Now I turn to look at this delusional type, as it involves a small social grouping between people who are often related to each other. It seems to involve processes where somehow a social group has become isolated, inward looking and the beliefs the individuals have, have a fixity to them that is resistant to treatment and often can only be broken upon separating the group members. Maintaining our social group has been a vital source of survival in the past, to the extent that strong efforts are made to keep the group together or to find another group. Would an investigation of the folie delusions provide some insight here? Are folie delusions another evolutionary way to maintain social groupings in the face of adversity?

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These types of delusions in essence involve group members sharing delusional beliefs. The number of people involved in the group is often two, but there are cases where three, four, or even five people can share the same delusional beliefs. These individuals are said to have exactly the same delusional content, where people are closely related, etc. From a clinical viewpoint, there seems to be five types (Kusum 2009, Soni 1974).

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• Folie impose – the delusional person ‘transmits’ the delusions to another.

• Folie simultanée – simultaneous psychosis in two vulnerable individuals, who have been associated with each other for a while. Separation is often ineffective here.

• Folie communiqué – delusions transferred after initial resistance and are maintained even on separation and both are often psychotic.

• Folie induite – delusions transferred to another psychotic individual.

• Folie a beaucoup was described by Brusell and involves a large number of people becoming delusional (Dewhurst 1957).

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Some authors feel that the secondary patient, the one who becomes delusional, must have some pre-existing condition that makes them more vulnerable, e.g. intellectual disabilities, dependent personality disorder. Others say that there needs to be a third person who does the ‘transmitting’ to the secondary patient. Sometimes it comes with other delusions and has been found in patients with schizophrenia, delusional disorder, psychotic depression and dementia. Still others have attracted a diagnosis of OCD, somatoform or dissociation (Kusum 2009). One case of an elderly lady with schizophrenia, who was taken in by a younger male of a kind nature. After a few months he began to follow the lady on her travels, e.g. collecting rubbish, holding water bottles for her. His self-care reduced and he became shabby. He developed paranoid delusions and gradually she became his only social contact and he even took her to work and sought her advice. Initially he shared her delusions but later he developed his own (Kusum 2009). A case of folie a trois, involving the grandmother, mother and the daughter, all of whom had developed schizophrenia. The second case described how when the delusional pair were rehoused, the delusions resurfaced against new neighbours. A secondary in a fourth case, drunk alcohol with the initial aim of allowing himself to believe his wife’s delusions. In the fifth case, the secondary was a 14 year old boy who was emotionally close to the primary, his mother. For the primary in the sixth case, the secondary was intellectually inferior to her. In the seventh case, the primary became psychotic, possibly in the context of underlying disease and she and the primary had two episodes of folie a deux over the years (Soni 1974). There was a case of folie a cinq, in five with evidence of borderline traits (Mirabzadeh 2007). It has been reported in recurrent depressive disorder, in this report the patient felt vermin was moving under her skin, which resolved with antidepressants and ECT (Mahler 2008). One case of shared paranoid delusions in the context of eating disorder found that the patient’s mother was the primary (Baweja 2013).

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Two reviews of cases of folie a deux have been carried out, from 1942 – 1993 and 1993 – 2005.  The mean ages of the primaries were 48.1 and 52.7 respectively and the secondary’s was 42.9 and 45.9 years respectively. The majority were female and over 90% were from the same family, with half being married, a quarter were sisters and about 70% involved the parent and child. The majority of cases displayed social isolation and were together for a mean of 72.98 months. Interestingly the primaries often had delusional disorder, schizophrenia and affective disorders, the secondary’s often were diagnosed with folie a deux (Arnone 2006). A review of patients from the Japanese literature found that there were 97 dominant patients, 151 submissive people, with about 75% of cases involving 2 people and over 90% involved family members. The relationships most often affected were those involving a mother and her child, married people, followed by siblings. The most common delusion was paranoia, followed by religious delusions (Kashiwase 1997). Another review did not find any age differences between the inducer and induced patients. Nor did they find a gender bias. About 30% of cases involved married people, siblings and parent-child relationships. Interestingly about 20% involved identical twins. Paranoid and then grandiose delusions were the commonest delusions found (Silveria 1995).

