Shared Psychotic Disorder
A delusion develops in an individual in the context of a close relationship with another person(s), who has an already-established delusion.
The delusion is similar in content to that of the person who already has the established delusion.
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.
Criteria summarized from:
American Psychiatric Association. (1994). Diagnostic and statistical manual of mental disorders, fourth edition. Washington, DC: American Psychiatric Association.