Genetic factors

Borderline personality disorder has been shown to be moderately heritable, with reported heritability estimates of 0.69 (Torgersen Reference Torgersen, Lygren and Oien2000). Contemporary literature (Sharp Reference Sharp and Kim2015) has highlighted the emergence of research that supports the complex biology–environment interactions that lend to the development of BPD over time.

Neurobiological mechanisms

Developmental theories

Linehan (Reference Linehan1993) postulated a biosocial theory that BPD is a disorder of emotion regulation, heightened emotional sensitivity and reactivity and slow return to the emotional baseline that results from interactions between individuals with biological vulnerabilities and an emotionally invalidating environment. Children exposed to such a developmental context have difficulty understanding, representing and regulating emotional experiences.

Haigh (Reference Haigh2013) describes five necessary primary emotional development experiences for healthy personality formation: attachment, containment, communication, inclusion and agency. A secure early attachment gives the developing infant a coherent experience of existence and is the experience through which loss and change can be tolerated. Containment offered to the infant by parental figures through the establishment and enforcement of boundaries that can hold distress within agreed, safe limits forms the basis of a safe world in which intolerable feelings and experiences can be survived. A further principle of healthy personality development involves open communication, whereby the child's distress can be put into words and acknowledged and mirrored contingently by caregivers. Inclusion occurs when individuals are held in mind by others who share their environment and where interdependence and social cohesion can emerge. An environment that promotes empowerment and the exercising of agency supports individuation and self-efficacy. Disruption in these fundamental requirements for emotional well-being and healthy personality development can occur when abuse, neglect, deprivation or loss occur in the early environment.

Attachment theory

There is a strong association between insecure attachment style and BPD, which is in line with the understanding that relationship instability is a core feature of the disorder (Agrawal Reference Agrawal, Gunderson and Holmes2004). Bowlby postulated that human infants demonstrate behavioural patterns such as proximity-seeking, smiling and clinging, which evoke reciprocal care-taking behaviour in adult caregivers such as touching, holding and soothing. These reciprocal behaviours promote the development of an emotional tie between infant and caregiver that constitutes attachment. It is through this attachment relationship that the infant develops an internal representation of self and other (Bowlby Reference Bowlby1973). A secure attachment allows the child to explore their environment safe in the knowledge that the caregiver is available when needed. A secure attachment supports the development of a stable, consistent, coherent self-image and a sense that one is worthy of love, along with an expectation that attachment figures will generally be responsive and accepting. Hence, early-life interactions with attachment figures inform a cognitive template that influences the experience of adult relationships later in life (Madigan Reference Madigan, Hawkins and Plamondon2015). An insecure attachment relationship compromises the capacity to develop such mental representations of mental states of the self and the ability to reflect on and correctly interpret those of others. Insecure adult attachment is associated with borderline traits, whereas secure attachment has a negative predicative value for personality disorders (MacDonald Reference MacDonald, Berlow and Thomas2013). In BPD, attachment anxiety negatively affects social cognition, including the ability to mentalise and to differentiate self from other (Beeney Reference Beeney, Stepp and Haliquist2015).

Mentalising theory

Fonagy (Reference Fonagy and Bateman2008) proposes that deficits in mentalising capacity are a core aspect of the psychopathology of BPD. Mentalising is the capacity to make sense of ourselves and of others in terms of mental states. It is suggested that parental emotional under-involvement with children impairs the acquisition of normal social cognitive capacities and undermines a person's experience of their own mind. People with BPD tend to misread their own minds and the minds of others when in intense interpersonal encounters, particularly when emotionally aroused.

Adverse events

Borderline personality disorder is associated with childhood trauma more than any other personality disorder (Yen Reference Yen, Shea and Battle2002), which in turn is related to BPD symptom severity (Zanarini Reference Zanarini, Frankenburg and Hennen2006). Although a history of abuse is common in people with BPD, childhood sexual abuse is neither necessary nor sufficient for the development of BPD, and other childhood experiences, particularly neglect by caregivers, represent significant risk factors (Zanarini Reference Zanarini, Williams and Lewis1997). Parental responsiveness following reports of abuse (believing the report, protecting the child and not expressing high levels of anger) may be a more important mediating factor than the pathogenic effects of the abuse itself in the long term (Horowitz Reference Horowitz, Widom and McLaughlin2001). It has also been postulated that the interaction of childhood trauma and temperamental traits, such as high neuroticism, particularly anxiety, could be associated with the severity of BPD (Martin-Blanco Reference Martin-Blanco, Ferrer and Soler2014b).

