Predominant polarity in bipolar disorders: refining or redefining diagnosis?

The major criticism that is usually posed against categorical diagnosis in psychiatry concerns their lack of theoretical basis with lack of biologic underpinning, poor specificity and alleged overinclusiveness. We do not wish to enter this controversial debate, but there is some agreement amongst clinicians and researchers that psychiatry badly needs more accurate and specific diagnostic categories. The inclusion of DSM course specifiers is thought to help refine diagnostic categories in order to make them more reliable and adapted to the almost endless clinical presentations of any psychiatric condition. Hence, a course specifier should define a clearly different subpopulation within a diagnostic boundary, provide some clinically relevant information and have therapeutic and prognostic implications. Unfortunately, many of the existing specifiers do not fulfil many of these criteria. In a review on DSM-IV modifiers performed to identify which changes should DSM-5 undertake, it became evident that most of the existing modifiers were not particularly evidence-based, did not clearly define any specific subgroup of individuals and/or would not have treatment and prognostic relevance (1). Specifically, some widely used specifiers such as postpartum episode (but not postpartum onset) failed to show therapeutic and prognostic implications (2) whilst others needed to be completely redefined as they ignored some clinical presentations. The last is the case of seasonal pattern, which until DSM-IV only took account of depressive – but not (hypo)manic – episodes, with little prognostic implications according to this extremely narrow definition (3). This was fortunately changed in DSM-5. Last, the vast majority of current specifiers are not longitudinal but actually cross-sectional, with few exceptions such as rapid cycling (4). Cross-sectional features may be sometimes helpful, but course specifiers have a plus in terms of predictive value. Indeed, there is a need to include longitudinal specifiers that inform the clinician about long-term course of illness and impact treatment choices and approach. One focus that received little attention in the development of DSM-5 is that many bipolar patients have a clear tendency towards one pole or another (mania/hypomania vs depression), a tendency that has been managed intuitively by the treating physicians for many years. However, in a similar manner that physicists aim at representing natural phenomena in mathematical formulations, physicians would ideally tend to better understand and make the best treatment choices for complex illness phenomena by operationalizing them. In fact, some attempts have been made to achieve some degree of operationalization of this tendency towards one pole or another. The first studies on this issue were performed by Jules Angst, who described clear groups of patients classified as ‘preponderantly’ manic (more manic and hypomanic episodes than depressive, lifetime) or depressed (more depressive episodes) or ‘nuclear’ (half and half) type in a long follow-up that exceeded 10 years (5). Angst works stressed the importance of repetitive binomial patterns (Md, Dm, dM, mD) rather than predominance of a polarity. Even then, his seminal studies pointed out at a close relationship between depressive preponderance and female gender, whilst males would be equally distributed amongst the three categories. More recently, two different proposals have been tested. The Barcelona proposal (6) is defined as at least two-thirds (2/3) of the total number of past episodes being from the same polarity. Hypomanic and manic episodes sum together against depressive episodes, and mixed episodes are not included in the definition. It has been tested in large samples in Spain, Italy and Brazil (6, 7). It has also been considered in some post hoc RCT studies (8) and was included in the ISBD Nomenclature Taskforce recommendations for the DSM5 (9) but unfortunately not included in the current version of DSM-5. A second, broader, proposal is the Harvard index that results from a quotient between the