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Bipolar Disorder Underrecognized, Poorly Treated
The lifetime prevalence rate of bipolar disorder in the United States may be twice as high as previously thought when the disease is viewed as a larger spectrum disorder, according to a study from the NIMH that was published in the May Archives of General Psychiatry. In addition, researchers found that many persons with bipolar disorder are not receiving appropriate treatment.
Kathleen Merikangas, PhD, and colleagues found lifetime prevalence estimates of 1% for bipolar I disorder and 1.1% for bipolar II disorder in a sample of US adults; this supports previous findings on prevalence estimates. However, Dr. Merikangas’ group determined that an additional 2.4% of persons will develop a milder, third subtype of the disorder—bipolar–not otherwise specified (or subthreshold bipolar disorder). The investigators applied broader criteria for subthreshold bipolar disorder to characterize people who fall just below the current diagnostic thresholds for bipolar II disorder.
REDEFINING BIPOLAR DISORDER
The researchers used standard clinical rating scales to assess the severity of depressive and manic symptoms and the magnitude of role impairment associated with bipolar spectrum disorder. Indicators of clinical severity included age at onset, chronicity, symptom severity, role impairment, comorbidity, and treatment. Clinical severity and role impairment among those with threshold bipolar disorder were comparable to those of patients in clinical settings, suggesting that bipolar disorder in people selected from the general population does not differ in severity from that in patients identified in clinical settings.
“Even though severity and impairment are greater for threshold than for subthreshold bipolar disorder, subthreshold cases still have moderate to severe clinical severity and role impairment,” Dr. Merikangas and colleagues reported. “This study presents the first prevalence estimates of the bipolar disorder spectrum in a probability sample of the United States. Subthreshold bipolar disorder is common, clinically significant, and underdetected in treatment settings.”
The researchers analyzed data from the National Comorbidity Survey Replication, a questionnaire on mental disorders that was completed by 9,282 US adults ages 18 and older. Version 3.0 of the World Health Organization’s Composite International Diagnostic Interview was used to assess for DSM-IV lifetime and 12-month axis I disorders.
TREATING BIPOLAR DISORDERS
Between 89% and 95% of those with either bipolar I or bipolar II disorder received treatment, compared with 69% of those with subthreshold bipolar disorder, according to the investigators. Patients with bipolar I and bipolar II disorder were treated most frequently by a psychiatrist, while those with subthreshold bipolar disorder were treated most frequently by a general medical professional.
Dr. Merikangas’ group pointed out that although most people with bipolar disorder receive lifetime professional treatment for emotional problems, use of mood stabilizers is uncommon, especially in general medical settings. “A significantly higher proportion of patients receiving psychiatric (45%) versus general medical (9%) treatment received mood stabilizers, which have been shown to be superior to antidepressants in the treatment of bipolar disorder,” the investigators reported. “Conversely, the proportion of patients who did not receive appropriate treatment during the past 12 months was significantly greater in those who received treatment from general medical physicians (73%) versus psychiatric specialists (43%).”
The researchers also found a high magnitude of comorbidity with other mental disorders among patients with bipolar disorder. As many as 97% of patients with bipolar disorder had coexisting psychiatric conditions, including anxiety, depression, or substance abuse disorders, and a number of patients were receiving treatment for those conditions rather than for bipolar disorder. The pervasive comorbidity associated with bipolar disorder suggests disturbances in multiple regulatory systems in this condition, noted Dr. Merikangas.
“Although we could not modify the thresholds for some of the diagnostic criteria for mania and depression, our definition of subthreshold bipolar disorder is still more restrictive than the definitions proposed by clinical researchers,” stated the investigators. “Therefore, our prevalence estimate of subthreshold bipolar disorder is likely to underestimate bipolar spectrum disorder in the population. A related limitation is the absence of information on mixed episodes, rapid cycling, and brief episodes that could be assessed only in more flexible, semistructured clinical interviews.
“In the context of these limitations, the results provide the first nationally representative US general population prevalence estimates of subthreshold bipolar disorder,” the researchers continued. “The inclusion of symptom severity measures also demonstrates the validity of the spectrum concept of bipolarity. The direct association between increasingly restrictive definitions of bipolar disorder and the indicators of clinical validity, including number of episodes, chronicity, symptom severity, impairment, comorbidity, and treatment, provides evidence of the underlying dimensional nature of bipolar illness.”
—Colby Stong
Suggested Reading
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.
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