Many adults with major depression disorder may also be suffering from significant symptoms of bipolar disorder. A new study sponsored by the National Institute of Mental Health (NIMH) has found that almost 40% of adults with a history of major depressive disorder also experience subthreshold hypomania. Hypomania is a form of mania—a symptom of bipolar disorder. Without recognition of hypomania behavior, symptoms of bipolar disorder may go undiagnosed among a large proportion of individuals suffering from major depression. Lead author and investigator Dr. Kathleen Merikangas and her colleagues of NIMH sought to characterize the full spectrum of major mood disorders ranging from major depression to pure mania. The researchers investigated the prevalence of major depressive disorder and the relationships between this disorder and hypomania. Hypomania is considered to be a milder form of mania. A manic episode is a distinct period of elevated, expansive, or irritated mood that lasts for at least one week. When a manic episode occurs, the individual behaves uncharacteristically and may excessively engage in goal-oriented activities or even high-risk activities, such as sexual indiscretions, gambling, or shopping. Episodes may be recurring, cause impairment to the individual’s lifestyle, and sometimes require hospitalization due to psychoses. Hypomania, on the other hand, is distinguished from pure mania symptomatically and categorically. Like mania, a hypomanic episode involves an elevated mood in which the individual displays more activity, energy, self-esteem, racing thoughts, and a lack for sleep due to their agitated state or irritability. Although similar to mania, hypomania lasts fewer than four days and does not impair normal lifestyle, and therefore does not meet the current diagnostic criteria of bipolar disorder. In their study, researchers analyzed data from the National Comorbidity Survey Replication (NCS-R), a national household survey conducted on the adult U.S. population between February 2001 and April 2003. The NCS-R documents Americans’ history of mood disorders, their symptoms, and clinical severity based on the World Health Organization’s Composite International Diagnostic Interview. Based on the responses of 5,692 participants diagnosed with major depressive disorder, researchers found that 40% of participants had a history of subthreshold hypomania. Of this subgroup, depressed individuals had a greater tendency for comorbid disorders such as substance abuse and anxiety, had a younger age at the onset of their depression, displayed more suicide attempts, and had more frequent depressive episodes compared to participants without manic behavior. Most interestingly, depressed participants with hypomania were just as likely to have a family history of mania as individuals with bipolar disorder. This data indicates that the presence of hypomania in depressed individuals increases their risk of having full-blown bipolar disorder later on. Many adults with major depression may actually have subthreshold hypomania—what the researchers are calling a moderate but significant symptom of bipolar disorder. Researchers suggest that their findings support the inclusion of subthreshold hypomania as a diagnostic classification, and may broaden the criteria for bipolar disorder. According to previous research, individuals diagnosed with bipolar disorder more commonly experience hypomania than mania. Similarly, other studies have suggested that individuals with subthreshold hypomania are more likely to develop bipolar disorder than individuals without subthreshold hypomania. This study supports the notion that depression and mania are actually dimensions rather than two distinct clinical diagnoses. Researchers hope that their findings may help health professionals identify their patients’ heightened risk of developing mania when they present recurring episodes of subthreshold hypomania. The researchers’ findings are published this week in the online edition of the American Journal of Psychiatry.