Also called folie à deux, this occurs when one person in a relationship that has a delusion influences the other to develop that delusion. This can happen to groups too, referred to as folie à plusiers, and can be seen in cults. 

Shared psychotic disorder

There are different types of Delusional Disorder, depending on  the specific delusion the individual is experiencing:

- Delusional jealousy
- Bizarre
- Erotomania
- Grandiose
- Persecutory
- Somatic
- Mixed
- Thought broadcasting
- Thought insertion
- Unspecified


Types of Delusional Disorder

Certain populations are more vulnerable to this psychotic disorder:
- People who are deaf or hard of hearing
- People who are visually impaired
- People who face language barriers 
- Elderly People

Population at Risk for Delusion Disorder

A study found an association between the HLA-A*03 gene, delusional disorder, and paranoid schizophrenia. It is found that this gene alone, in combination with other HLA genes or other closely linked non-HLA genes, may lead to vulnerability to delusional disorder and paranoid schizophrenia.   

Genetic Association between Delusional Disorder and Paranoid Schizophrenia

Psychotherapy is typically used to treat delusional disorder. The treatment focuses on exploring possible biological and psychological problems and decreasing symptoms by helping the individual work toward reality. A therapist first establishes a trustful bond with the individual by expressing sympathy and accepting their delusions, a supportive response the individual is often not accustomed to from others. Subsequently, the therapist helps increase the individual’s self-confidence, challenges the delusional thought process, and addresses any underlying psychological problems. Cognitive-behavioral therapy and other solution-oriented therapies are particularly useful during this stage of treatment.

Psychotherapy for Delusional Disorder

Previously referred to as paranoid disorder, delusional disorder is characterized by an inability to recognize reality from false beliefs called delusions. It occurs more often in middle age or later in life. This disorder is diagnosed when someone holds one or more non-bizarre delusions as truth for a month or more. These delusions cannot be sourced from culture or other causes. Symptoms include irritability and hallucinations.  

University of Rochester

Syracuse University

Delusions are defined as beliefs that starkly contradict reality and are maintained with strong conviction, even when presented with conflicting evidence. Unlike merely odd beliefs, delusions are typically identifiable by their absurd nature.

Delusions

Psychotic disorders are severe mental illnesses characterized by thoughts, perceptions, and behaviors that are so impaired the individual cannot function normally and becomes disconnected from reality. This state of being disconnected from the world is known as psychosis. People with these disorders often lose contact with reality and may experience extreme symptoms like hallucinations and delusions. Schizophrenia is a primary example of a psychotic disorder.

Psychotic Disorders

The DSM-5-TR separates Schizophrenia and Other Psychotic Disorders into the following specific disorders and groups:

- Schizotypal (Personality Disorder)
- Delusional Disorder
- Brief Psychotic Disorder
- Schizophreniform Disorder
- Schizophrenia
- Schizoaffective Disorder
- Substance/Medication-Induced Psychotic Disorder
- Psychotic Disorder Due to Another Medical Condition
- Catatonia*
- Other Specified Schizophrenia Spectrum and Other Psychotic Disorder
- Unspecified Schizophrenia Spectrum and Other Psychotic Disorder


[DSM-5-TR] List of Schizophrenia Spectrum and Other Psychotic Disorders

Casarella, J. (2020, July 17). What Is a Psychotic Disorder? WebMD. https://www.webmd.com/schizophrenia/guide/mental-health-psychotic-disorders. 

Psychotic Disorders WebMD

Delusional Disorder: Treatments, Causes, Types &amp; Diagnosis. Cleveland Clinic. (2018). https://my.clevelandclinic.org/health/diseases/9599-delusional-disorder. 

Delusional Disorder Summary

Joseph, S. M., & Siddiqui, W. (2020, November 20). Delusional Disorder. StatPearls [Internet]. https://www.ncbi.nlm.nih.gov/books/NBK539855/. 

Delusional Disorder NCBI

Delusional Disorder

Types of delusions include:

- Erotomanic
- Grandiose
- Jealous
- Persecutory
- Somatic
- Paranoid
- Thought insertion
- Thought withdrawal

Types of Delusions

Paranoid delusions are a type of false belief centered on the conviction that other individuals or organizations are planning to cause harm to the person. For instance, an individual might believe that a family member is conspiring with a government agency to poison them, or that a neighbor is a hostile spy with malicious intent.

Paranoid Delusions

Grandiose delusions are false beliefs where an individual is convinced they possess exceptional abilities, exclusive knowledge, or are of immense importance. Examples include a person claiming to be a major historical figure like Jesus Christ, possessing ancient wisdom, or being a renowned philosopher.

