Folie a Deux

Shared Psychotic Disorder
Feras Al Saif; Yasir Al Khalili.

Introduction
Shared psychotic disorder (Folie a deux) is an unusual mental disorder characterized by sharing a delusion among two or more people who are in a close relationship. The (inducer, primary) who has a psychotic disorder with delusions influences another individual or more (induced, secondary) with a specific belief. It commonly presents among two individuals, but in rare cases can include larger groups, i.e., family and called folie a famille.[1][2]

Baillarger was the first to report this condition in 1860. During the 19th century, psychiatrists in Europe suggested different names for this condition. In France, it has been called “folie communiquee”(communicated psychosis) by Baillarger. In German-speaking psychiatry, named “Induziertes Irresein” by Lehman and Sharfetter.  In 1877 Lasegue and Falret coined the term “folie a deux” and described this syndrome. The French word “folie à deux” means madness shared by two. The concept by itself highlighted that the delusional idea could be shared among two closely associated individuals or more. 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 and/or abnormal behavior from one person to one or several others who have a close association with the primarily affected patient. The types are the following:

1. Folie imposee (imposed psychosis) – Described by Lasegue and Falret in 1877. The delusions were transferred from one individual to another with the existence of an intimate relationship. These soon disappear once the two were separated.

2. Folie simultanee (simultaneous psychosis) – Described by Regis in 1880. Both partners shared the psychoses simultaneously. They both have risk factors through long social interactions that predispose to develop this condition. There are reports of sharing genetical risk factors among siblings.

3. Folie communiquée (communicated psychosis) – Described by Marandon de Montyel in 1881. This type is similar to type (1) however more resistance is applied to the delusions by the second partner. Finally, the second partner will adopt it even after separation.

4. Folie induite (induced psychosis) – Described by Lehmann in 1885. In this type, additional new delusions induced to the second partner by the first partner. Researchers noticed that an expansion of the delusions exists. This type would be present among two mentally ill individuals.

The first listing of this disorder in DSM-III was shared paranoid disorder, but in the later edition (DSM-IV) the term changed to shared psychotic disorder. However, in the latest edition, DSM-5, it was moved under other specified schizophrenia spectrum and other psychotic disorder. ICD-10 listed it as Induced delusional disorder.[2]

Ethology
The exact cause of shared psychotic disorder is still unknown. However, certain risk factors associated with it include:

• Length of a relationship: Numerous studies highlight the role of the long relationship duration as an essential factor for developing this condition. It is crucial to understand that the attachment with the primary case plays a key role in adopting the delusion.[3]
• Nature of the relationship: The majority of cases reported were among family members. The commonest relationship was between married or common-law couples and the second most common group was between sisters.[3]
• Social Isolation: Most cases reported poor interaction with society. An individual who is confused and perplexed can undergo influence under frightening conditions in the absence of social comparison. This information received by the secondary individual is in harmony with what the primary individual felt. The conviction to certain ideas will eventually prevail as the only solution to maintain a mutual relationship.[4]
• Personality disorder: Individuals usually show features of a personality defect. The usual description for them is as neurotic, introvert, and emotionally immature. Some case reports noticed features of premorbid personality disorders especially dependent(passive), schizoid and schizotypal.[5][6]
• Untreated Mental Disorder in the primary: An untreated individual with chronic mental conditions could 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.[3]
• Cognitive impairment: It has been noted that the secondaries lack good judgment and intelligence.[4]
• Comorbidity of the secondary: An individual diagnosed with a mental disorder, i.e., schizophrenia, bipolar affective disorder, depression, dementia or mental retardation carries a risk to be influenced by another mentally ill.[4]
• Life events: Stressful life events that affect the relationship could influence behavior in the individual to accept certain delusions or lessening the ability to resisting the feelings/emotions. An example could be a wife who is suffering from delusions for several years accusing her husband who has erectile dysfunction of being in a relationship with a mistress or that the mistress is “stimulating him with Viagra and narcotics.” He will eventually accept this belief taking into account the unstable passive personality condition, as well as the serious situation from which he suffers.[5]
• Communication difficulties: Having difficulties in sharing ideas could be a reason for preferring isolation. It is suggested that improving communication among dyad relationship through multiple-conjoint psychotherapy may help both partners understand the different point of views that will collapse in the presence of rigid mindless thinking.[7]
• Age: Previous studies reported age differences. The elderly being a dominant while the young being submissive, but recent studies do not support this finding.[2]
• Gender: It is more common among females to be part of this disorder, both as a primary or secondary.[2]

