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Is underdiagnosis the main pitfall in diagnosing bipolar disorder? No

BMJ 2010; 340 doi: https://doi.org/10.1136/bmj.c855 (Published 22 February 2010) Cite this as: BMJ 2010;340:c855
  1. Mark Zimmerman, director, outpatient psychiatry
  1. 1Rhode Island Hospital, Bayside Medical Building, 235 Plain Street, Providence, RI 02905, USA
  1. mzimmerman{at}lifespan.org

    Daniel Smith and Nassir Ghaemi (doi:10.1136/bmj.c854) believe that many people with bipolar disorder remain undiagnosed, but Mark Zimmerman argues that overdiagnosis is the bigger problem

    Bipolar disorder is a serious illness resulting in significant psychosocial morbidity and excess mortality. Research reports, reviews, and commentaries have suggested that bipolar disorder is under-recognised, and that many depressed patients have, in fact, bipolar disorder.1 2 3 4 The treatment and clinical implications of the failure to recognise bipolar disorder in depressed patients include the underprescription of mood stabilising drugs, an increased risk of rapid cycling, and increased costs of care.5 6 7 8

    During the past decade, my hospital has introduced semistructured diagnostic interviews into outpatient clinical practice. Use of these interviews initially documented underdetection of psychiatric comorbidity,9 10 11 and these findings were replicated in other settings.12 13 14 However, in recent years, we observed the emergence of an opposite phenomenon in bipolar disorder —clinician overdiagnosis in patients without a history of a manic or hypomanic episode.

    Overdiagnosis is the bigger problem

    We therefore conducted a study to determine how often bipolar disorder might be overdiagosed and underdiagnosed.15 We interviewed 700 psychiatric outpatients with the structured clinical interview for DSM-IV (SCID), a widely used, validated, diagnostic interview. About a fifth of the sample reported having had bipolar disorder diagnosed (145, 21%), significantly higher than the number we diagnosed with the structured interview (90, (13%), P<0.001). Only 63 (43%) of the 145 patients who reported a previous diagnosis of bipolar disorder had the condition diagnosed by the structured interview. Bipolar disorder was also underdiagnosed in some patients, but three times as many patients had been overdiagnosed as had been underdiagnosed (82 v 27).

    Supporting the validity of our diagnoses of bipolar disorder, we found that the patients who were previously wrongly diagnosed with bipolar disorder were significantly less likely to have a first degree relative with bipolar disorder than patients who were accurately diagnosed with bipolar disorder. The proportion with affected relatives in the overdiagnosed patients was the same as in patients who never had bipolar disorder diagnosed.

    Although other studies have reported overdiagnosis of bipolar disorder, we are aware of only one other study with data on both overdiagnosis and underdiagnosis. Hirschfeld and colleagues16 interviewed 180 depressed primary care outpatients receiving antidepressant drugs with the structured clinical interview for DSM-IV. Forty three patients reported a prior diagnosis of bipolar disorder, and this diagnosis was not confirmed in 14 (33%). The overdiagnosis rate of 33% was higher than the 22% underdiagnosis rate in the 137 patients who had not had bipolar disorder previously diagnosed.

    Thus, the only two studies examining both underdiagnosis and overdiagnosis have both found evidence that overdiagnosis is a greater problem than underdiagnosis.

    Accuracy is crucial

    Whether bipolar disorder is more frequently overdiagnosed or underdiagnosed is not really important. Rather, it is critical that it is accurately diagnosed. Use of thorough diagnostic evaluations is important to detect bipolar disorder. Consistent with other studies, we found that nearly one third of the patients we diagnosed with bipolar disorder were previously undiagnosed.

    However, most discussions of the misdiagnosis of bipolar disorder have focused on the personal and societal costs of underdiagnosis. Only occasionally have authors discussed the possible problems associated with overdiagnosis. Unnecessary side effects are a potentially serious consequence of overdiagnosis. Mood stabilisers are the treatment of choice for bipolar disorder and, depending on the drug, can affect renal, endocrine, hepatic, immunological, or metabolic function. Thus, overdiagnosing bipolar disorder can unnecessarily expose patients to serious drug side effects.

    Causes of overdiagnosis

    Why might the phenomenon of false positive bipolar disorder diagnoses be arising at this time? One important answer is likely to be the increased availability of drugs to treat bipolar disorder and the accompanying marketing efforts. Many continuing medical education programmes on bipolar disorder begin with a summary of research suggesting bipolar disorder is underdiagnosed, and this is followed by a discussion of methods clinicians can use to improve the detection of the disorder. These discussions of diagnostic practice are usually not balanced by a summary of studies of showing overdiagnosis and the risks associated with overdiagnosis. Because clinicians are probably inclined to diagnose disorders that they feel more comfortable treating, when confronted with patients with mood instability who do not meet criteria for a hypomanic episode, doctors may nonetheless diagnose a potentially drug responsive disorder such as bipolar disorder rather than a disorder such as borderline personality disorder that is less responsive to drugs.

    Use of screening scales, such as the mood disorders questionnaire, for bipolar disorder can also result in overdiagnosis. Screening questionnaires prioritise sensitivity, at a cost of false positive results, because it is presumed that they are followed by expert clinical evaluation. Insufficient diagnostic rigour after the use of screening scales can result in greater rates of overdiagnosis. Routine use of bipolar disorder screening scales is not supported by the data and does not make conceptual sense.17

    Notes

    Cite this as: BMJ 2010;340:c855

    Footnotes

    • Competing interests: The author has completed the unified competing interest form at www.icmje.org/coi_disclosure.pdf (available on request from the corresponding author) and declares (1) no financial support for the submitted work from anyone other than their  employer; (2) no financial relationships with commercial entities that might have an interest in the submitted work; (3) no spouses, partners, or children with relationships with commercial entities that might have an interest in the submitted work; and (4) no non-financial interests that may be relevant to the submitted work.

    References

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