The Diagnostic Challenge: Is it Depression or Bipolar Disorder?

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Husseini K. Manji, M.D. of Duke University
Husseini K. Manji, M.D.

From The Quarterly, Summer 2011

The depressive symptoms associated with both disorders can make diagnosis a challenge. Major depressive disorder (MDD) is sometimes called unipolar depression – its characteristic mood points in only one direction, “down.” In contrast, bipolar disorder points toward both affective “poles,” both down and up, in cycles whose length and intensity vary from person to person.

The down phase of bipolar disorder (BPD) is major depression, with all of the seriousness experienced in MDD. But in BPD it alternates with a manic “up” mood. “These manic episodes are not pleasant,” explains Dr. Manji. “We’re talking about being excessively revved up; not sleeping; thoughts going a mile a minute. You lose contact with reality—judgment goes out the window. You do reckless things.”

In one variant of bipolar illness called Bipolar II, the mania is called hypomania, and it’s notably milder. For that reason, Bipolar II is often assumed—incorrectly—to be less dangerous. “You are a little more energetic than normal, your thoughts are going a little bit faster; you seem more creative; you’re the life of the party.” But this makes it easy to downplay the situation, or miss a diagnosis. In fact, people with Bipolar II disorder often spend more time depressed than people with Bipolar I.

To be clear: people with Bipolar I and II differ in the intensity of the manic phase, but both suffer from terrible depressions that increase the potential for suicide. Both disorders are also highly recurrent, “another big problem, because there is a temptation to treat what is right in front of you,” says Dr. Manji, regardless of whether it’s the up or down phase. But people with bipolar disorder must be treated for both the depressive and manic phases. And ideally in ways that prevent the emergence of either manic or depressive episodes.

A person with undiagnosed bipolar disorder can be misdiagnosed as “only” having depression if seen by a doctor during a “down” phase. The problem is that some patients are indeed only depressed – they have MDD, but not bipolar disorder. How can someone going through his or her first major depressive episode know? This is a challenge for the diagnosing physician, because there is a natural temptation to prescribe an antidepressant drug to control the depression. But, Dr. Manji notes, antidepressants can actually trigger hypomania/mania in people who have bipolar disorder and are not “just” depressed. So the question becomes: who is depressed, and who is depressed but also manic?

In fact, a doctor has no way of knowing for certain when treating a young patient for a first depressive episode and no prior history of mania. The doctor will take a very careful history, hoping to identify any previous episodes of mania or depression, which may have been missed. However, no biological test yet exists for diagnosing any mood disorder; thus, “when the index of suspicion for bipolarity is high,” Dr. Manji says, “the usual course of action is to give the first-time patient a mood-stabilizing drug, such as lithium, rather than, say, only an antidepressant like Prozac.”

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