Emotional domain

Emotional dysregulation is a core feature of BPD. It is characterised by heightened emotional sensitivity, impairments in regulation of emotional responses and slow return to baseline from emotionally heightened states. This feature may be elucidated by asking the patient whether their emotions are liable to change quickly over the course of hours or days. Emotions may shift rapidly, particularly in response to interpersonal interactions, but the person may not be able to readily identify reasons for vacillations in emotional states. It is helpful to enquire how the patient manages their emotions and whether they regret their actions when their emotions have been intense. It is likely that their behaviour and responses are determined by their mood and emotional states.

Chronic feelings of emptiness or hollowness may also be endorsed that may relate to a variety of factors. Emptiness in BPD is closely related to feeling hopeless, lonely and isolated. Avoidance of engaging with activities and relationships that have previously engendered distress and disappointment and shutting out of emotions may contribute to feelings of emptiness and lack of fulfilment.

Difficulty controlling angry feelings, characterised by low frustration tolerance and a pattern of discharging angry feelings in verbal or physical aggression, may be described. Anger is typically inappropriately intense, with rapid escalation in emotional intensity and a slow return to the baseline state.

Interpersonal domain

A seminal feature of BPD is relational instability. In the assessment interview this aspect of the disorder can be elucidated directly by asking the patient about the quality of past and current relationships with their lovers, parents or significant family members. A potentially useful rule of thumb is that the more intimate the relationship, the more likely symptomology will be demonstrated. However, this disturbance is on a continuum and for more disturbed patients this will manifest in relationships with decreasing intimacy, including those with work colleagues or even casual encounters. Open questions such as ‘What are you like in relationships?’ are a good way to start. After receiving general information one can then move on to more specific questions about experiences of self and others such as ‘In the relationship with [x] do you find your thoughts and feelings about him/her changing between extremes?’, ‘[In the relationship] do you experience your feelings and thoughts about yourself changing between extremes?’. Typical symptomology in BPD includes unstable mental representations of self and other, which at the extremes may rapidly switch between love and hate. The individual may be exquisitely sensitive within relationships and it is useful to ask ‘Are you concerned about what others think of you?’, ‘Do you find yourself sensitive and easily hurt, offended or disappointed by others?’ and ‘Do you worry about others intentions?’ to draw out this feature. A history may be revealed that includes a high number of intimate relationships over the years, characterised by easily falling in love, rapid development of intimacy, followed by disillusionment and estrangement. Similarly, relationships with parents, family members and friends may be conflictual and oscillate between extremes of idealisation and denigration.

A fear of being abandoned or rejected in relationships may be endorsed. Worries about perceived impending separation and loss may engender expressions or acts of suicide or self-harm in an effort to prevent abandonment. Ultimately, however, such behaviour may have a destructive effect on the very relationship the person is trying to protect. On the other hand, individuals may pre-emptively end relationships that they perceive will inevitably lead to abandonment, thereby avoiding the experience of being rejected.

Behavioural domain

Impulsive behaviours may arise for people with BPD in an understandable attempt to manage difficult emotional experiences. A history of impulsivity may be examined with the questions ‘Do you tend to seek out novelty or risky experiences?’ and ‘Do you make plans in advance and consider the possible consequences?’. If a history of impulsivity is endorsed, enquire which behaviours are problematic: ‘Have you had problems with eating binges, spending sprees, drinking too much and verbal outbursts?’. Other impulsive behaviours may include gambling, reckless driving and sexual activity that is later regretted. Self-harm and suicide risk assessment are detailed under ‘Risk’ below.

Cognitive domain

Family history

A family history of mood and impulse control disorders is associated with the development of BPD (White Reference White, Gunderson and Zanarini2003). The nature and quality of relationships with significant attachment figures should be explored, keeping in mind the importance of secure attachment in the facilitation of the development of a sense of the self being lovable and others as supportive and dependable (Bowlby Reference Bowlby1982).

