Folie à Deux

   Referring to the contagion of psychological symptoms, the term was coined in 1877 by Ernest-Charles Lasègue and Jules–Philippe-Joseph Falret (1824-1902) in an article in the Annales médico-psychologiques. "It has been said that mental illness is contagious and that the company of mental patients should not be considered exempt of danger for those who live in contact with them" (p. 322). There were, the authors allowed, certain circumstances in which this statement is not entirely false. When delusional patients succeeded in imposing their views on a second person, this latter person had several characteristics: "That he be of weak intelligence, more disposed to passive docility than to emancipation; second, that he lives in constant contact with the patient; thirdly, that he be enlisted [in the delusion] by the lure of some kind of personal gain. . . . One gives into the pressure of madness only if it causes one to glimpse the realising of a cherished dream" (p. 326).

   The German equivalent, "induced insanity"* (induziertes Irresein), was described by Georg Lehmann (1855–1918), then an assistant psychiatrist in the provincial asylum at Saargemünd in the former French province of Lorraine, in 1883 in the Archiv für Psychiatrie und Nervenkrankheiten. He concluded that the second person was usually constitutionally predisposed to mental illness. In 1894, Evariste Marandon de Montyel (1851–1908) at the Ville-Evrard asylum near Paris, in an article on "morbid mental contagion" in the Annales médico-psychologiques, identified three forms of the disorder: la folie communiquée (a concept that he took from Jules Baillarger [1809–1890] meaning approximately one person causing the symptoms of another, or induced insanity); la folie simultanée (two people exposed to the same cause who simultaneously become ill); and la folie imposée (a psychotic conveys his delusional ideas to someone who stands in a dependent relationship to him). DSM-III (1980) described folie à deux, with a nod to the French phrase, as "shared paranoid disorder": "The essential feature is a persecutory delusional system that develops as a result of a close relationship with another person who already has a disorder with persecutory delusions" (p. 197). In DSM-III-R (1987), this became "induced psychotic disorder"—with no mention of "folie à deux"—and in DSM-IV (1994) "shared psychotic disorder (folie à deux)."