Epidemiology
The incidence and prevalence of this condition are difficult to estimate. However, some studies report 1.7 to 2.6% of psychiatric hospital admissions.[8] These figures could, however, be underestimated as it is under-diagnosed and often missed in clinical practice. Psychiatrists may treat the primary while not being aware that the delusions exist in others.[9] Some authors even argue that the disorder is not rare.[3]

Pathophysiology
The condition is usually chronic and both the dominant and submissive individual share the original delusions. The sharing of delusions occurs under unique circumstances. The shared delusions could be of any type. There are racial variations. The common types of delusions are persecutory, followed by grandeur. In Japanese communities, persecutory delusions were the commonest followed by religious delusions.[4][10] There could be other psychiatric features such as social withdrawal, hallucinations or suicidal thoughts.[11] The functionality is generally preserved compared with other disorders. There may be significant impairment in a particular aspect of life. When the delusions are not confronted, the person cannot maintain a normal lifestyle.

The concept of the dominance-submissive relationship derived from the psychodynamic theory. The role of the primary is rigid and possessing a dominant role in the relationship while the submissive being less intelligent, passive, less resilient to suggestions, isolated and physically handicapped. [6] Some authors even emphasized the existence of a reversal role between partners due to the complexity of the disorder.[7]

History and Physical
Cases are dependent on the type of delusion shared. One partner usually faces a problem in the society that involves the intervention of a psychiatrist. Often, this problem is supported or under the influence of the other partner. Both exhibit unrealistic fixed false beliefs which are unshakable. They might be paranoid, fearful and suspicious of a neighbor or someone in their community. One might seek mental assessment after risky behavior, unreal claims, or recent assault. The secondary partner could be mistakenly referred and usually discovers that other people within his/her social sphere share the same belief as the primary. There could be under-treated or even undiagnosed cases within the community that last for several years before being discovered. Sometimes partners who shared particular delusions could be admitted inside the hospital together because of risky behavior or assault to themselves or others.

• General description: The couples usually looking decent, well dressed and groomed.
• Behavior: Defensive attitude or angry behavior could result in the patient towards an interviewer who challenges his/her delusions.
• Speech: The speech is usually coherent and relevant.
• Mood/Affect: Mood is usually congruent with the delusion; a paranoid patient may be irritable, while a grandiose patient may be euphoric.
• Thought: The form of thought is usually directly goal oriented. The delusions are shared either entirely or partially, often not bizarre in content and are gradually systematically structured, overvaluing social/cultural/religious beyond the usual community norms or the presence of homicidal or suicidal plans.
• Perceptions: They are less likely to express abnormal perceptions unless there are predisposing factors. Sometimes the secondary is the only person who experiences a form of hallucinations.
• Orientation and Cognition: The patient usually oriented to time, place and person, unless being driven by his delusion. Memory and cognition are generally not affected.
• Risks: It is crucial to evaluate the patient for suicidal or homicidal ideations and plans. If there is a history of aggression with adverse outcome, then hospitalization should be considered.
• Insight and judgment: Most commonly patients and their partner have no insight regarding their mental illness. Judgment is assessable by questioning the history of past behavior and a future plan.[9][12][13]

Evaluation
As with any other psychiatric disorders, no specific labs are necessary for shared psychotic disorder.  Most of the investigations whether Imaging or laboratory tests should be considered to rule out any organic causes. A urine toxicology screen is vital to rule out any substance-induced conditions. If there are no medical/substance-induced condition, a full assessment should is next. It would be helpful to ask for collateral history about both partners from a third person. It is common to take history only from one of the partners because of strict social isolation situation; this would carry a great challenge for the psychiatrist. After taking a history, the psychiatrist should conduct a complete mental state examination. Collecting further details from other members of the family or friends should help in evaluating the case. The primary partner can be defensive and misleading leading to encapsulate the delusion; this will hide the symptoms for years unless s/he was acting on it.

