Sun, Nov 30, 2008 page9

• Overdiagnosis of bipolar disorder may be worse than the illness

  • By Mark Zimmerman
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  During the past few years, many experts have suggested that bipolar disorder — a serious illness resulting in significant psychosocial morbidity and excess mortality — is under-recognized, particularly in patients with major depression. Even patients who are diagnosed with bipolar disorder often wait more than 10 years after initially seeking treatment for the correct diagnosis to be made.

  The clinical implications of the failure to recognize bipolar disorder in depressed patients include the under-prescription of mood-stabilizing medications, and an increased risk of rapid “cycling” — swings between manic and depressive phases. But, perhaps as a consequence of concerted efforts to improve the recognition of bipolar disorder, during the past few years we have observed the emergence of an opposite phenomenon — overdiagnosis.

  In my own practice, my colleagues and I have encountered patients who reported that they were previously diagnosed with bipolar disorder, despite lacking a history of manic or hypomanic episodes. To be sure, we have also seen patients seeking treatment for depression who really did have bipolar disorder. However, there seemed to be more overdiagnosis than underdiagnosis.

  We therefore conducted a study to examine empirically how often bipolar disorder might be over- and under-diagnosed. Seven hundred psychiatric outpatients were interviewed with the Structured Clinical Interview for DSM-IV (SCID) and completed a self-administered questionnaire that asked whether they had been previously diagnosed by a health-care professional with bipolar or manic-depressive disorder. Family history information was obtained from the patient regarding their immediate relatives.

  Slightly more than 20 percent (145 patients) in our sample reported that they had been previously diagnosed as having bipolar disorder, significantly higher than the 12.9 percent rate based on the SCID. Less than half of those who reported that they had been previously diagnosed with bipolar disorder were diagnosed with bipolar disorder based on the SCID. Patients with SCID-diagnosed bipolar disorder had a significantly higher risk of bipolar disorder in their immediate family members than patients who self-reported a previous diagnosis of bipolar disorder that was not confirmed by the SCID. Patients who self-reported a previous diagnosis of bipolar disorder that was not confirmed by the SCID did not have a significantly higher risk for bipolar disorder than the patients who were negative for bipolar disorder by self-report and the SCID. Our findings, validated by family history, thus suggest that bipolar disorder was overdiagnosed.

  Any study seeking to determine whether a psychiatric disorder is over-diagnosed will find that some patients with the condition do not have it upon re-interview. Such is the nature of the imperfect reliability of psychiatric diagnosis. The question, then, is not whether some patients previously given a diagnosis do not seem to have it upon re-interview, but rather how many . How high the percentage should be before claiming over-diagnosis is a significant problem and a value judgment. But we think that an over-diagnosis rate of more than 50 percent crosses the clinical significance threshold.

  Over-diagnosis of bipolar disorder has costs. Mood stabilizers are the treatment of choice, and, depending on the medication, they can produce potentially significant health complications affecting renal, endocrine, hepatic, immunologic, or metabolic function.

  The impact of marketing efforts by pharmaceutical companies and publicity probably plays a role in the emerging tendency to over-diagnose bipolar disorder. Direct-to-consumer advertisements that refer individuals to screening questionnaires can result in patients suggesting to their doctors that they have bipolar disorder. We have seen evidence of this in our practice. This does not necessarily reflect a problem with the performance of a screening questionnaire, but rather how these scales are used. Screening questionnaires maximize sensitivity, at a cost of false positives, because it is presumed that they are followed by expert clinical evaluation. But insufficient diagnostic rigor can result in overdiagnosis.

  Clinicians are inclined to diagnose disorders that they feel more comfortable treating. We believe that the increased availability of medications that have been approved for the treatment of bipolar disorder might be influencing clinicians who are unsure whether or not a patient has bipolar disorder or borderline personality disorder to err on the side of diagnosing the disorder that is responsive to medication.

  This bias is reinforced by the marketing of pharmaceutical companies to physicians, which has emphasized research on delayed diagnosis and under-recognition of bipolar disorder, possibly sensitizing clinicians accordingly. The campaign against under-recognition has probably resulted in some anxious, agitated and/or irritable depressed patients who complain of insomnia and “racing thoughts” being misdiagnosed with bipolar disorder.

  The results of our study are consistent with prior studies suggesting possible problems with the diagnosis of bipolar disorder. With the greater number of medications approved for the treatment of bipolar disorder, along with multiple reports cautioning clinicians against underdiagnosis, it appears that overdiagnosis has become a greater problem than underdiagnosis. Both can have negative consequences.

  Mark Zimmerman is associate professor of psychiatry and human behavior at Brown Medical School.

  COPYRIGHT: PROJECT SYNDICATE
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