Personality disorders (clusters A, B and C) !

Personality disorders are lasting, rigid ways of thinking, feeling and relating that cause distress or problems. There are ten types in three clusters.

Updated 2026-11-01

Structures involved

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What it is

An enduring, inflexible pattern of inner experience and behaviour that deviates markedly from cultural expectations, affects thinking, emotion, relationships and impulse control, begins by adolescence or early adulthood and causes distress or impairment. The DSM-5-TR groups ten types into three clusters.

Who gets it

Together they affect about 1 in 10 adults. Borderline personality disorder is common in psychiatric emergency and inpatient services, where it is linked to self-harm; antisocial personality disorder is more frequent in men and in prison populations. Diagnosis is usually not made before age 18 (antisocial requires age 18 and conduct disorder before 15).

Causes

Heritable temperament (impulsivity, emotional reactivity, anxiety)
Childhood abuse, neglect, invalidating environments or early loss
Cluster A shows a genetic link with schizophrenia
Interaction between biological vulnerability and adverse environment

Risk factors

Childhood trauma, especially sexual abuse (borderline)
Childhood conduct disorder (antisocial)
Family history of schizophrenia (cluster A) or of personality, mood or substance disorders
Unstable family environment and parental substance use

Pathophysiology

Personality reflects temperament shaped by experience. In borderline personality disorder, neuroimaging shows a hyper-reactive amygdala and weaker top-down control from the prefrontal and anterior cingulate cortex, matching intense, rapidly shifting emotions and impulsivity. In antisocial personality, reduced prefrontal function and blunted amygdala responses to fear and others' distress are described. These are group findings, not diagnostic tests.

Classification

Cluster A (odd, eccentric): paranoid, schizoid, schizotypal
Cluster B (dramatic, emotional, erratic): antisocial, borderline, histrionic, narcissistic
Cluster C (anxious, fearful): avoidant, dependent, obsessive-compulsive

Symptoms and signs

Cluster A: suspiciousness (paranoid), detachment and preference for solitude (schizoid), odd beliefs, magical thinking and eccentric appearance (schizotypal)
Borderline: unstable relationships and self-image, fear of abandonment, splitting, impulsivity, recurrent self-harm, chronic emptiness and intense anger
Antisocial: disregard for others' rights, deceit, aggression, irresponsibility and lack of remorse
Histrionic: attention-seeking and shallow emotion; narcissistic: grandiosity, need for admiration, lack of empathy
Cluster C: avoidance from fear of rejection (avoidant), need to be cared for (dependent), perfectionism and rigidity (obsessive-compulsive)

Diagnosis

Clinical: Diagnosis by a mental health professional from a longitudinal history, collateral information and DSM-5-TR criteria; the pattern must be pervasive and stable over time, not limited to episodes of another mental disorder or substance use. Suicide and violence risk assessment is part of every evaluation.
Tests: No laboratory test diagnoses a personality disorder. Toxicology screening when substance use is suspected; structured interviews or questionnaires may support the assessment.
Imaging: Not used for diagnosis; imaging only if a late change in personality suggests a brain lesion (e.g. frontal tumour or injury).

Differential diagnosis

Bipolar disorder (episodic mood changes lasting days, not lifelong instability)
Schizophrenia and delusional disorder (cluster A has no persistent psychosis)
Post-traumatic stress disorder
Substance use disorders
Personality change due to a medical condition (frontal lobe injury, tumour)

Goal of treatment

Reduce self-harm and crises, improve emotional regulation and relationships, and treat coexisting depression, anxiety or substance use, mainly through long-term psychotherapy with a consistent team.

Treatment

Conservative: Psychotherapy is the main treatment. For borderline: dialectical behaviour therapy (DBT), mentalisation-based therapy, schema therapy or transference-focused therapy. Cognitive behavioural therapy helps cluster C.
Medical: No drug is approved for personality disorders themselves. Medicines (SSRIs, mood stabilisers, low-dose antipsychotics) are used for specific symptoms or coexisting disorders, for limited periods, with attention to overdose risk.
Acute: Crisis care for suicidal behaviour: safety assessment, removal of means, and brief admission only when needed.
Follow-up: Nursing care sets clear, consistent limits, avoids being drawn into splitting among staff, and monitors suicide risk.

Complications

Suicide (borderline carries a high lifetime risk)
Depression, anxiety, eating and substance use disorders
Violence, legal problems and incarceration (antisocial)
Unemployment and relationship breakdown

Prognosis

Long-term but not unchangeable. Many people with borderline personality disorder improve markedly with time and specific psychotherapy, and impulsive behaviours often decline after age 40; antisocial behaviour also tends to lessen with age. Cluster A traits tend to be more stable.

Test yourself

Think of the answer, then tap the question to see it.

What are the three clusters of personality disorders and their general descriptors?

A: odd or eccentric; B: dramatic, emotional or erratic; C: anxious or fearful.

What is the psychotherapy with the strongest evidence for borderline personality disorder?

Dialectical behaviour therapy (DBT), which reduces self-harm and suicidal behaviour.

What two age conditions are required to diagnose antisocial personality disorder?

The person is at least 18 years old and had conduct disorder before age 15.

Which defence mechanism, seeing people as all good or all bad, is typical of borderline personality disorder?

Splitting.

Which personality disorder differs from schizophrenia mainly by lacking persistent psychosis but shows magical thinking and odd beliefs?

Schizotypal personality disorder (cluster A).

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: Personality Disorders (MedlinePlus, US National Library of Medicine, 2024).

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Representative model, for educational purposes only.

Frontal lobe highlighted on the Durgical 3D model