Delusional Disorder

Delusional disorder is a mental illness characterised by the presence of delusions—strong false beliefs despite superior evidence to the contrary—without prominent hallucinations, thought disorder, mood disorder, or significant flattening of affect.

Delusions can be bizarre or non-bizarre, with the latter involving situations that could occur in real life, such as being harmed or poisoned. Individuals with delusional disorder often maintain normal social and occupational functioning, although their preoccupation with delusional ideas can be disruptive.

Painting by Théodore Géricault portraying an old man with a grandiose delusion of power and military command. Grandiose delusions are common in delusional disorder.

Classification

The International Classification of Diseases (ICD) categorises delusional disorder as a mental and behavioural disorder. The Diagnostic and Statistical Manual of Mental Disorders (DSM) outlines seven subtypes based on delusional content:

• Erotomanic type (erotomania): Belief that another person, often a prominent figure, is in love with the individual.
• Grandiose type (megalomania): Delusion of inflated worth, power, knowledge, identity, or believing oneself to be a famous person.
• Jealous type: Belief that the individual's sexual partner is unfaithful.
• Persecutory type: Belief that the person or someone close to them is being malevolently treated.
• Somatic type: Belusions that the person has a physical defect or medical condition.
• Mixed type: Characteristics of more than one subtype, without a predominant theme.
• Unspecified type: Delusions that cannot be clearly characterised under other categories.

Signs and Symptoms

Delusional disorder manifests through persistent and forceful expression of beliefs despite evidence to the contrary. Indicators include:

1. Overemphasis on the delusional belief, altering the individual's life significantly.
2. Secretiveness or suspicion when questioned about the belief.
3. Humorlessness and oversensitivity.
4. Centrality of the belief, accepting unlikely scenarios unquestioningly.
5. Strong emotional reactions to contradictions, often with hostility.
6. Belief being out of keeping with the individual's social, cultural, and religious background.
7. Emotional over-investment in the belief, overshadowing other psychological elements.
8. Behaviour changes that are abnormal but understandable in light of the delusion.
9. Observations from others noting the uncharacteristic belief and behaviour.

Causes

The exact cause of delusional disorder is unknown, but genetic, biochemical, and environmental factors may play significant roles. Potential risk factors include family history, chronic stress, low socioeconomic status (SES), and substance abuse. Some people may have neurotransmitter imbalances, and there seems to be a familial component. Delusional disorder is on the same spectrum as schizophrenia but with fewer symptoms and less functional disability.

Diagnosis

Diagnosis involves ruling out other causes such as drug-induced conditions, dementia, infections, metabolic disorders, and endocrine disorders. Other psychiatric disorders must also be excluded. Key diagnostic tools include patient interviews, review of medical records, and input from immediate family. The Peters Delusion Inventory (PDI) is a psychological questionnaire used mainly in research to identify delusional thinking.

Treatment

Treatment of delusional disorder is challenging due to limited patient insight. Most patients are treated as out-patients, although hospitalisation may be necessary if there's a risk of harm. Individual psychotherapy is preferred over group therapy due to patient sensitivity and suspicion. Antipsychotics are not well-tested for delusional disorder and often have limited effect on core delusional beliefs but may help manage accompanying agitation.

Alternative treatments may include clomipramine for the somatic subtype and trimipramine for psychotic depression with delusional features. Psychotherapy, particularly cognitive therapy using empathy and Socratic questioning, is beneficial. Supportive therapy helps with treatment adherence and provides education, while social skills training can boost interpersonal competence. Insight-oriented therapy, though rarely indicated, has shown some success.

Epidemiology

Delusional disorders are uncommon, with a prevalence of about 24 to 30 cases per 100,000 people and 0.7 to 3.0 new cases per 100,000 annually. It accounts for 1–2% of admissions to inpatient mental health facilities. Delusional disorder tends to appear in middle to late adult life, more commonly in women and immigrants.

Criticism

In certain cases, delusions may turn out to be true beliefs, such as in delusional jealousy. Misdiagnoses can occur if psychiatrists lack the time or resources to verify claims, leading to the Martha Mitchell effect. Moreover, some normal beliefs share features with delusions, complicating the diagnosis. This has led to scepticism about the definition of delusion, as there is no universally accepted definition.

Self-assessment MCQs (single best answer)

Which of the following is NOT one of the seven subtypes of delusional disorder as outlined by the DSM?

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What is a common feature of individuals with delusional disorder?

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Which subtype of delusional disorder involves the belief that another person is in love with the individual?

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Which of the following is a common sign of delusional disorder?

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What is the prevalence of delusional disorder?

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Which of the following risk factors is NOT associated with delusional disorder?

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What is the primary diagnostic tool used to identify delusional thinking in research?

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Which treatment is NOT commonly used for delusional disorder?

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What is the Martha Mitchell effect?

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Which statement about delusional disorder is TRUE?

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