Differentiating Major Depressive Disorder and Bipolar Depression

CASE PRESENTATION Amrita is a 28-year-old woman previously diagnosed with major depressive disorder (MDD). She has had several depressive episodes from ages 18 to 21 years. Amrita is currently employed as a loan officer at a community bank and has a 3-year-old daughter. She has been referred to your psychiatric practice by her primary care provider, who is concerned that her depression is nonresponsive to treatment. Amrita complains of feeling sad and "empty" on most days and reports anhedonia and insomnia. She describes "moving slowly" and has had difficulties working and caring for her daughter. She has a history of migraines and hypothyroidism managed with levothyroxine. She has had a partial response to sertraline but still reports being "down most days." An important question for this patient with symptoms of depression is whether she has had episodes of feeling energetic and times when she was not her usual self. When asked, Amrita reports a 2-week period when her depression "improved"; this interval was characterized by high productivity and lack of need for sleep (sleeping only 3 or 4 hours per night). Diagnosing Bipolar Depression Diagnosing bipolar depression can be challenging, and it is probably the most misdiagnosed phase of the bipolar disorder spectrum. Many patients with bipolar depression are initially diagnosed and treated for MDD. (1) The consequences of misdiagnosis and improper treatment of bipolar depression can be considerable. Patients misdiagnosed with MDD are usually treated with antidepressant monotherapy, which is not efficacious and may be associated with a risk of mood switching. (1,2) The extent of misdiagnosis was highlighted by the results of a survey of 600 patients with bipolar disorder in the National Depressive and Manic-Depressive Association advocacy group. (3) Although more than one-third sought professional care within 1 year of symptom onset, 69% were misdiagnosed, principally with unipolar depression. Among those misdiagnosed, patients consulted an average of 4 psychiatrists before being correctly diagnosed. For one-third of patients, it took at least 10 years to receive an accurate diagnosis. Another study showed that among outpatients (n=649) receiving treatment for depression, 21% screened positive for bipolar disorder, most of whom had never been diagnosed. (4) In a study of 501 patients with bipolar disorder, the mean interval between the first episode and treatment was 9.6 years. (5) Longer duration of untreated bipolar depression was associated with more mood episodes and suicidal behavior, (5) and an increasing number of previous episodes was associated with poorer outcomes once treatment was started. (6,7) Bipolar depression has a considerable impact on patients. Two long-term prospective studies that assessed the natural history of weekly symptom status in patients with bipolar disorder demonstrated the burden of depression in these patients. (8,9) In a study of 146 patients with bipolar I disorder, depressive symptoms were 3 times as frequent as manic/hypomanic symptoms (31.9% vs 8.9% of follow-up weeks) and 5 times more frequent than cycling/mixed symptoms (5.9% of follow-up weeks). (8) In a companion study of 86 patients with bipolar II disorder, depressive symptoms were even more predominant (50.3% of follow-up weeks), compared with hypomanic symptoms (1.3%) and cycling/mixed symptoms (2.3%). (9) Although bipolar I disorder is characterized by episodic mania, the severity of bipolar depression is greater in patients with bipolar II disorder (50.3% vs 31.9% of follow-up weeks). (8,9) Depressive symptoms are also more troublesome to social adjustment than are manic symptoms. In a survey of 593 patients with bipolar disorder, self-reported depressive symptoms were more frequent than manic symptoms and were associated with significantly greater disruption of occupational, social, and family functioning. (10) Further, an increasing body of evidence suggests that the predominant mood polarity is an important prognostic indicator in patients with bipolar disorder and may have implications for long-term treatment. …