One of the unwritten truths in psychiatry is that when we talk about personality we mean one. The Borderline. It is not that the others don’t exist, it is that they are not the ones that cause us problems. Clinically, it is a challenging diagnosis to make. Do not believe the textbooks that make it look easy… says me, quoting a textbook.

The term ‘borderline personality organisation’ was introduced by Otto Kernberg (1975) to refer to a consistent pattern of functioning and behaviour characterised by instability and reflecting a disturbed psychological self-organisation. Whatever the purported underlying psychological structures, the cluster of symptoms and behaviour associated with borderline personality were becoming more widely recognised, and included striking fluctuations from periods of confidence to times of absolute despair, markedly unstable self-image, rapid changes in mood, with fears of abandonment and rejection, and a strong tendency towards suicidal thinking and self-harm. Transient psychotic symptoms, including brief delusions and hallucinations, may also be present. The characteristics that now define borderline personality disorder were described by Gunderson and Kolb in 1978 and have since been incorporated into contemporary psychiatric classifications .

Either as a result of its position on the ‘border’ of other conditions, or as a result of conceptual confusion, borderline personality disorder is often diagnostically comorbid with depression and anxiety, eating disorders such as bulimia, post-traumatic stress disorder (PTSD), substance misuse disorders and bipolar disorder (with which it is also sometimes clinically confused). An overlap with psychotic disorders can also be considerable. In extreme cases people can experience both visual and auditory hallucinations and clear delusions, but these are usually brief and linked to times of extreme emotional instability, and thereby can be distinguished from the core symptoms of schizophrenia and other related disorders (Links et al., 1989).

The level of comorbidity is so great that it is uncommon to see an individual with ‘pure’ borderline personality disorder

Now for the paper. This is a latent class analysis: you need to read the main paper. It is attempting to find patterns between symptoms, and describe these clusters. The authors have used a large USA psychiatric survey. They note there are three clusters… and they co occur.

To our knowledge, this study is the first to jointly examine the latent structure of the symptoms of bipolar disorder and borderline personality disorder in a nationally representative sample. We found that a model with 3 positively correlated factors (ie, dimensions) provided an excellent fit for the latent structure of borderline personality disorder and bipolar disorder symptoms. These findings indicate that the dimensions underlying bipolar disorder and borderline personality disorder are not separate entities, but rather correlated constructs and, therefore, greater severity in one dimension increases the likelihood of having symptoms in the other dimensions. Furthermore, although the correlations between the factors were all positive, the correlation between the Depression and Mania factors was higher than the correlation between the Borderline Personality Disorder factor and the other 2 factors. This pattern of correlation is consistent with the existence of 3 syndromes, 2 of which (depression and mania/hypomania) often alternate or co-occur and constitute a unitary psychiatric entity (bipolar disorder) and a third syndrome (borderline personality disorder) that is often comorbid with bipolar disorder and shares important clinical manifestations with it, but represents an independent nosologic entity. Because our study was not limited to individuals meeting full diagnostic criteria for bipolar disorder or borderline personality disorder, its findings are also applicable to those meeting some, but not all, criteria for those disorders.
The relatively high correlations of the Borderline Personality Disorder factor with the Depression and Mania factors is consistent with results from studies that have documented a high degree of overlap in the prevalence, comorbidity, and symptoms of borderline personality disorder and bipolar disorder

This fits with what I see at work. Just because you have an emotionally unstable and vulnerable mood does not mean that you won’t get depressed or have bipolar: instead you may be more vulnerable.

And it explains why we often hedge our diagnoses, or flip between personality and mood. Both may be there. Both will need attention. The good news is that personalities can mature and change.

But that requires patience, talking therapy, and a psychodynamic level of understanding sufficient to tolerate the risk and concern that happens when you are dealing with impulsive, risky individuals. This, all too often, is absent from our managed and rationed mental illness systems.