Last updated on:March 25th, 2022
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Personality disorders are deeply ingrained and enduring behavior patterns that manifest as inflexible responses to a broad range of personal and social situations. The importance of having a rigorous understanding of personality disorders lies in their tendency to impact healthcare-seeking behavior and provider-patient relationships. People with borderline personality disorder (BPD) typically suffer from pervasive emotional dysregulation (or affective instability), strained interpersonal relationships, disturbances in self-image, and a high rate of impulsivity. This characteristic phenotype arises from a combination of a genetic predisposition and early life trauma.
BPD is the most extensively studied personality disorder. It is common in both general and clinical populations—though more so in the latter due to associated high treatment-seeking behavior. While there is no gender difference in its prevalence, it is diagnosed more frequently in assigned females at birth. However, assigned males at birth diagnosed with BPD are found to suffer greater morbidity, including higher rates of impulsivity, comorbid psychiatric conditions, substance misuse, and suicidality.
BPD is strongly heritable; patients also frequently report traumatic life events such as physical or sexual abuse and emotional deprivation—specifically, environmental constraints on free emotional expression during childhood. This combination of genetic predisposition and trauma, especially early in life, is thought to manifest the characteristic phenotype of BPD—pervasive emotional dysregulation, interpersonal conflict, disturbance in self-image, and impulsivity including self-harm, via underlying neurobiological anomalies. In a vicious cycle, these experiences and behaviors enhance the patient's vulnerability to further trauma.
A central role of the hypothalamic-pituitary-adrenal (HPA) axis has been posited. Patients with BPD have been found to have higher baseline cortisol levels and impaired HPA feedback. Lower than normal peripheral oxytocin and raised testosterone have also been implicated. Volumetric neuroimaging studies have revealed bilateral reductions in grey matter volumes in the amygdala, hippocampus, and medial temporal lobe (MTL). Amygdala hyperactivity, particularly on the left side, has been associated with the aberrant processing of negative environmental stimuli, which can adversely impact emotional regulation but also presents a target for novel treatments.
In the American Psychiatry Association's Diagnostic and Statistical Manual of Mental Disorders (DSM-5), BPD is classified as a Cluster B personality disorder. There are four Cluster B personality disorders in total. These often coexist.
In the World Health Organization's International Classification of Diseases (ICD-10), BPD is classified under Emotionally Unstable Personality Disorder (EUPD). This has two variants: impulsive and borderline. Both often coexist.