Treatment / Management
Treatment should be tailored case by case. If there is an under-treated case, efforts should encourage increased adherence to the treatment plan. There have been suggestions that separation from the primary improves the condition significantly. After admission, the influence of the primary partner gradually disappears. It is worth noting, however, that recent data suggest that separation by itself could be insufficient or may aggravate the condition.[3][14] Treatment with medication for both partners whether alone (antipsychotics-antidepressant) or in combination (mood stabilizers/antipsychotics) and (antidepressants/antipsychotics) could improve the condition.[3] Those started on medications indicate that their condition is severe and likely to express residual symptoms. It is critical follow up with cases because of a possible alternative diagnosis. Psychotherapy could be offered to both partners either individually or as conjoined-psychotherapy.[7] ECT has also been an option.[3]

Differential Diagnosis
The differential diagnosis could be ruled out based on the history of the association between both partners. The onset of the condition usually precedes the onset of the shared delusions. The diagnosis of shared psychotic disorder should always only be made after ruling out any organic causes or substance induced.

• Schizophrenia/Schizoaffective: This could be differentiated if the case reported other findings that are not being influenced by the primary, i.e., hallucinations, disorganized speech, grossly disorganized or negative symptoms. In the case of schizoaffective, an affective component should be present.
• Mood Disorder with Psychotic features: This condition has a specific delusion which is mood congruent and not shared but expressed independently.

In case that the delusions do not disappear when the partners are separated, it is important to reassessment and consideration for an alternative diagnosis.

Prognosis
The prognosis of shared psychotic disorder is challenging to estimate, as it depends on multiple risk factors including the primary mental disorder and the secondary biopsychosocial predisposing factors. Theoretically, children are more likely to benefit from separation than adults. The adherence on management plan in both partners could provide a better outcome than being untreated. The assessment of nature or the duration of exposure to the delusion could provide clues on the outcomes of the disorder. Having premorbid personality features or predisposing risk factors could complicate the condition leading to consider an alternative diagnosis.[6]

Complications
The patients are not discovered easily due to lack of insight. They are usually referred after a complication, namely acting on such delusions that jeopardize their life or others. for example, a patient acts on his/her paranoid delusions through multiple accusations or commits an assault. Having delusions of grandeur or religious delusions could cause a hazard to others.[9]

Enhancing Healthcare Team Outcomes
Patients with shared psychotic disorder could be undiagnosed because only the primary partner gets registered for treatment in a classical presentation. The level of tolerance and harmony among the two patients both could add a significant challenge to the clinician to identify every partner’s role. Awareness is necessary regarding the nature of the dyad relationship dynamics and to manage it extensively. Most patients lack insight, which causes a substantial barrier to early discovery and management. The failure to adhere to treatment is an additional challenge to the clinician. A key aspect is to understand the impact of the delusions on both partner’s life. A board-certified psychiatric pharmacist should work with the team to select the best agents for optimal therapeutic results with minimal adverse effects. A holistic approach that assesses and manages the biopsychosocial factors should help for a better outcome. The psychotherapist, mental health nurse, and psychiatrist should continue to follow these patients as relapse is common due to noncompliance with treatment.

Shared psychotic disorder requires a comprehensive interprofessional team approach, that includes physicians, specialists, specialty-trained nurses, and pharmacists, working and communicating together in a team approach to lead to optimal treatment and outcomes. [Level V]

References

1. Srivastava A, Borkar HA. Folie a famille. Indian J Psychiatry. 2010 Jan;52(1):69-70. [PMC free article]
2. Shimizu M, Kubota Y, Toichi M, Baba H. Folie à deux and shared psychotic disorder. Curr Psychiatry Rep. 2007 Jun;9(3):200-5.
3. Arnone D, Patel A, Tan GM. The nosological significance of Folie à Deux: a review of the literature. Ann Gen Psychiatry. 2006 Aug 08;5:11. [PMC free article]
4. Silveira JM, Seeman MV. Shared psychotic disorder: a critical review of the literature. Can J Psychiatry. 1995 Sep;40(7):389-95.
5. Lew-Starowicz M. Shared psychotic disorder with sexual delusions. Arch Sex Behav. 2012 Dec;41(6):1515-20. [PMC free article]
6. Mentjox R, van Houten CA, Kooiman CG. Induced psychotic disorder: clinical aspects, theoretical considerations, and some guidelines for treatment. Compr Psychiatry. 1993 Mar-Apr;34(2):120-6.
7. Bankier RG. Role reversal in folie à deux. Can J Psychiatry. 1988 Apr;33(3):231-2.
8. Wehmeier P, Barth N, Remschmidt H. Induced delusional disorder. a review of the concept and an unusual case of folie à famille. Psychopathology. 2003 Jan-Feb;36(1):37-45.
9. Guivarch J, Piercecchi-Marti MD, Poinso F. Folie à deux and homicide: Literature review and study of a complex clinical case. Int J Law Psychiatry. 2018 Nov – Dec;61:30-39.
10. Kashiwase H, Kato M. Folie à deux in Japan — analysis of 97 cases in the Japanese literature. Acta Psychiatr Scand. 1997 Oct;96(4):231-4.
11. Vigo L, Ilzarbe D, Baeza I, Banerjea P, Kyriakopoulos M. Shared psychotic disorder in children and young people: a systematic review. Eur Child Adolesc Psychiatry. 2019 Dec;28(12):1555-1566.
12. Salih MA. Suicide pact in a setting of Folie à Deux. Br J Psychiatry. 1981 Jul;139:62-7.
13. Joshi KG, Frierson RL, Gunter TD. Shared psychotic disorder and criminal responsibility: a review and case report of folie à trois. J. Am. Acad. Psychiatry Law. 2006;34(4):511-7.
14. Talamo A, Vento A, Savoja V, Di Cosimo D, Lazanio S, Kotzalidis GD, Manfredi G, Girardi N, Tatarelli R. Folie à deux: double case-report of shared delusions with a fatal outcome. Clin Ter. 2011;162(1):45-9.

