In DSM-III, this disorder is called Shared Paranoid Disorder
For more information, see Paranoid Disorders
The essential feature is a persecutory delusional system that develops as a result of a close relationship with another person who already has a disorder with persecutory delusions. The delusions are at least partly shared. Usually, if the relationship with the other person is interrupted, the delusional beliefs will diminish or disappear. In the past this disorder has been termed Folie à deux, although in rare cases, more than two persons may be involved.
A. Meets the criteria for Paranoid Disorder.
B. Delusional system develops as a result of a close relationship with another person or persons who have an established disorder with persecutory delusions.
A. A delusion develops in an individual in the context of a close relationship with another person(s), who has an already-established delusion.
B. The delusion is similar in content to that of the person who already has the established delusion.
C. The disturbance is not better accounted for by another Psychotic Disorder (e.g., Schizophrenia) or a Mood Disorder With Psychotic Features and is not due to the direct physiological effects of a substance (e.g., a drug of abuse, a medication) or a general medical condition.
The diagnosis of Shared Psychotic Disorder is made only when the delusion is not due to the direct physiological effects of a substance or a general medical condition. Differential diagnosis is rarely a problem because of the history of close association with the primary case and the similarity of delusions between the two individuals is unique to Shared Psychotic Disorder. In Schizophrenia, Delusional Disorder, Schizoaffective Disorder, and Mood Disorder With Psychotic Features, there is either no close relationship with a dominant person who has a Psychotic Disorder and shares similar delusional beliefs or, if there is such a person, the psychotic symptoms usually precede the onset of any shared delusions. In rare cases, an individual may present with what appears to do Shared Psychotic Disorder, but the delusions do not disappear when the individual is separated from the primary case. In such a situation, it is probably appropriate to consider another Psychotic Disorder diagnosis.