Folie À Trois: A Case of Shared Delusions Between a Patient, Her Sister, and Another Patient in the In-Patient Psychiatric Unit

Folie à deux is a rare condition in which a single person (often with a psychiatric disorder) develops a delusion that is shared by another person. Folie à troix is when a delusion is shared by three people. This case report documents the unusual case of an individual who shared delusions with two different people simultaneously. This report inspires questions about this person, her delusions, and what made them so believable to others. It is known that the development of shared delusions most commonly occurs in relative isolation and disproportionately affects individuals with preexisting psychiatric comorbidities. Because of these risk factors, delusions in a psychiatric unit may be even more “contagious” than in the general population. To our knowledge, this case report is the first to document a newly developed delusion shared between two unrelated patients in a single psychiatric unit. While physical separation of patients is the best practice in such cases, a risk-benefit analysis is needed prior to this intervention given the social barriers that may limit such an approach. Further research is needed to diagnose, manage, and optimize treatment for shared delusions in settings such as inpatient psychiatric facilities.