Research on Folie a Deux

Folie à deux—the psychosis of association; a review of 103 cases and the entire English literature, with case presentations.
Gralnick, A.
(1942). Folie à deux—the psychosis of association; a review of 103 cases and the entire English literature, with case presentations. Psychiatric Quarterly, 16, 230–263.
Abstract
This disorder is a psychiatric entity characterized by the transference of delusional ideas or abnormal behavior from one person to others who have been in close association with the primarily affected patient. It is classified according to 4 main types: imposed, simultaneous, communicated, and inducted. The most prevalent types, the imposed and the communicated, are differentiated by the degree to which the recipient elaborates and incorporates the delusional system of the primary agent into his own personality structure. In the 103 cases examined the order of frequency of combinations was: sister-sister (40 cases), husband-wife (26 cases), mother-child (24 cases), and brother-brother (11 cases). The imposed type was most prevalent (61 cases), followed by the communicated (24 cases). The main factors in these cases were length of association, dominance-submission, type of familial relationship, prepsychotic personality, sex and age, persecutory and religious delusions, and homosexual desires. Possible etiological factors are discussed. The disorder is considered as evidence for the importance of environmental factors.

Socio-Clinical Substrates of Folie à Deux
Som Datta Soni (a1) and Gerald Joseph Rockley (a1)
The British Journal of Psychiatry. Volume 125, Issue 586 September 1974, pp. 230-235Extract
Abstract
Folie à deux, the psychosis of association, has been defined as ‘the transference of delusional ideas and/or abnormal behaviour from one person to one or more individuals who have been in close association with the primary affected person’ (8). At least three conditions have been regarded as pre-requisite for its diagnosis: (a) definite evidence that the partners have been intimately associated, (b) identical content of the delusional ideas in both the patients, and (c) unequivocal evidence that the partners share, support and accept each other’s delusions.

Folie à Deux Revisited
Alistair Munro.
The Canadian Journal of Psychiatry. 1986, Vol 31, Issue 3.
Abstract
Folie à deux (shared paranoid disorder) is misleadingly defined in DSM-III. It is not an illness in itself, but a phenomenon associated with delusional psychiatric illnesses. There are two main types of folie à deux. An updated nomenclature is proposed.

Folie à deux
Michael H.Sacks
Comprehensive Psychiatry. Volume 29, Issue 3, May–June 1988, Pages 270-277
Abstract
A review of folie à deux or induced psychotic disorder (DSM-III-R) is provided. The author believes it to be a more frequent phenomenon than usually thought, especially when hospitalized patients are evaluated with their families. An argument is made for viewing it as a description of a relationship and possible influence between individuals who may have very different disease processes. This includes, in the secondary partner, a continuum from being very “impressionable” to having an autonomous and independent delusional disorder. A case report and suggestions for treatment are given.

Délire à deux: résultats d’une enquête auprès des psychiatres de l’Ouest.
(Shared delusions: Results of an investigation with Western psychiatrists.)
Boyer, Ch. and Degiovanni, A.
Annales Médico-Psychologiques, Vol 148(2), Feb, 1990. pp. 211-215.
Abstract:
Recalls the laws of J. Laseque and J. Falret (1877) regarding the formation of ‘folie a deux’ and compares them to the diagnostic criteria for shared paranoid disorder as outlined in Diagnostic and Statistical Manual of Mental Disorders (DSM-III). The results of a study conducted over a 3-yr period in various regions of France is reported that yielded a total of 65 cases. Clinical characteristics of this group that concur with those noted in the literature are described. It is noted that the habitual isolation cited in the literature is not characteristic of the group studies. It is concluded that the notion of induced delusion deserves to be reexamined in light of psychodynamic and systems theory and that further study should be devoted to understanding the role of sociocultural factors in shared delusional disorder.

