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This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
Key points
- Enduring patterns of cognition, affect, interpersonal functioning, and impulse control deviating from norms — onset by adolescence/early adulthood
- Most clinically significant: emotionally unstable (borderline) PD — emotional dysregulation, unstable relationships, impulsivity, chronic emptiness, self-harm
- ICD-11 has moved to a dimensional model: severity (mild, moderate, severe) + trait domains (negative affectivity, detachment, dissociality, disinhibition, anankastia) ± borderline pattern
- First-line for borderline PD: psychological therapy — DBT (dialectical behaviour therapy) or MBT (mentalisation-based therapy)
- No medication is licensed for personality disorders — pharmacotherapy only for comorbid conditions or short-term crisis management
- Maintain a consistent, empathic, boundaried approach. Avoid splitting between services. Crisis plans are essential
Overview
Personality disorders are characterised by enduring, pervasive, and inflexible patterns of inner experience and behaviour that deviate markedly from cultural expectations, are present from adolescence or early adulthood, are stable over time, and lead to distress or functional impairment. ICD-11 has adopted a dimensional classification based on severity (mild, moderate, severe) and five trait domains (negative affectivity, detachment, dissociality, disinhibition, anankastia), with a specific qualifier for borderline pattern. Emotionally unstable (borderline) personality disorder (EUPD/BPD) is the most commonly encountered in clinical practice and is characterised by emotional dysregulation, unstable self-image, intense and unstable relationships, chronic emptiness, impulsivity, and recurrent self-harm or suicidal behaviour. Antisocial personality disorder is characterised by persistent disregard for social norms, deceitfulness, impulsivity, and lack of remorse.
Epidemiology
Personality disorders affect approximately 4–13% of the general population (depending on diagnostic criteria). Borderline PD has a prevalence of ~1–2% in the community and up to 20% in psychiatric inpatient settings. It is more commonly diagnosed in women, although this may reflect referral bias. Antisocial PD is more common in men (~3% vs 1%). Risk factors for borderline PD include childhood trauma (physical, sexual, emotional abuse), neglect, disorganised attachment, and genetic predisposition. Many people with personality disorders improve significantly over time, particularly borderline PD — prognosis is better than historically believed.
Clinical Features
Symptoms
Emotional dysregulation: rapid, intense mood shifts in response to interpersonal triggers
Unstable sense of self: identity disturbance, chronic emptiness, uncertainty about goals/values
Intense, unstable relationships: idealisation and devaluation ("splitting"), fear of abandonment
Impulsivity: reckless spending, binge eating, substance misuse, unsafe sex
Recurrent self-harm (cutting, overdose) or suicidal behaviour
Chronic feelings of emptiness, boredom
Transient stress-related paranoid ideation or dissociative symptoms
Intense anger, difficulty controlling anger — outbursts followed by guilt/shame
Signs
Scars from self-harm (forearms, thighs)
Emotional reactivity during consultation — rapid shifts between distress and calm
Difficulty maintaining consistent therapeutic relationship
Splitting behaviour between services/professionals (one idealised, another devalued)
Investigations
First-line
Clinical assessmentLongitudinal history from patient and informants. Assess pattern of difficulties across relationships, work, self-image, impulse control from adolescence onwards
Screening toolsStandardised Assessment of Personality (SAP) or SAPAS (abbreviated screen) in primary care — identifies likely personality disorder for further assessment
Risk assessmentSelf-harm, suicide risk, risk to others — create and review crisis/safety plan regularly
Second-line
Screen for comorbidityDepression (PHQ-9), anxiety (GAD-7), PTSD, eating disorders, substance misuse — very common comorbidity
Specialist
Specialist personality disorder assessmentStructured clinical interview (SCID-5-PD) or similar — diagnosis should be made by experienced clinician after ≥2 assessments
1
General principles
- Collaborative, empathic, consistent approach — maintain boundaries without being rigid
- Do NOT exclude from services because of self-harm or a diagnosis of personality disorder
- Develop a written crisis plan with the patient: what to do when distressed, who to contact, coping strategies
- Avoid "splitting" — ensure good communication between all teams involved in care
2
Psychological therapy (first-line for borderline PD)
- DBT (dialectical behaviour therapy): structured programme — individual therapy + skills group + phone coaching + team consultation. Usually 12 months
- MBT (mentalisation-based therapy): focuses on understanding own and others mental states. Usually 18 months
- CBT or schema-focused therapy — alternative options
- Sessions should be ≥weekly, minimum 3 months duration (NICE CG78)
3
Pharmacotherapy (limited evidence)
- No medication is licensed or recommended as primary treatment for personality disorder (NICE CG78)
- Do NOT use polypharmacy to manage individual symptoms of personality disorder
- Short-term medication may be considered for crisis management (e.g. low-dose antipsychotic or sedating antihistamine for ≤1 week)
- Treat comorbid conditions (depression, anxiety, PTSD) per their respective guidelines
4
Antisocial personality disorder (NICE CG77)
- Cognitive and behavioural interventions (group-based CBT, mentalisation-based programmes)
- No medication recommended for antisocial PD core traits
- Manage comorbid substance misuse, depression, ADHD as priority
- Risk management and multiagency working (including forensic services if appropriate)
Complications
- Suicide: ~10% lifetime risk in borderline PD — take all self-harm seriously
- Self-harm: Very common, recurrent — the most frequent reason for ED attendance
- Substance misuse: Common comorbidity — worsens impulsivity and emotional dysregulation
- Comorbid mental illness: Depression (~80%), anxiety, PTSD, eating disorders frequently coexist
- Relationship and occupational difficulties: Interpersonal instability, unemployment, social isolation
- Service disengagement: Inconsistent attendance, "revolving door" presentations — requires persistent, non-judgemental engagement
UKMLA Exam Tips
- 1Borderline PD key features: emotional dysregulation + fear of abandonment + unstable relationships + impulsivity + self-harm + chronic emptiness
- 2DBT is the most evidence-based therapy for borderline PD — four components: individual, skills group, phone coaching, team consultation
- 3No medication is first-line for personality disorders (NICE CG78). Treat comorbidities, not the PD itself, with drugs
- 4ICD-11 dimensional model: severity (mild/moderate/severe) + trait domains ± borderline pattern qualifier
- 5Personality disorder is NOT diagnosed during acute mental illness — pattern must be enduring and pervasive from adolescence
- 6Ego-syntonic: traits feel consistent with self (vs OCD which is ego-dystonic). Patients may not see the pattern as problematic
- 7Crisis plan: collaborative, written, regularly reviewed — reduces self-harm and ED attendance
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