Merikangas, from the National Institute of Mental Health in Bethesda, Maryland, and her team evaluated the rates and treatment patterns of bipolar spectrum disorder in a representative sample of the U.S. population that included 9,282 subjects. Bipolar disorder was diagnosed based on responses to the Composite International Diagnostic Interview.
The lifetime prevalence for bipolar disorder 1 was 1.0 percent, for bipolar disorder 2 it was 1.1 percent, and for subthreshold bipolar disorder it was 2.4 percent, the investigators report. During the previous 12 months, the corresponding prevalence was 0.6 percent, 0.8 percent, and 1.4 percent, respectively.
The investigators defined subthreshold bipolar disorder as recurrent hypomania (mild hypomania) without a major depressive episode or with fewer symptoms than required for threshold hypomania.
"One criticism we always get is that we're 'medicalizing' everything" and artificially inflating prevalence rates, Merikangas said, instead of recognizing symptoms as "the normal ups and downs of life." However, bipolar disorder, including subthreshold bipolar disorder, "really does impair people," she stated.
Study results verify the clinical severity of the disorder, the team maintains, as reflected by the number of episodes, chronicity, symptom severity, impairment and the presence of other illnesses. The observation of increasing symptom severity from one category to the next reinforces "the validity of the spectrum concept of bipolarity," the researchers note.
Merikangas explained that distinguishing the three classifications of bipolar disorder is a matter of degree. "The core feature is recurrence and fluctuation between mood states."
Manic episodes are characterized by euphoria and elevated self-esteem, lasting more than 1 week. Symptoms of hypomania include "increased motor activity, feeling agitated instead of happy, thoughts going too fast, they're distractible, and they can't concentrate."
After a hypomanic episode, "individuals may experience an episode of lethargy, where they can't even get out of bed," she said.
The investigators also found that many of the subjects were being treated for depression, and few - no more than 25 percent -- were taking mood stabilizers.
"Mood stabilizers are necessary for amelioration of symptoms of bipolar disorder," Merikangas said. "Antidepressants don't seem to benefit bipolar disorder patients during a depressive episode. Instead, bipolar patients are apt to become more agitated."
"It's important to make the right diagnosis, because of treatment differences and consequences," she concluded. "Bipolar disorder is much more likely to be associated with subsequent substance use disorders, suicide, and some medical disorders."
SOURCE: Archives of General Psychiatry, May 2007.
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