Pseudocyesis associated with folie à deux.
Milner, Gabrielle L. and Hayes, Gwilym D.
The British Journal of Psychiatry, Vol 156, Mar, 1990. Special Issue: Cross-cultural psychiatry. pp. 438-440.
Abstract:
Presents the cases of a 27-yr-old 2nd-generation Jamaican woman and her 50-yr-old mother who both believed themselves to be pregnant when they were not. The daughter also exhibited auditory hallucinations, confusion, and thought disorder when admitted to psychiatric services. She was soon released at her own insistence but was later re-admitted and treated with oral neuroleptics. She maintained her delusions of pregnancy until she moved away from her mother. The mother insisted that she herself had been pregnant for 10 yrs and appeared to be experiencing acute paranoid psychosis at admission. She maintained her delusional ‘pregnancy’ and refused to engage in treatment.

Shared psychotic disorder: A critical review of the literature.
Silveira, José M. and Seeman, Mary V.
The Canadian Journal of Psychiatry / La Revue canadienne de psychiatrie, Vol 40(7), Sep, 1995. pp. 389-395.
Abstract:
Reviewed the literature to reassess the concept of shared psychotic disorder (SPD) using modern nosology and current biopsychosocial formulation. Data were analyzed on 61 case reports from 1942 to 1993 that met Diagnostic and Statistical Manual of Mental Disorders-IV (DSM-IV) criteria for SPD according to patient age, sex, nature and duration of the relationship with the ‘primary,’ and length of exposure to primary’s psychosis, family psychiatric history, comorbidity, social isolation of the dyad, presence of hallucinations, delusional type, and the diagnosis of the primary. Findings reveal: (1) male and females were affected with equal frequency; (2) there was equal prevalence in younger and older patients; (3) the majority of shared psychoses (90.2%) were equally distributed among married couples, siblings, and parent–child dyads; (4) comorbid dementia, depression, and mental retardation were common; (5) hallucinations were common; and (6) the majority of dyads (67.3%) were socially isolated. It is concluded that SPD probably occurs in premorbidly disposed individuals in the context of social isolation which is shared with a psychotic person.

Folie a deux in a forensic setting
Niazi A.F. Kraya and Colin Patrick
Australian and New Zealand Journal of Psychiatry. 1997, Vol. 31, Issue 6.
Abstract
Objective: This paper is written with the aim of presenting a series of cases of folie à deux, an unusual disorder, occurring in a forensic setting where all the victims suffered a fatal or near-fatal outcome. Similarities in the psychopathology in these cases are drawn and comments are made about their outcome in court. The paper is also written to draw attention to the potential risks involved in this type of case and to accent patterns in psychopathology and in legal outcomes.

Clinical picture: Five folie à dew cases are described. All are well known to one of the authors (NK), who has treated them at some stage of their illness, provided medico legal reports for the trial of cases 3, 4 and 5, and provided expert witness testimony in the trial of case 3. All case notes and other relevant documents were studied in detail and a brief summary is provided for each case.

Outcome: The cases appear to conform with the description of folie a deux given in the literature and consist of husband and wife (three cases), mother and daughter (one case) and twin brothers (one case). None of these cases had had any past psychiatric or criminal history, yet all the victims suffered a fatal or near fatal outcome. Additionally, all had shared religious delusions in one form or another.

Conclusions: Folie a deux cases with shared religious delusions can be a very high risk and could be potentially fatal in a family setting. The authors also highlight the difficulties inherent in a forensic system restricted to McNaughton rules, particularly when a person is on trial having committed, or being alleged to have committed, a serious offence, and who is found to be suffering from a psychotic illness.

Folie a deux in bipolar affective disorder: a case report
Anish S Patel  Danilo Arnone  William Ryan
Bipolar disorders: An international journal of psychiatry and neurosciences. April 2004, Vol. 6, Issue 2.
Abstract
Background: The syndrome of folie a deux is uncommon and often described in the context of schizophrenia. We report a case of induced delusional disorder associated with bipolar affective disorder (BAD).

