Psychosis refers to symptoms such as delusions, hallucinations, disorganized thinking and speech, and bizarre and inappropriate motor behavior (including catatonia) that indicate loss of contact with reality. (See also Introduction to Schizophrenia and Related Disorders.)
Shared psychosis (previously termed folie à deux) is now considered a subset of delusional disorder. It usually occurs in a person or group of people (usually a family) who are related to a person with a significant delusional disorder or schizophrenia. The prevalence of shared psychosis is not known, but the disorder appears to be rare. The patient with the primary disorder is usually the socially dominant member in the relationship and imposes the delusion on or convinces the patient with the secondary disorder of the unusual beliefs.
Identifying who in the relationship has the primary psychosis is important because the person with the secondary disorder typically does not maintain the delusional beliefs when separated from the person with the primary disorder.
Counseling and therapy can usually help people who have a shared psychosis. Usually, the person with the psychotic symptoms needs pharmacologic treatment.