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In terms of physical disorders, it has been associated with lymphoedema, in one report the lady was living in an area rich in bancrofitian filariasis (Dreyer 2008). Many patients have been found to have physical conditions, but it was not possible to attribute some causal connection (Balducci 2017). There are reports in blind patients (Bidaki 2017), in SLE (Caribe 2013), dementia (Draper 1990), with stimulant use (Hill 2001), with multiple sclerosis (Malik 2000). One case involved deafness in the secondary patient (Soni 1974). It has been found with downs syndrome (Meakin 1987). There have been reports of folie a quatre (Kathiresan 2018), in a family with a history of Huntington’s chorea (Sims 1977).

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Delusional infestation has often been the subject of folie conditions. A 44 year old man had six years of itchiness without attracting a dermatological diagnosis. His wife, 16 and 18 year old daughters had similar problems, after initially resisting. It started after the wife developed delusions that the neighbours had inflicted a worm infestation on her and her family. She was diagnosed with paranoid disorder and her family with shared psychotic disorder (Daniel 2004). Another case involved a man, his wife and three children. The man had a diagnosis of paranoid schizophrenia, antisocial personality disorder and alcoholism. He had prevented his family from leaving the house and they too started to believe in his paranoid delusions. While the father was in hospital, the family recovered somewhat but the whole family were eventually lost to follow up (Srivastava 2010). Still another involved the delusional belief that outsiders had deliberately infested them in some way, with the mother dominating the husband and children (Daniel 2004; Sugahama 2000). Another family of 4 developed paranoid delusions after the primary, the daughter, developed delusions of infestation while in university (Katsigiannopoylos 2006). The coexistence of folie a deux and delusional parasitosis is about 5 to 15%. A 55 year old woman felt she was infested by bugs, and claimed to be seeing them all around her. Her son who helped her to look after an uncle and lived with her, felt that the bugs had transferred to him. They both had itchy sensations even though they stayed in hotels at times (Kim 2003). Two weeks after the primary developed it, her husband did also. She cleaned everywhere and used numerous chemicals to clean her house (Matthews 2005). case of shared paranoid delusions in the context of eating disorder found that the patient’s mother was the primary (Baweja 2013).

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The previous section mentioned regaining of social resources as a prelude to what we call delusional behaviour. There is evidence that the sharing of such beliefs is very common, with the groups closing ranks, providing protection, etc. A pivotal figure arises, proclaiming some future happening which results in people joining the cause (not all of whom are mentally ill), they come to believe in the same beliefs, which may then elicit benefits to the primary. Sometimes the primary is placed into a leadership position and some have speculated that this may help in dividing ancient social groups into smaller units to help protect society, other feel that it is the gaining of social benefit which is of importance (Hagen 1995, Stevens 2000).

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Typically the finding of folie a deux occurs between people who are socially close, such as husbands and wives (Ahmad 2009). When it comes to families and the folie conditions, the families may be isolated, with dependent and ambivalent relationships between them. They may experience crises more often, sometimes with violence. Within such a family network, there tends to be more stability, with one member being dominant to the other less. (Glassman 1987). The isolation though does not necessarily mean that people are physically isolated from people, it could simply be that they are isolated due to language or religious reasons (Majumder 2014).

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Occasionally there have been unfortunate cases whereby the presence of folie a deux leads to the death of a child (Kraya 1994). A mother with schizoaffective disorder with previous history of religious delusions and eventually her husband came to believe the same religious beliefs. They believed in demon possession, the sovereignty of god, that prayer will raise the dead, conspiracies theories and alternative medication, all of which were at odds with the church they attended (Rahman 2013). There has also been some reports where we see folie a deux by proxy, i.e. the inducer complains that the secondary has issues (Hussain 2018).

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Treatment of the folie Conditions involves separation of the pair often resolves the delusion in the secondary individual, though in folie communiqué this may not happen (Kusum 2009). ECT has been used successfully (Adler 1946).

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Univariate Analysis of Folie Dataset

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So I had collected case reports of patients with folie delusions and recorded information on various variables, e.g. age, gender, etc. Cases were found via Google Scholar, Pubmed and other resources and information was entered into a STATA datasheet. I did not have any specific hypothesis that I wanted to test, rather I just wanted to explore the data.

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Age – the mean age was 38.7 years, SD was 17.8. The youngest person in the group was aged 3 and the oldest was aged 89. The histogram of ages is shown below.