Shared psychotic disorder (folie à deux) is a rare disorder characterized by sharing a delusion among two or more people in a close relationship. The inducer (primary) who has a psychotic disorder with delusions influences another nonpsychotic 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. For example, it can occur in a family and is called folie à famille.
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. more