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Bipolar Disorder Health Center

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Bipolar Illness Widely Underdiagnosed

Study Shows More Than 4% of U.S. Adults Affected
WebMD Health News
Reviewed by Louise Chang, MD

May 7, 2007 -- There appear to be almost twice as many Americans with bipolar disorder as previously thought, and many are not getting the treatments they need, researchers from the National Institute of Mental Health report.

Once thought of as a single mental illness, bipolar disorder is increasingly recognized as a spectrum disorder, with symptoms ranging from less severe to devastating.

The NIMH researchers found that people with the mildest form of the condition, often referred to as sub-threshold bipolar disorder, generally sought treatment for other mental health conditions such as depression or substance abuse.

NIMH senior investigator Kathleen R. Merikangas, PhD, says a large percentage of people diagnosed with major depression may actually have this form of bipolar disorder.

"Misdiagnosis is particularly troubling because the drugs used to treat depression can actually trigger bipolar symptoms," she tells WebMD.

What Is Bipolar Disorder?

There are two main types of bipolar disorder (once known as manic depression): bipolar disorder I and bipolar disorder II. Symptoms include dramatic moods swings between euphoria and severe depression; patients may have hallucinations or delusions.

Patients with bipolar I have the most severe symptoms; bipolar II patients have more moderate symptoms.

Study researchers say health professionals should recognize a third and milder category --sub-threshold bipolar disorder.

In 2006, the NIMH estimated that 2.6% of the U.S. population, or roughly 5.7 million American adults, suffered from bipolar disorder in any given year.

By including patients who met the diagnostic criteria for sub-threshold bipolar disorder in their latest analysis, Merikangas and NIMH colleagues concluded that about 4.4% of U.S. adults have some degree of bipolar illness during some point in their lives.

The researchers evaluated data from a nationwide mental disorders survey conducted between February 2001 and April 2003, involving 9,282 adults living in the U.S.

The lifetime incidence of bipolar I and bipolar II was roughly 1% each in the surveyed population and 2.4% for sub-threshold bipolar disorder.

"The [findings] reinforce the argument of other researchers that clinically significant sub-threshold bipolar disorder is at least as common as threshold bipolar disorder," Merikangas and colleagues wrote in the May issue of Archives of General Psychiatry.

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