Redefining Bipolar Disorder

Editor, Primary Psychiatry and Psychiatry Weekly, Professor of Psychiatry, New York University School of Medicine

Prevalence of BPD

The lack of biological measure limits the degree of certainty present in the process of making a psychiatric diagnosis. Nowhere is this limitation more evident than in trying to define bipolar disorder (BPD). Based on existing criteria, estimates of the lifetime prevalence of BPD range from 0.8% for BP-I to 1.1% for BP-II. However, it has long been argued that bipolar spectrum disorder may in fact be much more common—affecting about 6% of the population. It is argued that existing diagnostic criteria for BPD are set too high, that is, they are too restrictive in terms of symptom severity, and thus lead to underestimation of prevalence in epidemiologic studies, and underrecognition and under treatment in the clinical setting.

NCS-R Data

Newly published data from the National Comorbidity Survey Replication (NCS-R) provides new evidence that patients with bipolar illness are in fact being under diagnosed, and as a consequence, are being treated inappropriately. The NCS-R is a survey of nearly 10,000 adults age 18 or older. The major finding of the latest analysis is that mania patients do not meet existing diagnostic criteria for BPD, yet have a chronic course and clinically significant impairment. Although this group is described as having “subthreshold bipolar disorder,” in the view of the authors, this reflects outdated diagnostic criteria. At the moment, many patients with subthreshold bipolar disorder are diagnosed as bipolar disorder not otherwise specified (BD-NOS), because they do not meet strict criteria for any specific type of bipolar disorder noted in the Diagnostic and Statistical Manual for Mental Disorders.

According to the authors, this study “demonstrates the validity of the spectrum concept of bipolarity.” It appears that BPD is often misdiagnosed among younger adults because the disorder evolves over time. Early in its course, it may be very hard to distinguish from unipolar depression. This is one reason why it is important to take a careful family history and to ask very specifically about any past episodes that might represent mild hypomania.

Comorbidity

Patients with BPD are in most cases being treated, but they are likely to be treated for a comorbid condition, or for unipolar depression. The study found that over the course of a year, only 9% of patients with bipolar spectrum disorder received appropriate medication in the general medical setting. In the psychiatric setting, 45% received appropriate treatment. With respect to comorbidity, the NCS-R found pervasive comorbidity across the bipolar spectrum, with 88.4% of subthreshold bipolar, and 97.7% of threshold cases having at least one other psychiatric disorder. Frequent comorbid conditions were substance abuse, panic disorder, and obsessive-compulsive disorder. The authors speculate “this pervasive comorbidity across the BPD spectrum is suggestive of disturbances in multiple regulatory systems and should be a topic for future research.”

Reference

Merikangas KR, Akiskal HS, Angst J, et al. Lifetime and 12-month prevalence of bipolar spectrum disorder in the National Comorbidity Survey Replication. Arch Gen Psychiatry. 2007;64:543-552.

Disclosure: Dr. Sussman has received honoraria from AstraZeneca, Bristol-Myers Squibb, and GlaxoSmithKline.