Prevalence, chronicity, burden and borders of bipolar disorder

Bipolar disorder (BD) has traditionally been thought of as an episodic condition, characterized by periods of hypomania/mania and depression. However, evidence is accumulating to suggest that this condition is associated with significant chronicity. For a large proportion of patients with BD, residual, sub-syndromal symptoms persist between major syndromal episodes, and studies have shown that many patients with bipolar disorder are symptomatic for approximately 50% of the time over follow-up periods of greater than 10 years. Moreover, while the prevalence of BD has been estimated to be around 1–2%, there is growing evidence that this may be a substantial underestimation. There are a number of reasons for this potential underestimation, including difficulties in diagnosis. Adding to the burden of BD is the issue of comorbidity, with an increased prevalence of many chronic conditions in those with a primary diagnosis of BD. Conversely, for many patients with chronic conditions, both medical and psychiatric, BD frequently exists as a comorbid secondary diagnosis. This issue of comorbidity complicates estimates of use of pharmaceutical agents for BD, such as mood stabilizers, which are known to be used off-label in conditions such as borderline personality or substance use disorder. We speculate that such off-label prescribing may not be truly off-label but may be instead fully justified by an overlooked secondary diagnosis of BD. Finally, we discuss the association of bipolar disorder with a significant economic burden, to the individual and to society, both due to the direct costs of medical expenditure and indirect costs such as loss of productivity and increased mortality.