WebMD Medical News
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
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
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.
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.
Most people who met the clinical definition of sub-threshold bipolar
disorder (70%) were already receiving treatment when surveyed. Many were taking
antidepressants, according to
Depression, substance abuse, and anxiety disorder are all conditions
commonly seen in bipolar disorder patients, complicating the diagnosis of
less severe bipolar illness.
As a result, mood-stabilizing drugs such as lithium, which are most
effective for treating bipolar illness, are widely underprescribed while
antidepressants are being prescribed far too often, Merikangas says.
The researchers conclude that clinicians who treat patients for depression,
anxiety, or substance abuse must develop a higher suspicion of bipolar
"Bipolar disorder can manifest itself in several different ways. But
regardless of type, the illness takes a huge toll," NIMH Director Thomas R.
Insel, MD, says in a news release.
"The survey's findings reiterate the need for a more refined
understanding of bipolar symptoms so we can better target treatment."
SOURCES: Merikangas, K.R. Archives of General Psychiatry, May 2007;
vol 64: pp. 543-552. Kathleen R. Merikangas, PhD, senior investigator,
intramural research program, National Institute of Mental Health, Bethesda, Md.
Thomas R. Insel, MD, director, National Institute of Mental Health. "The
Numbers Count: Mental Disorders in America," National Institute of Mental
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