Grandiose Delusions

Somatic delusions are false beliefs concerning one's body, involving the conviction that something highly unusual and often bizarre is occurring. A classic example is the belief that one's internal organs are being consumed by insects.

Somatic Delusions

Thought withdrawal is a type of delusion characterized by the firm belief that one's thoughts are being forcibly taken out of their mind by an external force.

Thought Withdrawal Delusions

Thought insertion is a type of delusion involving the conviction that thoughts have been placed into one's mind by an outside person or entity.

Thought Insertion Delusions

A delusion is a belief that is contrary to reality and is firmly held, even when presented with conflicting evidence. Based on this definition, which of the following scenarios provides the clearest example of a delusion?

Which of the following scenarios provides the clearest example of a delusion, as defined by a belief that is contrary to reality and firmly held despite contradictory evidence?

- Hallucinations
- Delusions
- Disorganized speech

Common Symptoms Across Psychotic Disorders

Empirically supported treatments for psychotic disorders. 

Psychotic Disorder Treatments

A sudden and temporary display of psychotic behavior, and can be triggered by extreme stress and trauma. This episode lasts less than a month, and is followed by complete remission, though future relapses are possible. 

Brief psychotic disorder

Schizophrenia is a severe psychological disorder that leads to a profound breakdown in an individual's ability to function, often necessitating hospitalization. It is characterized by significant disruptions in thought, perception, emotion, and behavior, including symptoms like hallucinations, delusions, incoherent thinking, bizarre actions, flat emotions, and a lack of motivation for basic activities. It is important to distinguish schizophrenia from dissociative identity disorder ('split personality'), as the term 'schizophrenia' refers to a 'splitting of psychic functions,' not a divided personality.

Schizophrenia

Psychotic Disorder References

Lynn, S. J., Polizzi, C., Merckelbach, H., Chiu, C.-D., Maxwell, R., van Heugten, D., &amp; Lilienfeld, S. O. (2022). Dissociation and dissociative disorders reconsidered: Beyond sociocognitive and trauma models toward a transtheoretical framework. Annual Review of Clinical Psychology, 18(1), 259–289. https://doi.org/10.1146/annurev-clinpsy-081219-102424 

Dissociation and Dissociative Disorders Reconsidered: Beyond Sociocognitive and Trauma Models Toward a Transtheoretical Framework

- Brief Psychiatric Rating Scale (BPRS)
- Abnormal Involuntary Movement Scale (AIMS)
- Extrapyramidal Symptom Rating Scale (ESRS)
- Dyskinesia Identification System Condensed User Scale (DISCUS)
- Clinician-Related Dimensions of Psychosis Symptom Severity (CRDPSS)

Current Scale to measure Psychotic Disorder Symptoms

Psychosis is a condition in which an individual becomes disconnected from the world that most people inhabit. It is the defining feature of a psychotic disorder, where a person's thoughts and perceptions are fundamentally impaired, leading to a loss of contact with reality.

Psychosis

A patient reports a firm belief that their neighbor is secretly a government agent who is replacing their thoughts with new ones via a hidden device. The patient cannot be persuaded otherwise, even when presented with contradictory evidence. This profound disconnection from a commonly shared sense of reality is the central feature of which category of mental illness?

A personality disorder characterized by: 
- Various oddities of thought, perception, speech, and behavior that are not severe enough to warrant a diagnosis of schizophrenia

Symptoms may include:
- Perceptual distortions
- Magical thinking
- Social isolation 
- Vague speech without incoherence
- Inadequate rapport with others due to aloofness or lack of feeling
- Symptoms not because of schizophrenia, other psychotic disorder, or ASD

Schizotypal Personality Disorder

Schizophreniform disorder is a psychotic disorder that affects action, thought, relationship with others, emotional expression, and reality perceived within one to six months lasting duration.

Schizophreniform Disorder

An uninterrupted illness featuring at some time a major depressive episode, manic episode, or mixed episode concurrently with characteristic symptoms of schizophrenia (e.g., delusions, hallucinations, disorganized speech, catatonic behavior) and, in the same period, delusions or hallucinations for at least 2 weeks in the absence of prominent mood symptoms. DSM–5 identifies the mood episodes only as either major depressive or manic and emphasizes that mood disturbances must be present for a majority of the time.

Schizoaffective Disorder

Substance/medication-induced psychotic disorder occurs when a specific substance (e.g., cocaine, dexamethasone) causes the delusions and/or hallucinations, or other schizophrenic-like symptoms. It is not to be confused with Substance/Medication-Induced Sleep Disorder.

Substance/Medication-Induced Psychotic Disorder

This condition is when hallucinations and delusions occur are physiologically caused by a separate medical condition. Psychosis appears outside states of delirium as well. The disorder significantly interferes with major areas of life.

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