For other uses, see Folie à deux (disambiguation).
Folie à deux (/fɒˈli ə ˈduː/; French pronunciation: [fɔli a dø]; French for "madness of two"), or shared psychosis, is a psychiatric syndrome in which symptoms of a delusional belief and hallucinations are transmitted from one individual to another. The same syndrome shared by more than two people may be called folie à trois, folie à quatre, folie en famille or even folie à plusieurs ("madness of many"). Recent psychiatric classifications refer to the syndrome as shared psychotic disorder (DSM-IV) (297.3) and induced delusional disorder (F.24) in the ICD-10, although the research literature largely uses the original name. This disorder is not in the current DSM (DSM-V). The disorder was first conceptualized in 19th-century French psychiatry by Charles Lasègue and Jean-Pierre Falret and so also known as Lasègue-Falret Syndrome.
This syndrome is most commonly diagnosed when the two or more individuals concerned live in proximity and may be socially or physically isolated and have little interaction with other people.
Various sub-classifications of folie à deux have been proposed to describe how the delusional belief comes to be held by more than one person.
Folie à deux and its more populous cousins are in many ways a psychiatric curiosity. The current Diagnostic and Statistical Manual of Mental Disorders states that a person cannot be diagnosed as being delusional if the belief in question is one "ordinarily accepted by other members of the person's culture or subculture" (see entry for delusion). It is not clear at what point a belief considered to be delusional escapes from the folie à... diagnostic category and becomes legitimate because of the number of people holding it. When a large number of people may come to believe obviously false and potentially distressing things based purely on hearsay, these beliefs are not considered to be clinical delusions by the psychiatric profession and are labelled instead as mass hysteria.
In the case of twin sisters Ursula and Sabina Eriksson, Ursula ran into the path of an oncoming articulated lorry, sustaining severe injuries. Sabina then immediately duplicated her twin's actions by stepping into the path of an oncoming car; both sisters survived the incident. It was later claimed that Sabina Eriksson was a 'secondary' sufferer of folie à deux, influenced by the presence or perceived presence of her twin sister, Ursula – the 'primary'. Sabina later told an officer at the police station, "We say in Sweden that an accident rarely comes alone. Usually at least one more follows – maybe two." However, upon her release from hospital, Sabina behaved erratically before stabbing a man to death.
Another case involved Margaret and her husband Michael, both aged 34 years, who were discovered to be suffering from folie à deux when they were both found to be sharing similar persecutory delusions. They believed that certain persons were entering their house, spreading dust and fluff and "wearing down their shoes". Both had, in addition, other symptoms supporting a diagnosis of emotional contagion, which could be made independently in either case.
The 2011 independent film Apart depicts two lovers affected and diagnosed with induced delusional disorder, trying to uncover a mysterious and tragic past they share. In a 2011 interview, director Aaron Rottinghaus stated the film is based on research from actual case studies.
In 2016, a case involving a family of 5 in Australia made headlines when they abruptly fled their home and traveled more than 1,600 km because some of the family had become convinced someone was out to kill and rob them. No such evidence was found by the police.
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