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Symptoms of Bipolar Disorder May Go Undiagnosed in Some Adults with Major Depression

Science Update

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Nearly 40 percent of people with major depression may also have subthreshold hypomania, a form of mania that does not fully meet current diagnostic criteria for bipolar disorder, according to a new NIMH-funded study. The study was published online ahead of print August 15, 2010, in the American Journal of Psychiatry.

Background

Mania is a symptom of bipolar disorder. According to the Diagnostic and Statistical Manual for Mental Disorders (DSM-IV), it is generally defined as a discrete period of increased energy, activity, euphoria or irritability that leads to marked impairment in one’s daily life. The DSM-IV states that a manic episode lasts for one week or more, and may sometimes require hospitalization.  Hypomania is defined as a milder form of mania that lasts for four days at a time, but does not interfere with one’s daily activities. The majority of people diagnosed with bipolar disorder experience repeated episodes of hypomania rather than mania.

For this new study, Kathleen Merikangas, PhD., of NIMH, and colleagues aimed to characterize the full spectrum of mania by identifying hypomanic episodes that last less than four days among those diagnosed with major depression. They described this type of hypomania as subthreshold hypomania. Merikangas and colleagues used data from 5,692 respondents of the National Comorbidity Survey Replication (NCS-R), a nationally representative survey of American adults ages 18 and older.

Results of the Study

The researchers found that nearly 40 percent of those identified as having major depression also had symptoms of subthreshold hypomania. Compared to those with major depression alone, those with depression plus subthreshold hypomania tended to be younger at age of onset and to have had more coexisting health problems, more episodes of depression and more suicide attempts.  They also found that among those with subthreshold hypomania, a family history of mania was just as common as it was among people with bipolar disorder.

Significance

According to the researchers, the findings indicate that many adults with major depression may in fact have mild but clinically significant symptoms of bipolar disorder.  In addition, because many with subthreshold hypomania had a family history of mania, the researchers suggest that subthreshold hypomania may be predictive of future hypomania or mania. Previous research has indicated that young people with subthreshold hypomania symptoms are more likely to develop bipolar disorder over time, compared to those without subthreshold hypomania, said the authors. 

What’s Next

The researchers suggest that depression and mania may be defined as dimensions, rather than as discrete diagnostic categories. Clinicians should be aware that patients who report repeated episodes of subthreshold hypomania may have a risk of developing mania, the researcher concluded.

Reference

Angst J, Cui L, Swendsen J, Rothen S, Cravchik A, Kessler R, Merikangas K. Major depressive disorder with sub-threshold bipolarity in the National Comorbidity Survey Replication. American Journal of Psychiatry. Online ahead of print August 15, 2010.