference is found in risk for patients with BD I versus BD II.
Treatments have often been assumed to be the same for BP I and BP II, even though some studies show limited results of differential response to treatment between the two. One treatment that has been studied with a randomized control trial is interpersonal and social rhythm therapy (IPSRT), which we have looked at before in MoodSurfing.
A neglected condition, BD II causes unnecessary suffering in those who are misdiagnosed or for whom appropriate treatments are unclear. More research is urgently needed to improve identification and treatments for BD II.