Shared Psychotic Disorder (Folie à Deux)

Shared psychotic disorder, historically termed folie à deux (madness shared by two), folie à trois, or folie communiquée, is a rare condition where delusions and sometimes hallucinations from a primary individual with established psychotic illness are adopted by one or more closely related secondary individuals. The condition was removed as separate diagnosis in DSM-5 (now subsumed under delusional disorder or other specified schizophrenia spectrum disorder) but remains clinically recognized. Folie à deux affects 1.7-2.6% of psychiatric admissions.

Pathogenesis involves prolonged exposure to a primary individual with psychotic illness in conditions of social isolation, intense emotional bond, dependent relationship dynamics, and shared cultural or religious beliefs that may serve as foundation for shared delusions. Common relationships include sister-sister (most common), husband-wife, mother-child, parent-child, or close friends. The primary (inducer) typically has schizophrenia, delusional disorder, mood disorder with psychotic features, or dementia, while the secondary (recipient) often has predisposing factors such as cognitive impairment, intellectual disability, dependent personality, or shared psychiatric vulnerability.

Clinical features include identical or similar delusional content shared between individuals, with persecutory, grandiose, somatic, religious, or systematized delusions being most common. The shared psychosis develops gradually over months to years of close contact. Diagnostic criteria require evidence of primary psychotic illness in the inducer, sharing of delusions with the secondary individual, no evidence of independent psychiatric illness in the recipient before the shared psychosis emerged, and absence of substance-induced or medical causation. Treatment includes immediate separation from the primary individual (often results in significant improvement in secondary), psychotherapy for the secondary individual, antipsychotic medication if delusions persist after separation, treatment of primary individual's underlying psychiatric illness, and family therapy for relational dynamics.