Mental Health

Delusional disorder

Delusional disorder is a primary psychotic disorder in which one or more thematically related delusions remain the dominant feature, typically for at least 3 months, while prominent schizophrenia symptoms, mood episodes, substances and medical causes have been excluded and functioning outside the delusional system is relatively preserved.

In a nutshell

Delusional disorder is an ICD-11 primary psychotic disorder dominated by one or more related delusions, typically persistent for at least 3 months, without a mood episode or prominent schizophrenia features. Diagnosis is specialist and requires targeted exclusion of medical, neurological, medication and substance causes, with risk and safeguarding assessment. NICE CG178 provides the UK psychosis framework: shared specialist antipsychotic trial when clinically indicated, CBT for psychosis and social support, baseline and ongoing physical-health monitoring, and regular review.

Classic presentation

A person has a months-long, high-conviction persecutory, jealous, erotomanic, grandiose or somatic belief and acts within that theme, while speech, affect and function outside it remain relatively preserved. Check for schizophrenia symptoms, mood episodes, medical or substance causes, and risk to the person or others.

Key points

ICD-11 describes delusional disorder as one or more related delusions, typically persisting for at least 3 months, without a depressive, manic or mixed episode.
The delusion is dominant but function outside its theme is relatively preserved; prominent persistent hallucinations, disorganisation or negative symptoms suggest another psychotic disorder.
A new delusion demands assessment for delirium, neurological or general medical disease, medicines, substances, mood disorder and schizophrenia-spectrum illness.
Do not argue with the belief or validate its explanation: acknowledge distress, build trust, assess risk and use shared goals.
When treatment is indicated, use a specialist, individual antipsychotic trial with the current BNF, CBT for psychosis and social support; evidence specific to delusional disorder is limited.
Before antipsychotics record weight, waist, pulse, blood pressure, glucose or HbA1c, lipids, prolactin, movement status, nutrition and activity; monitor systematically.
Morbid jealousy, persecutory beliefs, erotomania and somatic self-treatment can create serious risk to partners, alleged persecutors or the person themselves.

First-line investigation

Comprehensive specialist psychiatric, physical, neurological, substance and risk assessment with collateral information where possible; use targeted tests for red flags rather than routine imaging as a diagnostic shortcut.

Management

Assess safety and urgent causes

Assess threats, weapons, stalking, morbid jealousy, suicidal intent, self-treatment, neglect, safeguarding and immediate risk; involve crisis or emergency services and safeguarding or forensic colleagues when necessary.^3,5,8
New, fluctuating, late-onset or rapidly changing psychosis requires physical, neurological, medication and substance assessment; do not assume primary delusional disorder.^3,4

Formulate and engage

Use a calm, non-confrontational approach: acknowledge distress without endorsing the delusional explanation, obtain collateral information with consent, and agree a person-centred care and risk plan.^3,5

Offer specialist treatment when indicated

If persistent delusions cause distress, risk or meaningful impairment, discuss an individual specialist antipsychotic trial plus CBT for psychosis and social support; explain that direct evidence in delusional disorder is limited and treatment follows the NICE psychosis framework.^3,6,7
Before prescribing, record metabolic, cardiovascular, movement, prolactin and nutritional baselines; choose collaboratively, start low within licensed guidance and define the expected response and review plan.^3,7

Monitor, review and protect others

Monitor response, distress, function, adherence, movement effects, weight, waist, pulse, blood pressure, glucose or HbA1c and lipids at NICE intervals; review antipsychotic treatment at least annually.^3,7
Revisit diagnosis and adherence if benefit is inadequate, avoid routine combined antipsychotics, and maintain an explicit plan for relapse, contact with alleged persecutors, safeguarding and gradual discontinuation when appropriate.^3,6

Exam traps

Use the current ICD-11 duration of typically at least 3 months; do not import the older DSM-style 1-month rule without naming the classification.
Relative preservation outside the delusional theme does not make the belief reasonable or remove risk; assess actions, threats, stalking and self-treatment.
Persistent hallucinations, marked thought disorder, experiences of influence or prominent negative symptoms should trigger reassessment for schizophrenia-spectrum illness.
A late-onset, fluctuating or rapidly changing delusion is not primary delusional disorder until delirium, neurological disease, medicines and substances are considered.
NICE CG178 is a psychosis framework, not a delusional-disorder-specific drug guideline; discuss the limited direct evidence and avoid unsupported drug or dose claims.
Before antipsychotics, record metabolic, cardiovascular, movement, prolactin and nutritional baselines; monitor at NICE intervals.
Do not combine antipsychotics routinely or stop them abruptly; review benefit and harm, and use a shared gradual stopping plan when appropriate.

Key sources

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.