This disorder was first listed in the Diagnostic and Statistical Manual of Mental Disorders, Third Edition (DSM-III) as shared paranoid disorder. In the next edition (DSM-IV), the term changed to shared psychotic disorder. In the latest edition, DSM-5, it was removed as a separate disease entity. It now is included in the section on other specified schizophrenia spectrum and other psychotic disorders. ICD-10 lists it as induced delusional disorder.
Shared psychotic disorder (folie à deux) is a rare disorder characterized by sharing a specific delusion among two or more people in a close relationship. The inducer (primary) who has a psychotic disorder with delusions influences another individual or more (induced, secondary) based on a delusional belief. It is commonly seen among two individuals, but in rare cases, can include larger groups. This activity outlines the presentation and management of shared psychotic disorder and highlights the role of the inter-professional team in improving the care of patients with this condition.
Jules Baillarger was the first to report this condition in 1860. During the 19th century, psychiatrists in Europe suggested different names. In France, it has been called “folie communiquee”(communicated psychosis) by Baillarger. In German psychiatry, it was named “Induziertes Irresein” by Lehman and Sharfetter. In 1877 Lasegue and Falret coined the term “folie à deux.” The French word “folie à deux” means madness shared by two. In the early 1940s, Gralnick, in his review of 103 cases of folie à deux, described four types of this disorder. He defined it as a psychiatric entity characterized by the transfer of delusions from one person to one or several others who have a close association with the primarily affected person.
The four types are as follows:
Folie imposee (imposed psychosis) – Described by Lasegue and Falret in 1877. The delusions are transferred from an individual with psychosis to an individual without psychosis in an intimate relationship. The delusions in the induced individual soon disappear once the two are separated.
Folie simultanee (simultaneous psychosis) – Described by Regis in 1880. Both partners share the psychosis simultaneously. They both have risk factors through long social interactions that predispose them to develop this condition. There are reports of sharing genetic risk factors among siblings.
Folie communiquée (communicated psychosis) – Described by Marandon de Montyel in 1881. This type is similar to folie imposee; however, the delusion in the secondary partner occurs after a long period of resistance. Also, the secondary partner will maintain the delusion even after separation from their partner.
Folie induite (induced psychosis) – Described by Lehmann in 1885. In this type, new delusions are assumed by an individual with psychosis who is being influenced by another individual with psychosis.
The exact cause of shared psychotic disorder is still unknown. However, certain risk factors associated with it include the following:
Length of the relationship: Numerous studies highlight the role of long relationship duration as an essential factor for developing this condition. It is crucial to understand that the attachment with the inducer plays a key role in adopting the delusion.
Nature of the relationship: The majority of cases reported are among family members. The commonest relationship is between married or common-law couples, and the second most common is between sisters.
Social isolation: Most reported cases indicate poor interaction with society. A confused individual can undergo influence under frightening conditions in the absence of social comparison. The information received by the secondary individual is in harmony with what the primary individual felt. The conviction of certain ideas will eventually prevail as the only solution to maintain a mutual relationship.
Personality disorder: Individuals usually show features of a personality disorder. The usual description for them is neurotic, introverted, and emotionally immature. Some case reports noticed features of premorbid personality disorders especially dependent (passive), schizoid, and schizotypal.
Untreated mental disorder in the primary: An untreated individual with chronic mental conditions can be a social risk factor of influence to the other partner or family. The commonest diagnosis in the primary is a delusional disorder followed by schizophrenia and affective disorder.
Cognitive impairment: It has been noted that the secondaries lack good judgment and intelligence.
Comorbidity of the secondary: An individual diagnosed with a mental disorder, including schizophrenia, bipolar affective disorder, depression, dementia, or intellectual disability, carries a risk of being influenced by another mentally ill person.
Life events: Stressful life events that affect the relationship can influence behavior in the individual to accept certain delusions or lessen their ability to resist their feelings or emotions. For example, a wife who has been suffering from delusions for several years starts accusing her husband, who has erectile dysfunction, of being in a relationship with a mistress or that the mistress is “stimulating him with sildenafil and narcotics.” He will eventually accept this belief because of his unstable, passive personality condition, as well as the serious situation from which he suffers.
Communication difficulties: Having difficulty sharing ideas can be a reason for preferring isolation. It is suggested that improving communication among dyad relationships through multiple-conjoint psychotherapy may help both partners understand the different points of view that will collapse in the presence of rigid, mindless thinking.
Age: Previous studies reported age differences, the older of the two in the relationship being an inducer and the younger being the induced. However, recent studies do not support this finding.
Gender: The disorder is more common among females, both as a primary or secondary.
This condition is important for some cases which are really enigmatic regarding disorders.
Al Saif F, Al Khalili Y. Shared Psychotic Disorder. [Updated 2023 Aug 28]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK541211/