Prevalence rates and clinical implications of bipolar disorder "with mixed features" as defined by DSM-5.

Background: We investigated the increase in the prevalence of bipolar disorder with mixed features following the replacement of DSM-IV-TR criteria with DSM-5 criteria. Additionally, we examined the clinical implications of the use of "with mixed features" as a specifier with bipolar disorder.
Method: We retrospectively reviewed medical charts from 2003 to 2013. A total of 331 patients diagnosed with bipolar disorder using the DSM-IV TR were enrolled and categorized into four groups: manic/hypomanic with mixed features, manic/hypomanic without mixed features, depressed with mixed features, and depressed without mixed features. These classifications were made in accordance with the DSM-5 definition of bipolar disorder "with mixed features." Changes in the prevalence, demographic and clinical characteristics were compared among the groups.
Results: The prevalence rates of mixed features were significantly different when using the DSM-5 criteria vs. the DSM-IV-TR criteria. Patients with mixed features had a younger age of onset, younger age at hospitalization, more frequent hospitalizations for mixed episodes, and greater suicide risk compared with patients without mixed features.
Limitations: Retrospective study may have resulted in under diagnosis of mixed states.
Conclusions: An approximately three-fold greater risk for mixed features was observed in patients with bipolar disorder when using the DSM-5 criteria than when using the DSM-IV-TR criteria. The additional patients may represent patients with sub-syndromal mixed features and could indicate that patients with mixed features are underdiagnosed.
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