Folie à deux (), also called shared psychosisBerrios, G. E., and I. S. Marková. 2015. "Shared Pathologies. Pp. 3–15 in Troublesome disguises: Managing challenging Disorders in Psychiatry (2nd ed.), edited by D. Bhugra and G. Malhi. London: Wiley. or shared delusional disorder (SDD), is a rare psychiatric syndrome in which symptoms of a delusional belief are "transmitted" from one individual to another.
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-IV – 297.3) and induced delusional disorder (ICD-10 – F24), although the research literature largely uses the original name. 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').
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. The 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" category.
Signs and symptoms 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 (imposed psychosis) 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'). Normally the latter, described as "un malade par reflet", does not suffer from a true psychosis. If the parties are admitted to hospital separately, the delusions in the person with the induced beliefs are typically abandoned. Folie simultanée (simultaneous psychosis) Either the situation where two people considered to independently experience 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. Due to the lack of a dominant partner, separation of patients might not improve the condition of either. Folie communiquée (communicated psychosis) Similar to folie imposée where the primary individual imposes the delusional belief on another. The latter assumes the same delusion after a period of time and develops their own delusional content not entirely derived from the initial primary's belief. Contrary to folie imposée, separation of the individuals will not improve the condition of either. Folie induite (induced psychosis) An uncommon sub-classification where the delusion of an individual with existing psychosis is enhanced by the delusional content of another person with psychosis. This may be seen in a hospital setting where both are patients.
Folie à deux and its more populous derivatives are psychiatric curiosities. The current Diagnostic and Statistical Manual of Mental Disorders states that a person cannot be diagnosed as being delusional if the belief in question is one "ordinarily accepted by other members of the person's culture or subculture". It is not clear at what point a belief considered to be delusional escapes from the folie à... diagnostic category and becomes legitimate because of the number of people holding it. When a large number of people may come to believe obviously false and potentially distressing things based purely on hearsay, these beliefs are not considered to be clinical delusions by the psychiatric profession, and are instead labelled as mass hysteria.
As with most psychological disorders, the extent and type of delusion varies, but the non-dominant person's delusional symptoms usually resemble those of the inducer. Prior to therapeutic interventions, the inducer typically does not realize that they are causing harm, but instead believe they are helping the second person to become aware of vital or otherwise notable information.
Type of delusions Psychology Today magazine defines delusions as "fixed beliefs that do not change, even when a person is presented with conflicting evidence." Types of delusion include:
Bizarre delusions Those which are clearly implausible and not understood by peers within the same culture, even those with psychological disorders; for example, if one thought that all of their organs had been taken out and replaced by someone else's while they were asleep without leaving any scar and without their waking up. It would be impossible to survive such a procedure, and even surgery involving transplantation of multiple organs would leave the person with severe pain, visible scars, etc. Non-bizarre delusions Common among those with personality disorders and are understood by people within the same culture. For example, unsubstantiated or unverifiable claims of being followed by the FBI in unmarked cars and watched via security cameras would be classified as a non-bizarre delusion; while it would be unlikely for the average person to experience such a predicament, it is possible, and therefore understood by those around them. Mood-congruent delusions These correspond to a person's emotions within a given timeframe, especially during an episode of mania or depression. For example, someone with this type of delusion may believe with certainty that they will win $1 million at the casino on a specific night, despite lacking any way to see the future or influence the probability of such an event. Similarly, someone in a depressive state may feel certain that their mother will get hit by lightning the next day, again in spite of having no means of predicting or controlling future events. Mood-neutral delusions These are unaffected by mood, and can be bizarre or non-bizarre; the formal definition provided by Mental Health Daily is "a false belief that isn't directly related to the person's emotional state." An example would be a person who is convinced that somebody has switched bodies with their neighbor, the belief persisting irrespective of changes in emotional status.
Biopsychosocial effects As with many psychiatric disorders, shared delusional disorder can negatively impact the psychological and social aspects of a person's wellbeing. Unresolved stress resulting from a delusional disorder will eventually contribute to or increase the risk of other negative health outcomes, such as cardiovascular disease, diabetes, obesity, immunological problems, and others. These health risks increase with the severity of the disease, especially if an affected person does not receive or comply with adequate treatment.
People with a delusional disorder have a significantly high risk of developing psychiatric comorbidities such as depression and anxiety. This may be attributable to a genetic pattern shared by 55% of SDD patients.
Shared delusional disorder can have a profoundly negative impact on a person's quality of life. Persons diagnosed with a mental health disorder commonly experience social isolation, which is detrimental to psychological health. This is especially problematic with SDD, as social isolation contributes to the onset of the disorder; in particular, relapse is likely if returning to an isolated living situation, in which shared delusions can be reinstated.
Causes While the exact causes of SDD are unknown, the main two contributors are stress and social isolation.
People who are socially isolated together tend to become dependent on those they are with, leading to an inducer becoming able to influence those around them. Additionally, people developing shared delusional disorder do not have others reminding them that their delusions are either impossible or unlikely. As a result, treatment for shared delusional disorder includes those affected be removed from the inducer.
Stress is also a factor, as it is a common factor in mental illness developing or worsening. The majority of people that develop shared delusional disorder are genetically predisposed to mental illness, but this predisposition alone is not enough to develop SDD. In other words, stress is a risk factor of this disorder. When stressed, an individual's adrenal gland releases the stress hormone cortisol into the body, increasing the brain's level of dopamine; this change can be linked to the development of a mental illness, such as a shared delusional disorder.
While there is no exact cause of shared psychosis, there are several factors that are contributors depending on different cultures and communities and taking into consideration the individual's circumstances, including their environmental changes and relationships.
Diagnosis Shared delusional disorder is often difficult to diagnose. Usually, the person with the condition does not seek out treatment, as they do not realize that their delusion is abnormal, as it comes from someone in a dominant position whom they trust. Furthermore, since their delusion comes on gradually and grows in strength over time, their doubt is slowly weakened during this time. Shared delusional disorder is diagnosed using the DSM-5, and according to this, the patient must meet three criteria: They must have a delusion that develops in the context of a close relationship with an individual exhibiting an already established delusion. The delusion must be very similar or even identical to the one already established in the primary case. The delusion cannot be better explained by any other psychological disorder, mood disorder with psychological features, as a direct result of physiological effects of substance abuse or any general medical condition.
Related phenomena Reports have stated that a phenomenon similar to folie à deux was induced by the military incapacitating agent BZ in the late 1960s. The chemical, also known as 3-quinuclidinyl benzilate, was being researched as a potential incapacitating agent, and its effects on mental state, including inducing a shared delusion, were observed in research studies.
Prevalence Shared delusional disorder is most commonly found in women with slightly above-average IQs, who are isolated from their family, and who are in relationships with a dominant person who has delusions. The majority of secondary cases (people who develop the shared delusion) also meet the criteria for dependent personality disorder, which is characterized by a pervasive fear that leads them to need constant reassurance, support, and guidance. Additionally, 55% of secondary cases had a relative with a psychological disorder that included delusions and, as a result, the secondary cases are usually susceptible to mental illness.
Treatment After diagnosis, the next step is to determine the proper course of treatment. The first step is to separate the formerly healthy person from the inducer, and see if the delusion goes away or lessens over time. If this is not enough to stop the delusions, there are two possible courses of action: medication or therapy. Therapy can be provided as both personal therapy or family therapy.
Medication