Folie à deux
Folie à deux ('folly of two', or 'madness [shared] by 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 Jules 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 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: 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 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. 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: 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 counsellor 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.