Is bipolar disorder overdiagnosed?

A new study by Rhode Island Hospital and Brown University researchers reports that fewer than half the patients previously diagnosed with bipolar disorder received a diagnosis of bipolar disorder based on a comprehensive, psychiatric diagnostic interview--the Structured Clinical Interview for DSM-IV (SCID).

The study concludes that while recent reports indicate that there is a problem with underdiagnosis of bipolar disorder, an equal if not greater problem exists with overdiagnosis. The study was published online by the Journal of Clinical Psychiatry. Principle investigator Mark Zimmerman, M.D., will present the findings at the annual meeting of the American Psychiatric Association on Wednesday, May 7.

The study method involved 700 psychiatric outpatients who were interviewed using the SCID and completed a self-administered questionnaire between May 2001 and March 2005. The questionnaire asked patients whether they had been previously diagnosed with bipolar or manic-depressive disorder by a health care professional. Family history of bipolar disorder was used as an index of diagnostic validity.

Of the 700 patients, 145 reported they had been previously diagnosed as having bipolar disorder; however, fewer than half of the 145 patients (43.4 percent) were diagnosed with bipolar disorder based on the SCID. Further, the study showed that patients diagnosed with bipolar disorder based on the SCID had a significantly higher morbid risk of bipolar disorder in first-degree relatives.

Unnecessary side effects are a significant concern of overdiagnosis. Because mood stabilizers are the treatment of choice for bipolar disorder, overdiagnosing can unnecessarily expose patients to serious medication side effects, including possible impact to renal, endocrine, hepatic, immunologic and metabolic functions.

Lead author Mark Zimmerman, M.D., director of outpatient psychiatry at Rhode Island Hospital and associate professor of psychiatry and human behavior at The Warren Alpert Medical School of Brown University, notes, “Clinicians are inclined to diagnose disorders that they feel more comfortable treating. We hypothesize 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 medication responsive.” He continues, “This bias is reinforced by the marketing message of pharmaceutical companies to physicians, which has emphasized the literature on the delayed and underrecognition of bipolar disorder, and may be sensitizing clinicians to avoid missing the diagnosis of bipolar disorder.”

Zimmerman concludes, “The results of this study suggest that bipolar disorder is being overdiagnosed and we recommend that clinicians use a standardized, validated method in diagnosing bipolar disorder.”

The report is from the Rhode Island Methods to Improve Diagnostic Assessment and Services (MIDAS) Project, for which Zimmerman is the principal investigator. Zimmerman said, “The MIDAS project is unique in its integration of research quality diagnostic methods into a community-based outpatient practice affiliated with an academic medical center.”

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May 6, 2008