Many people diagnosed with depression actually may have a mild form of bipolar disorder.
According to Dr. Kathleen R. Merikangas from the National Institute of Mental Health and her colleagues, “Nearly 40 percent of people with a history of major depressive disorder report periods of hypomania that just miss the threshold for a bipolar diagnosis.”
Bipolar disorder, formerly known as manic depression, is a mental disorder characterized by alternating “highs” (what clinicians call mania) and “lows” (depression). Bipolar disorder affects about 2.6 percent of the U.S. population, according to the National Institute of Mental Health. People with bipolar disorder are generally diagnosed with one of several types: bipolar I, bipolar II, or cyclothymia. Bipolar I disorder patients have more severe mood swings, with periods of mania alternating with depression. Bipolar II patients experience alternating periods of depression and hypomania (a milder version of mania). People with cyclothymia have mood swings as well, but not severe enough to be diagnosed with bipolar disorder. Clinicians and researchers are becoming aware that there is a spectrum from major depression to pure mania.
To assess how often people with depression have subtle, undiagnosed bipolar symptoms, Merikangas and her team examined 9,282 people people surveyed in the National Comorbidity Survey Replication (NCS-R).
“The NCS-R is a nationally representative face-to-face household survey of the U.S. population conducted between February 2001 and April 2003. Lifetime history of mood disorders, symptoms, and clinical indicators of severity were collected using version 3.0 of the World Health Organization’s Composite International Diagnostic Interview,” writes Merikangas.
The team found that of the 9,282 people in the survey, 5.4 percent met criteria for major depressive disorder alone over the prior 12 months and 10.2 percent had a history of depression.
2.2 percent had major depression with subthreshold hypomania over the prior 12 months, and 6.7 percent had a lifetime history of depression with subthreshold hypomania.
Bipolar I disorder affected 0.3 percent of the respondents over the prior 12 months and 0.7 percent over their lifetime; bipolar II affected 0.8 percent, and cyclothymia 1.6 percent, respectively.
Added together, the bipolar spectrum conditions were nearly as common as major depression alone.
Almost 40 percent of people with a history of depression described periods with hypomanic symptoms that were just below the threshold for a diagnosis of bipolar disorder. These individuals tended to be younger when symptoms began, have more episodes of depression, have more anxiety, substance abuse, behavioral problems, and higher rates of suicide than those without subtle hypomanic symptoms. However, the severity of their illness was lower than those diagnosed with bipolar II.
In addition, those with a history of subthreshold hypomania had a family history of mania at the same rate as those diagnosed with mania themselves.
Those with subthreshold hypomanic symptoms and those with depression alone received treatment at the same rates.
Although subthreshold mania is not a diagnosis in the current edition of the Diagnostic and Statistical Manual of Mental Diseases (DSM-5), a revision is due in 2013. Merikangas suggests that adding subthreshold bipolarity could be beneficial. “These findings demonstrate heterogeneity in major depressive disorder and support the validity of inclusion of subthreshold mania in the diagnostic classification. The broadening of criteria for bipolar disorder would have important implications for research and clinical practice,” write the authors.
“Such an expansion of the bipolar concept would likely lead to important changes in the treatment of patients who are undiagnosed or misdiagnosed despite elevated morbidity and mortality rates.”
These results are important not only for researchers, but for clinicians. In evaluating patients with major depression, clinicians can be aware of the possibility of subthreshold hypomania, and the tendency for these patients to have a poorer outcome than those with depression alone. Merikangas’s group suggests that enquiring about family history of mania can be especially helpful in evaluating this group. Furthermore, some of these patients may benefit from the addition of a mood stabilizer in addition to antidepressant therapy.
Dr. Merikangas’s results can be found in the August online edition of the American Journal of Psychiatry.
Source: American Journal of Psychiatry