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 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
Either the situation where two people considered to independently experience psychosis influence the content of each others 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 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 persons 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 stressed, an individuals adrenal gland releases the "stress hormone" cortisol into the body, increasing the brains 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. Taking into consideration the individuals circumstance which entails 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 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 patient 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.