Diagnostic Features

The essential feature of Shared Psychotic Disorder (Folie a Deux) is a delusion that develops in an individual who is involved in a close relationship with another person (sometimes termed the "inducer" or "the primary case") who already has a Psychotic Disorder with prominent delusions (Criterion A). The individual comes to share the delusional beliefs of the primary case in whole or in part (Criterion B). The delusion is not better accounted for by another Psychotic Disorder (e.g., Schizophrenia) or a Mood Disorder With Psychotic Features and is not due to the direct physiological effects of a substance (e.g., amphetamine) or a general medical condition (e.g., brain tumor) (Criterion C). Schizophrenia is probably the most common diagnosis of the primary case, although other diagnoses may include Delusional Disorder or Mood Disorder With Psychotic Features.

The content of the shared delusional beliefs may be dependent on the diagnosis of the primary case and can include relatively bizarre delusions (e.g., that radiation is being transmitted into an apartment from a hostile foreign power, causing indigestion and diarrhea), mood-congruent delusions (e.g., that the primary case will soon receive a film contract for $2 million, allowing the family to purchase a much larger home with a swimming pool), or the nonbizarre delusions that are characteristic of Delusional Disorder (e.g., the FBI is tapping the family telephone and trailing family members when they go out). Usually the primary case in Shared Psychotic Disorder is dominant in the relationship and gradually imposes the delusional system on the more passive and initially healthy second person. Individuals who come to share delusional beliefs are often related by blood or marriage and have lived together for a long time, sometimes in relative social isolation. If the relationship with the primary case is interrupted, the delusional beliefs of the other individual usually diminish or disappear. Although most commonly seen in relationships of only two people, Shared Psychotic Disorder can occur among a larger number of individuals, especially in family situations in which the parent is the primary case and the children, sometimes to varying degrees, adopt the parent's delusional beliefs. Individuals with this disorder rarely seek treatment and usually are brought to clinical attention when the primary case receives treatment.

Associated Features and Disorders

Aside from the delusional beliefs, behavior is usually not otherwise odd or unusual in Shared Psychotic Disorder. Impairment is often less severe in the individual with Shared Psychotic Disorder than in the primary case.

Prevalence

Little systematic information about the prevalence of Shared Psychotic Disorder is available. This disorder is rare in clinical settings, although it has been argued that some cases go unrecognized. Limited evidence suggests that Shared Psychotic Disorder is somewhat more common in women than in men.

How Common Is Shared Psychotic Disorder?

The number of cases is unknown, but shared psychotic disorder is rarely seen in clinical settings, such as hospitals, outpatient clinics, or doctors' offices. In many cases, only one of the affected individuals seeks treatment, making a diagnosis of shared psychotic disorder difficult. As a result, many cases might go undetected.