Mixed features have been described in the psychiatric literature for over a century. The original author of the word (and/or concept) has been debated, with many experts believing that German physician Johann Christian August Heinroth may be the original author. Mixed states were described and ostensibly codified by German psychiatrist Emil Kraepelin as part of the “Manic Depression Spectrum.”
According to Kraepelin’s tripartite dimensional model, individuals with “non-dementing disorders” could be conceptualized (and consequently categorized) as experiencing a disturbance along three dimensions (i.e. mood, thought, and volition).1 Kraepelin posited that individuals exhibiting elevation in all three tri-partite dimensions would be most accurately labelled as “manic,” while individuals with reduction would be referred to as “melancholic.” He proposed that six mixed states existed, largely comprised of combinations of elevation or reduction in one or more of the three dimensions.
The conceptual framework proposed by Kraepelin provided not only a heuristic, but also a codification process, wherein individuals without dementia praecox could be diagnosed and differentiated with the utmost of precision available at the time. The dimensional approach to conceptualizing and diagnosing affective disorders was the prevailing approach in psychiatry until 1980 when the DSM-III was introduced by the American Psychiatric Association (APA).2-5
The DSM-III balkanized the manic depression spectrum into either major depressive disorder or bipolar disorder. Consequently, individuals presenting with clinically significant affective disorders were categorized as either “unipolar” or “bipolar.” The intention of the DSM was positive insofar as there was a clinical need, amplified by the availability of treatments (e.g. lithium, tricyclic antidepressants), to differentiate individuals with current or past history of hypo/mania from those without.
During the past three decades, several cross-cultural, international, multi-site, phenomenological studies have provided convergent evidence that many individuals with “unipolar disorder” experience subthreshold hypomanic symptoms.3,6-9 Moreover, it is well established that depressive symptoms and episodes are the most enduring and disabling aspect of “bipolar disorder”. The observation that “unipolar disorder” could have hypomanic symptoms, but no past history of hypo/mania, created a conceptual, nosological, and subsequently therapeutic conundrum.
Also during the same epoch, separate lines of evidence have reported that the diagnosis of “bipolar disorder” had been increasing, most notably in North America and amongst younger adult populations.10 The so called “over-diagnosis” of “bipolar disorder” exists alongside separate lines of research indicating that “bipolar disorder” is under-diagnosed. In other words, a significant percentage of individuals with “bipolar disorder” often do not receive accurate and/or timely diagnoses, unnecessarily prolonging human suffering, resulting in progressive psychosocial decline, neurobiological progression of illness, and decreased responsiveness to pharmacological and psychosocial treatments. The conclusion that can be drawn is that misdiagnosis remains a critical problem amongst individuals with mood disorders and, as a consequence, guideline-concordant, measurement-based medical care is not provided.