[Epidemiology of the bipolar spectrum]

The majority of epidemiologic studies indicate a prevalence rate of bipolar disorder of between 0 to 1.6% in the population. Some studies using other instruments have suggested lifetime prevalence rates of between 3 and 6.5%. Higher rates are often obtained when a wider range of cases belonging to the bipolar spectrum are included in data, for instance, cyclothymia or atypical bipolar illness. The Zurich cohort community study reported a prevalence rate of 5.5% for bipolar disorder and, moreover, found evidence for the existence of "brief hypomania", a condition characterized by short episodes of 1-3 days duration and a high recurrence. The prevalence rate found for this group was 2.2%, and is as such comparable in validity to DSM IV hypomania or mania measured by family history of depression, history of suicide attempts and treatment of depression. The quality of life for brief hypomanics is starkly reduced.