The Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (DSM-IV-TR) nomenclature for the co-occurrence of manic and depressive symptoms (mixed states) has been revised in the new DSM-5 version to accommodate a mixed categorical-dimensional concept. The new classification will capture subthreshold non-overlapping symptoms of the opposite pole using a "with mixed features" specifier to be applied to manic episodes in bipolar disorder I (BD I), hypomanic, and major depressive episodes experienced in BD I, BD II, bipolar disorder not otherwise specified, and major depressive disorder. The revision will have a substantial impact in several fields: epidemiology, diagnosis, treatment, research, education, and regulations. The new concept is data-driven and overcomes the problems derived from the extremely narrow definition in the DSM-IV-TR. However, it is unclear how clinicians will deal with the possibility of diagnosing major depression with mixed features and how this may impact the bipolar-unipolar dichotomy and diagnostic reliability. Clinical trials may also need to address treatment effects according to the presence or absence of mixed features. The medications that are effective in treating mixed episodes per the DSM-IV-TR definition may also be effective in treating mixed features per the DSM-5, but new studies are needed to demonstrate it.
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