ICD-11 features of a mixed mood state: Bold or simply old?

ICD Insight

The latest ‘news’ is that the International Classification of Diseases 11th Revision (ICD-11) is likely to be published in 2018 having been, by then, 11 years in the making. By this time, we will perhaps also have the Diagnostic and Statistical Manual of Mental Disorders (DSM)-5.1 and the iPhone 9, and Juno will have completed its mission exploring Jupiter. This is extraordinary. But will it prove worth the wait?

It is becoming increasingly apparent that our understanding of mood disorders as captured by current classificatory systems is rudimentary and that our zeal for reliability of diagnoses may have caused us to overlook several important aspects of the fabric of mood disorders.

First, by their very nature, it seems that mood disorders do not appear to lend themselves to categorical definition. Therefore, we need to return to dimensional concepts and to formulate emotional symptoms and syndromes along a spectrum (Ghaemi and Dalley, 2014). This dissonance between taxonomy and clinical reality is reflected empirically and explains the day-to-day difficulty clinicians face in identifying arbitrary cut-offs to make diagnoses (Malhi and Porter, 2014).

Second, the half-hearted attempts by DSM-5 to rectify this situation have possibly made matters worse. For example, DSM-IV mixed episodes have been supplanted in DSM-5 by a mixed features specifier, supposedly to lower the threshold for capturing mixed mood states (Malhi et al., 2015). Ironically, instead of providing clarity, this fundamental change in mixed states classification has further complicated the diagnostic process, and mixed episodes are no longer codable per se. Instead, the mixed features specifier allows for myriad combinations of symptoms to qualify as mixed. But the horse has bolted, and the key question now is whether ICD-11 will remedy matters.

So what needs to be done? Recent research clearly shows that any definition of mixed states must include core mixed features, such as distractibility, irritability and psychomotor agitation (Malhi et al., 2016). Furthermore, in order to make any future classification of mixed states meaningful and useful for clinicians, it needs to separate mixed mania (Renaires et al., 2015) and mixed depression and allow for both of these ‘states’ to be coded separately as episodes. This is critical because without this it is difficult to see how even basic epidemiological information regarding mixed states will be captured.

When put simply in straightforward language, these suggestions for improving the classification of mixed states seem reasonable and logical. However, in practice, this will require some bold decisions to be made by any ICD-11 committee overseeing these changes. First, they would need to depart from the template that DSM-5 has adopted. Second, they would need to create a definition that has a greater level of specificity than ICD definitions have hitherto employed, and do so on the basis of very modest evidence. The easiest position to adopt, for the sake of harmonization between the two taxonomies, would be to follow DSM-5. But this would make ICD-11 as redundant as DSM-5, and despite being a revision, it would offer nothing new. In other words, it would be instantly viewed as ‘old’.

Naturally, we hope that ICD adopts a bold position and not only completely revises the classification of mood disorders but also addresses the many other inconsistencies in our current classificatory systems.