Bound by belief and entangled minds: Shared psychosis in two isolated mother-daughter dyads from a Sri Lankan psychiatric setting: A Case Series of Folie à Deux in an Acute Female Inpatient Unit

Background: Shared psychotic disorder (folie à deux), first described by Lasègue and Falret in 1877, refers to the transmission of delusional beliefs from a dominant individual to a closely associated secondary, usually in the context of social isolation (1). Although it is no longer a distinct entity in DSM-5 or ICD-11 (2,3), it remains clinically significant, particularly among dyads with emotional dependence, disability, or sensory deprivation.
Case presentation: We describe two mother-daughter dyads admitted to a female inpatient psychiatric unit in Sri Lanka. Both pairs had lived in extreme isolation and developed elaborate delusional systems reinforced by mutual dependence. The first dyad included a mother with congenital deafmutism and her daughter with cerebral palsy, epilepsy, and intellectual disability. The second comprised a mother with schizoaffective disorder and her daughter, recently separated from her spouse. In both instances, the daughters improved markedly following separation, confirming their roles as secondaries, while the mothers required more intensive interventions, including electroconvulsive therapy.
Conclusion: These cases illustrate folie communiquée within isolated family settings and highlight the importance of early recognition, separation, and culturally sensitive multidisciplinary management. They also underscore current nosological debates: although both cases fulfilled Dewhurst and Todd's classical criteria for folie à deux (4), they would now be classified within broader schizophrenia spectrum disorders in DSM-5 and ICD-11 (2,3).