Folie à deux

Folie à deux (French- 'folly of two', or 'madness [shared] by two'), additionally known as shared psychosis or shared delusional disorder (SDD), is a rare psychiatric syndrome in which symptoms of a delusional belief, and sometimes hallucinations, are transmitted from one individual to another. The same syndrome shared by more than two people may be called folie à trois ('three') or quatre ('four'); and further, folie en famille ('family madness') or even folie à plusieurs ('madness of several'). The disorder, first conceptualized in 19th-century French psychiatry by Charles Lasègue and Jules Falret, is also known as Lasègue–Falret syndrome. Recent psychiatric classifications refer to the syndrome as shared psychotic disorder (DSM-4 – 297.3) and induced delusional disorder (ICD-10 – F24), although the research literature largely uses the original name. This disorder is not in the current, fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), which considers the criteria to be insufficient or inadequate. DSM-5 does not consider Shared Psychotic Disorder (Folie à Deux) as a separate entity; rather, the physician should classify it as "Delusional Disorder" or in the "Other Specified Schizophrenia Spectrum and Other Psychotic Disorder". This syndrome is most commonly diagnosed when the two or more individuals of concern live in proximity, 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 Where a dominant person (known as the 'primary', 'inducer', or 'principal') initially forms a delusional belief during a psychotic episode and imposes it on another person or persons (the 'secondary', 'acceptor', or 'associate') with the assumption that the secondary person might not have become deluded if left to their 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.