An additional observation, which has been disquieting to patients, families, care-providers, as well as representing a public health priority is suicidality amongst individuals with mood disorders.11,12  Individuals with bipolar disorder may have the highest rates of completed suicide amongst all mental disorders (i.e. with some evidence also indicating similar suicide completion rates amongst individuals with anorexia nervosa). Across subpopulations of bipolar disorder, individuals with mixed features appear to be more likely to experience suicidal ideation, and engage in non-lethal self-harm and completed suicide, when compared to other subpopulations with bipolar disorder.

The foregoing collection of observations, as well as the well-established fact that mixed states, as it was operationalized in DSM-IV-TR, are rarely encountered in clinical practice, provided the impetus for the DSM-5 to eliminate mixed states (i.e. defined as the co-occurrence of syndromal mania and depression) and supplant with the mixed features specifier.

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The DSM-5 introduced in May 2013 by the APA introduced and provided a criteria list for mixed features specifier to be applied to individuals experiencing a major depressive episode (MDE). The mixed features specifier, according to the DSM-5 refers to three or more depressive symptoms in an individual who is experiencing hypo/mania or the occurrence of three or more hypomanic symptoms in an individual experiencing an MDE. In addition to subsyndromal hypomanic symptoms, applying to an individual experiencing an MDE as part of BP-I/II, mixed features specifier during an MDE could also apply in an individual with MDD.13

A legitimate question arises as the extent to which mixed features specifier in an adult with MDD represents a forme fruste of bipolar disorder. Longitudinal studies indicate that approximately 15-25% of individuals with mixed features as part of a depressive episode and no prior hypo/manic episode will eventually declare themselves as having BP-I/II disorder. Consequently, it can be reasonably assumed that MDD with mixed features has phenotypic stability over time.

It is currently estimated that approximately 25-40% of individuals with MDD will exhibit and meet criteria for mixed features specifier as defined in the DSM-5.14 Admittedly with DSM-5, mixed features being a relatively new conception, there are relatively few studies that have employed a rigorous definition of mixed features concordant with DSM-5. Consequently, the preponderance of data has employed varying definitions of mixed features (e.g. depressive mixed states, agitated depression). Notwithstanding, results from the International Mood Disorders Collaborative Project utilizing a DSM-5 definition of mixed features reported that approximately 25% of individuals between 18 and 80 presenting to a University-based mood disorders centre (i.e. University of Toronto, Cleveland Clinic) met full criteria for DSM-5 mixed features specifier as part of MDD.9

Results from the collaborative project study cohere with extant literature insofar as it was additionally reported that adults with MDD and mixed features are more likely to experience psychiatric comorbidity (e.g. anxiety disorders, substance-use disorders), as well as more likely to be reporting impairment across multiple domains of function when compared to those without mixed features. It is a testable hypothesis that the greater degree of functional impairment amongst individuals with mixed features when compared to those without is, in part, due to greater degrees of cognitive impairment in this subpopulation.