Bipolar Disorder

Epidemiology

Although the rates may vary slightly, a number of epidemiologic studies conducted world wide have established that the lifetime prevalence of bipolar disorder is approximately 1% (Bland, 1997; Maj et al, 2002). The prevalence of bipolar disorder is similar in males and females and there appears to be no difference in prevalence rates between different racial groups (Bland, 1997; Montgomery & Cassano, 1996). The time of onset is often in the adolescencent years or young adult life; with depressive episodes usually proceeding the onset of the first manic episode (Akiskal et al, 2000; Bland, 1997; Robb, 1999).

There are two distinct forms of bipolar disorder, which differ in their epidemiology. Bipolar I disorder is an illness characterised by manic and depressive episodes – this is the ‘classic’ form of the disorder. Bipolar II disorder is an illness characterised by hypomania (a less severe form of mania) and depressive episodes. Bipolar I disorder is equally common in women and men, while Bipolar II disorder is more common in women than in men (Montgomery & Cassano, 1996). There is some evidence that women with bipolar disorder may be more prone than men to depressive episodes (Montgomery & Cassano, 1996).

Prevalence of Bipolar I and II disorders, as reported by the Epidemiologic Catchment Area Study (ECA) and the National Comorbidity Study (NCS) (U.S. Department of Health and Human Services, 1999)

The peak age of onset of the first symptoms of bipolar disorder is between 15 and 19 years of age, with a median age of onset of 18 years. Bipolar disorder can present before puberty, but this is rare and can be difficult to distinguish from other severe psychiatric disorders such as schizophrenia (Torrey, 1999). Elderly patients can also present with symptoms of bipolar disorder for the first time in old age. However, manic and depressive symptoms in this age group have usually been present for many years and in mild cases may have often gone untreated. Onset of bipolar disorder in the elderly is usually associated with central nervous system injury, such as stroke (Marnevos & Angst, 2000; Shulman & Tohen, 1994).