NIMH researcher Kathleen Merikangas, Ph.D. and colleagues identified prevalence rates of three subtypes of bipolar spectrum disorder among adults. Bipolar I is considered the classic form of the illness, in which a person experiences recurrent episodes of mania and depression. People with bipolar II experience a milder form of mania called hypomania that alternates with depressive episodes.

People with bipolar disorder not otherwise specified (BD-NOS), sometimes called subthreshold bipolar disorder, have manic and depressive symptoms as well, but they do not meet strict criteria for any specific type of bipolar disorder noted in the Diagnostic and Statistical Manual for Mental Disorders (DSM-IV), the reference manual for psychiatric disorders. Nonetheless, BD-NOS still can significantly impair those who have it.

The results indicate that bipolar I and bipolar II each occur in about 1 percent of the population; BD-NOS occurs in about 2.4 percent of the population. The findings support international studies suggesting that, given its multi-dimensional nature, bipolar disorder may be better characterized as a spectrum disorder.

"Bipolar disorder can manifest itself in several different ways. But regardless of type, the illness takes a huge toll," said NIMH Director Thomas R. Insel, M.D. "The survey's findings reiterate the need for a more refined understanding of bipolar symptoms, so we can better target treatment."

Most respondents with bipolar disorder reported receiving treatment. Nearly everyone who had bipolar I or II (89 to 95 percent) received some type of treatment, while 69 percent of those with BD-NOS were getting treatment. Those with bipolar I or II were more commonly treated by psychiatric specialists, while those with BD-NOS were more commonly treated by general medical professionals.

However, not everyone received treatment considered optimal for bipolar disorder. Up to 97 percent of those who had some type of bipolar illness said they had coexisting psychiatric conditions, such as anxiety, depression or substance abuse disorders, and many were in treatment for those conditions rather than bipolar disorder.

The researchers found that many were receiving medication treatment considered "inappropriate" for bipolar disorder, e.g., they were taking an antidepressant or other psychotropic medication in the absence of a mood stabilizing medication such as lithium, valproate, or carbamazepine. Only about 40 percent were receiving appropriate medication, considered a mood stabilizer, anticonvulsant or antipsychotic medication.

"Such a high rate of inappropriate medication use among people with bipolar spectrum disorder is a concern," said Dr. Merikangas. "It is potentially dangerous because use of an antidepressant without the benefit of a mood stabilizer may actually worsen the condition."

Merikangas and colleagues speculate that as people seek treatment for anxiety, depression or substance abuse disorders, their doctors, especially if they are not mental health specialists, may not be detecting an underlying bipolar condition in their patients."Because bipolar spectrum disorder commonly coexists with other illnesses, it is likely underrecognized, and therefore, undertreated. We need better screening tools and procedures for identifying bipolar spectrum disorder, and work with clinicians to help them better spot these bipolar symptoms," concluded Dr. Merikangas.

 The NCS-R was funded by the National Institutes of Health's National Institute of Mental Health (NIMH).

Reference: Merikangas KR, et al. Lifetime and 12-Month Prevalence of Bipolar Spectrum Disorder in the National Comorbidity Survey Replication. Archives of General Psychiatry. May 2007; 64.

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