Objective: Bipolar disorder is frequently misdiagnosed as major depressive disorder (MDD). We aim to quantify the prevalence of misdiagnosed bipolar disorder among the depression population and evaluate the quality-of-life (QOL) impact of misdiagnoses.
Method: Data were collected from 2 self-administered, cross-sectional studies in 2003. Patients participating in The Bipolar Disorder Misdiagnosis Study (N = 1156) were previously diagnosed with depression, experienced a depressive episode within the past year, and had no previous diagnosis of bipolar disorder or schizophrenia. Patients who experienced a manic episode in the past year, based on DSM-IV criteria, were classified as misdiagnosed. Patients participating in The Bipolar Disorder Project (N = 1214) self-reported a diagnosis of bipolar disorder and were recruited through community mental health centers and support groups. Quality of life was assessed via the Psychological General Well-Being (PGWB) Index and Medical Outcomes Study 8-Item Short-Form Health Survey (SF-8). Demographic differences between groups were controlled using linear regression models.
Results: Of the diagnosed MDD sample, 14.3% met criteria for misdiagnosed bipolar disorder. When controlling for demographic differences, the PGWB overall score for the misdiag-nosed averaged 12.77 (p < .001) points lower than that of MDD patients and 9.55 (p < .001) points lower than that of diagnosed bipolar disorder patients. The average SF-8 mental component summary score for the misdiagnosed was 5.85 (p < .001) points lower than that of MDD patients and 3.18 (p = .002) points lower than that of diagnosed bipolar disorder patients.
Conclusion: Misdiagnosis is associated with poorer QOL than MDD or diagnosed bipolar disorder, which are recognized as having a considerable impact on QOL.