Objective: There is much debate over whether borderline personality disorder (BPD) belongs to the bipolar spectrum. The diagnosis of bipolar disorder (BD) in BPD patients, and conversely, BPD in BD patients is common, indicating prevalent co-morbidity, as well as potential misdiagnosis in either group. BD and BPD are often indistinguishable given the core characteristics of emotional dysregulation and impulsivity that feature in both. However, it may be argued that the manifestation of these characteristics in the two groups is different, and that the symptoms are driven by distinct aetiological factors. The primary objective of this paper was to examine where potential areas of discrimination lie between BD and BPD.
Methods: A literature search was conducted using MEDLINE and PubMed databases to identify studies that have researched BD and BPD across the recognised domains of emotional dysregulation, impulsivity, childhood trauma, and their putative neurobiological substrates.
Results: Research comparing BD and BPD patients on self-report measures is limited, and no studies have examined their neurobiological underpinnings in the same design. One possible differentiating variable is childhood trauma which shapes the circumstances in which emotional dysregulation and impulsivity are triggered, the types of behaviours exhibited, and the frequency and duration of mood states. There is growing evidence that childhood trauma not only predisposes individuals to both disorders, but also modulates the clinical expression and course of bipolar illness, particularly rapid cycling BD, a form of bipolarity that resembles the clinical profile of BPD, yet presents quite distinctly from other BD subtypes.
Conclusions: This paper provides an overview of BD and BPD with respect to emotional dysregulation, impulsivity, childhood factors, and neurobiological substrates. Based on findings predominantly within the independent areas of BD and BPD, it tentatively provides an integrated behavioural, aetiological and neurobiological approach for investigating the question of whether BPD belongs to the bipolar spectrum.