Folie À Deux

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Folie à deux ('madness for two'), also known as shared psychosis or shared delusional disorder (SDD), is a 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 was first conceptualized in 19th-century French psychiatry by Charles Lasègue and Jean-Pierre Falret and 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 DSM (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, but rather, the physician should classify it as “Delusional Disorder” or in the “Other Specified Schizophrenia Spectrum and Other Psychotic Disorder”.

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 is 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 his or her 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.
Folie simultanée describes either the situation where two people considered to suffer independently from 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.

Folie à deux and its more populous derivatives are in many ways a psychiatric curiosity. 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 labelled instead 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 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 are 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 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 are not affected 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.

Persons 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 because 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 inducers influence on those around them. Additionally, people developing shared delusional disorder do not have others reminding them that their delusions are either impossible or unlikely. Because of this, treatment for shared delusional disorder includes those affected be removed from the inducer.

Stress is also a factor because it triggers mental illness. The majority of people that develop shared delusional disorder are genetically predisposed to mental illness, but this predisposition is not enough to develop a mental disorder. However, stress can increase the risk of this disorder. When stressed, an individuals 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.

Diagnosis

Shared delusional disorder is difficult to diagnose because usually, the afflicted person does not seek out treatment because they do not realize that their delusion is abnormal as it comes from someone in a dominant position who 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 person afflicted must meet three criteria:

They must have a delusion that develops in the context of a close relationship with an individual with an already established delusion.
The delusion must be very similar or even identical to the one already established one that the primary case has.
The delusion cannot be better explained by any other psychological disorder, mood disorder with psychological features, 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.

Prevalence

Shared delusional disorder is most commonly found in women with slightly above-average IQs who are isolated from their family, and 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 a person has been diagnosed, 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 which is then broken down into personal therapy and/or family therapy.

With treatment, the delusions and therefore the disease will eventually lessen so much so that it will practically disappear in most cases. However left untreated it can become chronic and lead to anxiety, depression, aggressive behavior and further social isolation. Unfortunately there are not many statistics about the prognosis of shared delusional disorder as it is a rare disease and it is expected that the majority of cases go unreported; however, with treatment, the prognosis is very good.

Medication

If the separation alone is not working, antipsychotics are often prescribed for a short time to prevent the delusions. Antipsychotics are medications that reduce or relieve symptoms of psychosis such as delusions or hallucinations (seeing or hearing something that is not there). Other uses of antipsychotics include stabilizing moods for people with mood swings and mood disorders ( i.e. in bipolar patients), reducing anxiety in anxiety disorders and lessening tics in people with Tourettes. Antipsychotics do not cure psychosis but they do help reduce the symptoms and when paired with therapy, the afflicted person has the best chance of recovering. While antipsychotics are powerful, and often effective, they do have side effects such as inducing involuntary movements and should only be taken if absolutely required and under the supervision of a psychiatrist.

Therapy

The two most common forms of therapy for people suffering from shared delusional disorder are personal and family therapy.

Personal therapy is one-on-one counseling that focuses on building a relationship between the counselor and the patient and aims to create a positive environment where the patient feels that they can speak freely and truthfully. This is advantageous because the counselor can usually get more information out of the patient to get a better idea of how to help them if that patient feels safe and trusts them. Additionally if the patient trusts what the counsellor says disproving the delusion will be easier.

Family therapy is a technique in which the entire family comes into therapy together to work on their relationships and to find ways to eliminate the delusion within the family dynamic. For example, if someone's sister is the inducer the family will have to get involved to ensure the two stay apart and to sort out how the family dynamic will work around that. The more support a patient has the more likely they are to recover, especially since SDD usually occurs because of social isolation.

Notable cases

In May 2008, in the case of twin sisters Ursula and Sabina Eriksson, Ursula ran into the path of an oncoming articulated lorry, sustaining severe injuries. Sabina then immediately duplicated her twin's actions by stepping into the path of an oncoming car; both sisters survived the incident with severe but non-life-threatening injuries. It was later claimed that Sabina Eriksson was a 'secondary' sufferer of folie à deux, influenced by the presence or perceived presence of her twin sister, Ursula—the 'primary'. Sabina later told an officer at the police station, "We say in Sweden that an accident rarely comes alone. Usually at least one more follows—maybe two." However, upon her release from hospital, Sabina behaved erratically before stabbing a man to death.
The case of Ian Brady and Myra Hindley, Britain's notorious child killers in what became known as the Moors Murders, is another instance where folie à deux was said to occur. Hindley came, through her relationship with Brady to believe his racist philosophy that included a fascination with Hitler and fascism.
Another case involved a married couple by the name of Margaret and Michael, both aged 34 years, who were discovered to be suffering from folie à deux when they were both found to be sharing similar persecutory delusions. They believed that certain persons were entering their house, spreading dust and fluff and "wearing down their shoes." Both had, in addition, other symptoms supporting a diagnosis of emotional contagion, which could be made independently in either case.
Psychiatrist Reginald Medlicott published an article about the Parker-Hulme murder case called “Paranoia of the Exalted Type in a Setting of Folie a Deux - A Study of Two Adolescent Homicides”, arguing that the intense relationship and shared fantasy world of the two teenaged friends reinforced and exacerbated the mental illness that led to the murder: “each acted on the other as a resonator increasing the pitch of their narcissism.”
In 2016, a case involving a family of five from Melbourne, Australia made headlines when they abruptly fled their home and travelled more than 1,600 km (1,000 mi) across the state of Victoria because some of the family had become convinced someone was out to kill and rob them. No such evidence was found by the police, and the symptoms of those involved resolved on their own once the family returned to their home.
The book Bad Blood: Secrets and Lies in a Silicon Valley Startup suggests that this ailment plagued the founder of Theranos, Elizabeth Holmes, and her boyfriend/business partner Ramesh Balwani.
It was suspected a family of eleven members from Burari, India suffered from this condition. On 30 June 2018, the family committed suicide due to the shared belief of one of its members.

In popular culture

"Folie à Deux" is the title of the nineteenth episode in the fifth season of The X-Files (1998). The episode details a story of a man who believes his boss is an insect monster, a delusion that Fox Mulder begins to share after investigation.
Bug (2006) is a film that depicts a couple with a shared delusion that aphids are living under their skin.
In Season 2, Episode 3 of Criminal Minds, "The Perfect Storm" (2006), Dr. Reid mentions that the rapists had this condition.
In 2008, American rock band Fall Out Boy released their fourth album, Folie à Deux.
The independent film Apart (2011) depicts two lovers affected and diagnosed with induced delusional disorder, trying to uncover a mysterious and tragic past they share. In a 2011 interview, director Aaron Rottinghaus stated the film was based on research from actual case studies.
In 2011, in CSI: Miami (Season 9, Episode 15 "Blood Lust"), it was revealed the killer couple had this condition.
In 2012, in Criminal Minds (Season 7, Episode 19 "Heathridge Manor"), it was revealed the killer family had this condition.
In 2017, in Chance (Season 2, Episode 9 "A Madness of Two"), it was revealed the villains are suffering from this condition.
The Vanished (2020) shows a couple who lost a child continuing to hold on to the delusional thought of their existence.