Folie à deux and homicide: Literature review and study of a complex clinical case

Folie a Deux: Shared Psychotic Disorder in a Medical Unit

“…Based on the clinical interview, the pair's delusions appear to be persecutory in nature, and case reviews have found that persecution is the most common delusional theme in folie à deux [ 10 , 12 ]. The original definition of folie à deux determined that the delusions had some degree of likelihood “for it to be communicable” [ 2 , 7 ]. The patient and her mother provided limited details about their delusions, but crime and wiretapping were perhaps more likely than the delusions seen in psychotic disorders such as schizophrenia, including thought broadcasting, insertion, and withdrawal, Capgras delusions, or Truman delusions.…”

“…Thus, it is likely that, while suffering from these delusions, their functioning was at least marginally preserved without disorganization of their routines. This is commonly seen in folie à deux , reinforcing this diagnosis as opposed to another in which functioning and organization are more impaired, and lends itself to the difficulty of recognizing and learning more about this disorder [ 7 ]. Epidemiologically, in more than 90% of cases, the individuals experiencing a shared psychotic disorder belong to the same family with a high frequency of parent-child pairs, as seen here [ 7 , 10 – 12 ].…”

“…Throughout the years, additional terms to describe these phenomena were introduced, including “psychosis of association,” “double insanity,” “induced psychosis,” and “imposed psychosis” [ 7 ]. The central tenet in this disorder, regardless of the evolution of the definitions and subtypes, is the existence of delusional ideas amongst multiple people.…”

“…Some common themes and risk factors that have emerged in the study of folie à deux reflect the historical descriptions. These include a close, prolonged relationship between the inducer of the delusion and the recipient, a lack of another psychotic disorder explaining the development of the delusions, a delusion that is usually persecutory in nature, and maintenance of function without intellectual or affective disorganization in those afflicted [ 7 ]. The main risk factor for the development of folie à deux is extreme social isolation [ 9 ].…”

“…Patients with shared psychotic disorders are seldom identified as such, often do not meet criteria for involuntary psychiatric hospitalization, and go back to the environment that supports and reinforces the psychosis [ 7 ]. It is exceptionally rare to see a shared psychotic disorder in medically hospitalized patients, and even then, it may be an incidental finding as in the case described here.…”