Educational and occupational history

Psychosocial functioning includes both vocational and social functioning. Regarding social functioning, assess for the presence of at least one emotionally sustaining relationship in which the patient has regular, close contact without elements of abuse or neglect. Typically, educational and occupational function will be impaired. Features of BPD, particularly impulsivity and affective instability, prospectively predict negative academic achievement (Bagge Reference Bagge, Nickell and Stepp2004). In clinical populations, people with BPD experience greater impairment in work, social relationships and leisure compared with those with depression. Establishing a patient's educational attainments and occupational history may illuminate scholastic underachievement, incapacity to sustain employment or a poor disciplinary record.

Forensic history

A diagnosis of personality disorder is associated with an increased risk of violence compared with the general population. In BPD, externalised aggression can result in intimate partner violence and various types of aggressive criminal behaviour (Sansone Reference Sansone and Sansone2012). Offenders with personality disorder have 2–3 times higher odds of being repeat offenders than mentally or non-mentally disordered offenders (Yu Reference Yu, Geddes and Fazel2012), and enquiry about contact with the law should therefore form part of the standard personality disorder history.

Self-harm

The nature, variety and frequency of self-harming behaviours should be examined during the assessment interview. Community-based studies show rates of self-harm of 10% in young people; the behaviour is frequently repetitive and more common in females than males (Hawton Reference Hawton, Saunders and O'Connor2012). Self-harm takes a variety of forms, including cutting, bruising, burning, biting and head-banging. People with BPD who engage in self-harm report more frequent, severe and diverse methods of self-injury, have greater diagnostic comorbidity, and report more severe depressive symptoms, suicidal ideation and emotional dysregulation compared with those without a diagnosis of BPD who self-harm (Turner Reference Turner, Dixon-Gordon and Austin2015). Self-harm behaviours can be conceptualised as coping efforts that serve to moderate emotional distress.

Sexual risk

People with BPD and comorbid substance misuse report higher rates of sexual risk behaviours, sexually transmitted diseases and commercial sex-work (Harned Reference Harned, Pantalone and Ward-Ciesielski2011). Women with BPD are at increased risk of teenage and unwanted pregnancies compared with women with Axis I disorders (De Genna Reference De Genna, Feske and Larkby2012). Women with BPD are more likely to be raped by a stranger and be coerced to have sex than women without BPD traits (Sansone Reference Sansone, Chu and Wiederman2011).

Suicide

Enquiry about past episodes of attempted suicide is imperative. Suicide attempts are common in BPD, with 60–70% attempting suicide at some point and rates of completed suicide of 10% (Oldham Reference Oldham2006). A history of attempted suicide is a risk factor for completed suicide (Brent Reference Brent2011). Non-suicidal self-injury and suicide attempts are considered to be phenomenologically distinct, distinguished largely by motivational factors, for example a suicide attempt is motivated by a wish to die but self-harm may be motivated by an attempt to regulate emotion or communicate distress. Several characteristics are associated with suicide attempts in this population, including major depressive disorder (Soloff Reference Soloff, Fabio and Kelly2005), substance use disorders (Black Reference Black, Blum and Pfohl2004) and affective instability (Yen Reference Yen, Pagano and Shea2005). Feelings of deep hopelessness are associated with severe suicide-related behaviours. Hopelessness differentiates more severe suicide attempters from non-attempters (Stanley Reference Stanley, Gameroff and Michalsen2011).

Dependent children

During the assessment it is important to identify the needs of any dependent children, since parental mental health difficulties have an impact on parenting and, subsequently, mental health outcomes of the child (Vostanis Reference Vostanis, Graves and Meltzer2006). A recent systematic review explored the nature of parenting in mothers with BPD and the impact of such difficulties on child outcomes (Petfield Reference Petfield, Startup and Droscher2015). The findings describe an association between maternal BPD and reduced sensitivity and increased intrusiveness in their interactions with their infant children. Mothers with BPD also found it more difficult to structure their child's activities, and their family environments had higher levels of disorganisation and hostility and lower levels of cohesion. Mothers with BPD reported feeling less competent and satisfied in the parenting role and, in turn, children appeared to experience interactions with their mother as less satisfying. Children of mothers with BPD experienced a range of difficulties, including problems with labelling and understanding emotions, more difficulties with friendships, increased negative attributional style and self-criticism. Increased levels of depression, suicidality and behavioural problems were shown in children of mothers with BPD.

