Case Report of Shared Psychotic Disorder or ‘Folie a Deux’ in Two Geriatric Sisters

Abstract

Folie a Deux or shared psychotic disorder is a rare and poorly understood disorder characterized as transfer of delusional beliefs from one person, the primary patient, to another, the secondary patient, who are closely related. The disorder is mainly seen within a family, most often between spouses or between siblings, although it has been noted in other relationships. Females are more likely than males to both primary and secondary partner. We present a case of a 77-year-old female who was admitted for myasthenia gravis exacerbation with a two-day history of generalized weakness, multiple falls, decreased appetite and blurred vision. However, she also described a detailed and implausible story of kidnapping and extortion which, surprisingly, was validated by the patient's younger sister. Investigation of the story by police and others confirmed it to be false. A diagnosis of shared psychotic disorder was made. The delusions appeared to occur with a rapid onset and resolution. This case highlights the unusual presentation of shared psychotic disorder in two elderly women, well outside the typical age of onset for the disorder as well as its rapid onset and resolution, rather than in the setting of a chronic psychiatric illness such as delusional disorder or schizophrenia.