Confusing borderline personality with severe bipolar illness

The paper by Yen et al. in this issue of the Acta Psychiatrica Scandinavica is an example of an increasingly obvious and disappointing fact: DSM-5 (and, in retrospect IV and III) are impeding us from conducting and interpreting meaningful research in psychiatry (1). The analysis presented simply accepts DSM assumptions and then claims that borderline personality worsens bipolar disorder. Yet the specific features that predict poor outcome are mood instability and impulsivity, which are quite non-specific for borderline personality disorder (BPD) and which are central to the whole concept of mania and bipolar disorder. As we will explain below, the DSM definition of BPD is such that it captures most patients with bipolar illness, specifically those with severe symptoms. So it becomes meaningless to say that ‘comorbid’ BPD ‘worsens’ bipolar illness, when the whole concept of BPD is defined to be equivalent to severe versions of bipolar illness. The observed data could reflect simply worsened features of bipolar illness (more impulsivity, more mood swings), and not something specific to borderline personality. (The authors acknowledge this limitation in parts of the manuscript, though not in the abstract; this critique may not be appreciated by many readers of the article, and others like it, hence this commentary.) This commentary provides a rationale for the above conclusion. The Course and Outcome of Bipolar Youth (COBY) study is an important contribution to our knowledge about childhood mood conditions. In this report, DSM-IV personality disorder definitions were assessed as predictors of outcome. This approach has been taken in many analyses, with wellcharacterized and prospectively followed samples. In general, it is found that DSM definitions of personality disorders, for example borderline, predict poor outcomes in DSM-defined mood syndromes (whether ‘major depressive disorder’, MDD, or bipolar illness) (2). A similar result is found in this paper for childhood bipolar illness. The usual conclusion is that BPD is a harmful ‘comorbidity’, predicting poor outcomes. Proponents of the BPD concept then advocate for more attention to its diagnosis and treatment (especially with psychotherapies, often psychoanalytically derived) (3). The authors here make the same claim, presented as straightforward interpretation of the data: ‘The number of BPD symptoms significantly predicted poor clinical course of BP, above and beyond BP characteristics. BPD severity adds significantly to the burden of BP illness and prospectively predicts a more chronic and severe course and outcome beyond BP characteristics’. This interpretation would have made sense in 1985, but stated baldly as it is in 2015, it fails to convince. The key assumption by the authors is that the concept of ‘comorbidity’ validly applies to this paper. The idea of comorbidity was proposed originally by the physician and epidemiologist Alvan Feinstein about 40 years ago to mean the simultaneous occurrence of two independent and separate diseases (4). Yet the DSM approach to BPD is such that it negates a valid concept of comorbidity. The diagnostic criteria given for BPD were developed by the DSM-III committee headed by Gunderson in the 1970s and have changed little under his leadership for the next 40 years in the 4th and 5th revisions (5). What does it mean to say that borderline symptoms predictor poor course ‘above and beyond’ bipolar symptoms? Readers should look at both DSM criteria sets. For borderline personality, it is perfectly feasible to meet diagnostic criteria simply based on standard, long-proven, well-accepted characteristics of the symptoms or consequences of bipolar illness. All you need is five of nine criteria, including: ‘affective instability’, ‘unstable interpersonal relationships’, anger, impulsivity (especially around sex and spending) and suicidal behaviour. The majority of patients with bipolar illness (whether type I or type II) will meet the above five criteria based on the symptoms or consequences of repeated manic/hypomanic and depressive episodes, not to mention the impact of mood temperaments of cyclothymia or hyperthymia in up to one-half of persons with bipolar illness. As we have argued previously (6), the most effective way to distinguish borderline personality from bipolar illness is on the four borderline criteria that are not included above: dissociative symptoms, chronic (not episodic) emptiness, identity disturbance and abandonment feelings. We would add the key importance of childhood sexual trauma, which the DSM framers continue to refuse to include in borderline criteria, despite a strong causal association. Further, we have reviewed data showing that recurrent parasuicidal behaviour, such as selfcutting, is more common in borderline personality than bipolar illness (6). This non-DSM manner of defining borderline personality and differentiating it from bipolar illness would present an opportunity for some useful data analyses that actually answer the question raised by the researchers: Does borderline personality worsen the course of bipolar illness? What could be said against the view-point presented in this commentary? One approach would be to say that it is not the role of researchers to either endorse or criticize DSM; rather researchers should take an agnostic approach, employing DSM criteria because they are the most widely used psychiatric nosological system. The problem with this approach is that it is unscientific: A scientific attitude is not agnostic; not all approaches are equally valid in science; some are proven more valid than others; and whatever is accepted by the majority is not thereby rendered more valid. This attitude is part of the problem in psychiatric research for the past two generations. We have simply refused to critique the DSM system in our research; instead, researchers claim it is not up to them to critique DSM. If not them, who will do it? Another response to this commentary could be that there is disagreement as to what constitutes ‘core’ criteria for BPD. Some argue for affective instability or interpersonal sensitivity as core criteria (7, 8). These perspectives conveniently ignore the history of BPD. As proposed by psychoanalytic thinkers like Kernberg and others (9, 10), although there were always differing views about the condition, borderline personality always involved patients who were not seen in any way as having manic-depressive illness. The original view of borderline