Bipolar disorder is a brain disease, or group of diseases, associated with periods of depressed mood as well as periods of particularly elevated or irritable mood. Although generally episodic, it is nearly always recurrent and lifelong. Recent epidemiologic data confirm that bipolar disorder is both chronic and disabling.1 Bipolar disorder is associated with significant mortality; lifetime risk of death from suicide approaches 20 times that of the general population.2 Likewise, bipolar disorder contributes substantially to disability as well as medical costs,3 ranking as the sixth-leading contributor to disability in 1990 World Health Organization figures.
A number of studies also suggest that patients with bipolar disorder are frequently misdiagnosed with other disorders. Two surveys among patients with bipolar disorder, conducted a decade apart, suggested little change in the rate of misdiagnosis.4,5 The most recent survey4 noted that 69% of patients with bipolar disorder reported an initial misdiagnosis, with more than one third experiencing a delay of 10 years or greater before receiving a diagnosis of bipolar disorder. Likewise, a European survey of more than 1000 individuals with bipolar disorder found a mean time to correct diagnosis of 5.7 years.6
Of note, such a survey-based approach may overestimate rates of misdiagnosis for several reasons. First, it assumes that the current diagnosis is correct—that is, that the patient actually does have bipolar disorder. A problem in studying bipolar disorder, as with psychiatric illness in general, is the absence of a true gold standard. Second, response rates in these surveys were relatively low, increasing susceptibility to response bias. For example, patients with longer delays in diagnosis might be more likely to join an advocacy group or respond to a survey about treatment. Nonetheless, regardless of the actual rates, these surveys clearly establish that a substantial number of patients with bipolar disorder are misdiagnosed.
Consequences of Misdiagnosis
The consequences of misdiagnosis can be profound. In the absence of effective treatment, patients may experience a greater number of recurrences or more long-term episodes. Not surprisingly, both of these can have profound effects on patient functioning as well as medical costs. Recurrent mood episodes can substantially impair patients' ability to maintain relationships as well as education and employment. Moreover, even after recovery, the episodes may have enduring and cumulative consequences—for example, a patient who loses jobs because depression makes it impossible to get to work on time, or because manic episodes lead to conflict with coworkers or even legal involvement, may find it increasingly difficult to find employment. Family members, friends, or partners may grow tired of unpredictable moods or early morning crises.
In some cases, misdiagnosis may contribute to iatrogenic injury. Debate continues over the magnitude of risk associated with antidepressant treatment in bipolar disorder.7,8 A subset of patients with bipolar disorder exposed to antidepressants may experience "switch"—that is, induction of a manic or mixed state (simultaneous symptoms of mania and depression). With older antidepressants, such as tricyclics—desipramine or nortriptyline, for example—the risk may be particularly great. Some risk of mania induction exists with newer antidepressants, but the magnitude is difficult to estimate and probably somewhat less.8
A second and less widely-appreciated risk with antidepressants is cycle acceleration.9,10 In this condition, patients experience more frequent episodes than before antidepressant initiation. Without careful monitoring, cycle induction is not always readily apparent—patients may describe a positive antidepressant response initially but loss of response some months later, which may lead to dose increase or use of additional antidepressants. A typical patient might describe episodes every 2 to 3 years before beginning antidepressant treatment, with episodes every year thereafter, despite an "excellent" initial response to treatment.
Finally, although the link between effective treatment and reduction in suicide risk is difficult to establish definitively, by depriving patients of an effective treatment, an opportunity to decrease suicide risk may be missed.11
Contributors to Misdiagnosis
The particular factors that contribute to misdiagnosis in bipolar disorder have not been studied rigorously, but some of them appear to be relatively straightforward. To begin with, patients may provide poor or uneven history, particularly during acute mood episodes. Some patients with depression will state that they have "always" been depressed or cannot recall ever feeling better. Likewise, mildly elevated patients may fail to report important symptoms (such as racing thoughts or a decreased need for sleep) if they fail to perceive them as pathological. In some cases, fear of stigma may lead patients to deliberately underreport symptoms of mania or hypomania: for many, a diagnosis of depression is much more palatable than bipolar disorder. This concern occasionally extends to clinicians as well, who may be reluctant to make this diagnosis in the absence of absolute certainty.
An additional source of diagnostic complexity is psychiatric comorbidity, which is the norm rather than the exception among patients with bipolar disorder.1,12 More than 50% experience at least 1 comorbid anxiety disorder, including generalized anxiety or panic disorder. Some of the features of anxiety and depression or hypomania/mania may overlap—for example, impaired concentration can be associated with all 3, as can sleep disruption. Anxious patients, as well as manic patients, may report racing thoughts. Thus, a clinician who stops with a patient's chief complaint of anxiety may miss more subtle symptoms of bipolar disorder.
Other common comorbidities in patients with bipolar disorder are substance abuse and dependence, which are often present at initial presentation.13 Alcohol and stimulants can produce symptoms that mimic mood episodes; for patients with ongoing substance use, it can therefore be difficult to discern the presence of an underlying mood disorder.