Folie à deux is a psychiatric syndrome in which symptoms of a delusional belief are transmitted from one individual to another.
Margaret and her husband Michael, both aged 34 years, were discovered to be suffering from folie à deux when they were both found to be sharing similar persecutory delusions (Enoch and Ball, 2001). 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 (the tendency to catch and feel emotions that are similar to and influenced by those of others), which could be made independently in either case.
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 imposée is where a dominant person initially forms a delusional belief during a psychotic episode and imposes it on another person or persons with the assumption that the secondary person might not have become deluded if left to his or her own devices. If the parties are admitted to hospital separately, then the delusions in the person with the induced beliefs usually resolve without the need of medication.
- Folie simultanée describes either the situation where two people considered to suffer independently from psychosis influence the content of each other’s delusions so they become identical or strikingly similar, or one in which two people “morbidly predisposed” to delusional psychosis mutually trigger symptoms in each other.
In a well-publicised case in the United Kingdom, the condition was one of two possible diagnoses of a Swedish woman, Sabina Eriksson, who stabbed a man to death after he took her into his home, offering food and shelter. Eriksson had just been released from police custody following an incident on a motorway which grabbed news headlines. Caught on camera by a police documentary filmmaker, her twin sister ran into the path of an oncoming articulated lorry, sustaining severe injuries. Eriksson then immediately duplicated her twin’s actions by stepping into the path of an oncoming car; she survived the impact. The defence counsel in the ultimate murder trial claimed that Eriksson was a ‘secondary’ sufferer of folie à deux, influenced by the presence or perceived presence of her twin sister — the ‘primary’.