Case report: We present a case of monozygotic twins in their late 60s with an unusually close relation with one another and relative isolation from other people. Both twins have been diagnosed as suffering from BAD and relapsed into mania with psychotic symptoms. During their hospital stay they exhibited features consistent with folie a deux. Separation caused disappearance of the phenomenon whilst the affective disorder persisted.

Conclusion: This case highlights the unusual and rare phenomenon of folie a deux occurring in the context of BAD. It also suggests current difficulty in defining folie a deux as an entity according to current diagnostic criteria.

The nosological significance of Folie à Deux: A review of the literature.
Arnone, Danilo, et. al.
Annals of General Psychiatry, Vol 5, Aug, 2006. ArtID: 11
Abstract:
Background: Folie à Deux is a rare syndrome that has attracted much clinical attention. There is increasing doubt over the essence of the condition and the validity of the original description, such that it remains an elusive entity difficult to define. Method: We conducted a systematic review of the literature of all cases reporting the phenomenon of Folie à Deux, from the years 1993-2005. Results: 64 cases were identified of which 42 met the inclusion criteria. The diagnoses in the primary and secondary were more heterogeneous than current diagnostic criteria suggest. There exists a high degree of similarity between the primary and secondary in terms of susceptibility to psychiatric illness, family and past psychiatric history, than previously thought. Conclusion: Folie à Deux can occur in many situations outside the confines of the current classification systems and is not as rare as believed, and should alert the clinician to unrecognized psychiatric problems in the secondary.

Folie à Deux and shared psychotic disorder
Mitsue Shimizu, Yasutaka Kubota, Motomi Toichi, Hisamitsu Baba
Current Psychiatry Reports. June 2007, Vol 9, Issue 3, pp 200-205.
Abstract
Folie à deux (FAD) was first described in 19th century France. Since then, the concept has been elaborated, and several subtypes of FAD have been successively reported in France. In contrast, studies in German-speaking psychiatry mainly focused on the conceptual boundary between reactive/endogenous psychosis and etiological hypothesis (ie, psychogenesis vs genetic predisposition). In North America, Gralnick wrote a seminal review and redefined four subtypes of FAD by adopting the European classical concepts. More recently, “shared psychotic disorder” in DSM or “induced delusional disorder” in ICD-10 was branched off from FAD. However, several classical subcategories of FAD were not included in these recent definitions, the nosological significance of which should not be underestimated. We examined demographic data of FAD case reports published from the 19th to the 21st century and found that some of the earlier hypotheses, such as females being more susceptible, older and more intelligent individuals being more likely to be inducers, and sister-sister pairs being the most common relationship, were not supported. The controversial issue of the etiology of FAD—association of subjects or genetically driven psychosis—was re-examined in light of recent studies.

Folie à deux and the courts.
Newman, William J. and Harbit, Melissa A.
Journal of the American Academy of Psychiatry and the Law, Vol 38(3), Sep, 2010. pp. 369-375.
Abstract:
Folie à deux is a condition that presents distinct challenges in the legal system. The authors searched the LexisNexis database for cases involving folie à deuxand provide a review of criminal and civil case law involving individuals with the diagnosis. The case surrounding Elizabeth Smart’s abduction from her Utah home is highlighted. Folie à deux is a formally recognized mental disorder, although it is intrinsically different from most other primary psychiatric conditions. It can cause considerable confusion among mental health experts and legal professionals alike. It is difficult to make a reliable diagnosis of a condition that is, to date, not well validated. The authors discuss possible directions for future research and suggest methods for examining evaluees with suspected folie à deux.

La folie à deux (ou folie communiquée).
Lasègue, Ernest Charles; Falret, Jules.
Dialogues in Philosophy, Mental & Neuro Sciences . Dec2016, Vol. 9 Issue 2, p62-68. 7p.
Abstract
Clinical cases of shared delusion (communicated psychosis) are presented and theoretically discussed for the first time. First, it is clearly stated that usually madness is not contagious, so the reasons explaining cases of interpersonal communication deserve thorough analysis. The authors describe the communication from, respectively, an adult to a child, an adult to an older person, and an older person to an adult. In all cases there are basic commonalities, i.e. the active person is really delusional but his/her delusion is plausible, otherwise delusional sharing would be harder; the receiving person is of weaker intelligence or (as in the case of children) highly suggestionable; both individuals live in close contact, in the same environment and for a long period. It is noteworthy that even in this paper Lasègue shows a particular sensibility for relational issues that are evident in the analysis of cases and in the therapeutic approach.