Depression

Depression and BPD frequently co-occur and recurrence rates of depression are high in this population (Grilo Reference Grilo, Sanislow and Shea2005). A recent review (Yoshimatsu Reference Yoshimatsu and Palmer2014) examined the literature pertaining to major depressive disorder (MDD) in people with BPD. It is helpful to keep in mind that depression in BPD is experienced as subjectively more severe, is more related to interpersonal sensitivity, is more persistent than depression without BPD and tends not to improve until BPD improves. A 10-year study revealed that BPD and MDD have reciprocal negative effects on one another's time to remission and time to relapse (Gunderson Reference Gunderson, Stout and Shea2014).

Bipolar affective disorder

Phenomenological similarities between BPD and bipolar affective disorder confer a clinical challenge when distinguishing between these disorders and recognising their co-occurrence. This is important for a variety of reasons, including treatment, prognosis and suicide risk. Bipolar disorder with comorbid BPD has a more severe presentation of illness than bipolar disorder alone and BPD is highly predictive of a future diagnosis of bipolar disorder. Bipolar affective disorder and BPD are both associated with increased rates of suicide attempts, but their co-occurrence confers an additive risk, with the influence of BPD greater than that of bipolar affective disorder (Zimmerman Reference Zimmerman, Martinez and Young2014). Clinical studies suggest that people with BPD may be at increased risk of being misdiagnosed with bipolar disorder (Zimmerman Reference Zimmerman and Morgan2013). Diagnosis relies on endorsement of similar symptoms, which may result in diagnostic error, for example in distinguishing between the emotional instability consistent with BPD and the affective disturbance of bipolar disorder. However, the pattern of affective instability in BPD is characterised by transient changes in mood in response to interpersonal stressors, whereas bipolar disorder is associated with more sustained mood shifts (Paris Reference Paris and Black2015). Additionally, mood change in BPD is usually from euthymia to anger, which contrasts with the shift from depression to elation seen in bipolar disorder (Koenigsberg Reference Koenigsberg2010).

BPD with PTSD versus complex PTSD

Childhood trauma exposure increases the risk for development of a range of psychiatric diagnoses, including personality disorders, and there has been much debate on whether complex post-traumatic stress disorder (CPTSD) is distinguishable from BPD and comorbid PTSD or whether it is an amalgam of these disorders. ICD-11 has introduced an additional CPTSD construct comprising the three core features of PTSD (re-experiencing of the traumatic event(s) in the present, internal or external avoidance of traumatic reminders and hypervigilance to a sense of current threat) and additional disturbances in emotional dysregulation, self-concept and interpersonal relationships (World Health Organization 2018). CPTSD has been proposed as an alternative way to conceptualise the symptoms of adults exposed to prolonged and severe interpersonal trauma. Distinguishing between BPD and CPTSD – disorders that share characteristics in the domains of affect, identity and relational functioning – may present a diagnostic challenge, particularly since it is known that BPD is a disorder associated with traumatic experiences.

However, clinical differences are recognisable and will inform differences in treatment approach (Maercker Reference Maercker, Brewin and Bryant2013). Symptoms that are highly indicative of BPD rather than CPTSD include frantic efforts to avoid real or imagined abandonment, unstable and intense interpersonal relationships characterised by alternating between extremes of idealisation and devaluation, markedly and persistently unstable self-image or sense of self, impulsiveness and the presence of suicidal and self-injurious behaviour (Cloitre Reference Cloitre, Garvert and Weiss2014). Further details of these and other distinguishing symptoms are outlined in Table 1.

TABLE 1 Some features in the differential diagnosis of borderline personality disorder and complex post-traumatic stress disorder

It has been suggested that CPTSD reflects the developmental impact of childhood exposure to interpersonal trauma in the form of impaired emotion processing, dissociative experiences and attachment insecurity (van Dijke Reference van Dijke, Hopman and Ford2018). Although the overlapping features of CPTSD and BPD may reflect conceptual similarities between these conditions, it has been argued that CPTSD is neither a replacement diagnosis for BPD nor a subtype of BPD itself. Rather, it has been suggested that CPTSD captures the developmental effects of exposure to complex trauma and may better describe the group of people with a history of prolonged and severe trauma (such as childhood sexual abuse, torture or slavery) who develop fear-based symptoms related to traumatic stimuli (core PTSD symptoms) and trauma-related disturbances that are enduring and pervasive (emotion dysregulation along with altered relational and self-schemas) who have been previously ascribed a BPD diagnosis (Ford Reference Ford and Courtois2014).