Clinical Geriatrics

Case Presentation
Mrs. G, a 76-year-old woman with a history of depression and anxiety, was admitted to an inpatient psychiatric unit after reporting a new onset of psychotic symptoms for one month. She was being treated as an outpatient prior to admission with sertraline 100 mg daily and alprazolam 0.5 mg twice a day for approximately 10 years for depression with anxiety, and was at her normal state of mental well-being until one month prior to admission. At that time, her identical twin sister, Ms. T, moved in with the patient and her husband. Ms. T had a long history of over 40 years of psychosis and carried a diagnosis of schizophrenia. She was continuously paranoid about her neighbors and kept moving from one address to another. Shortly after her sister moved into her apartment, the patient began having the same delusions, as well as auditory hallucinations of people calling out her name.
Mrs. G was brought into the hospital by her daughter after her paranoid delusions worsened and she became agitated and anxious. The patient was awake at night and believed that four young men were trying to break into her home. She was not performing her activities of daily living and was afraid to leave the apartment, even during the day. Mrs. G covered all of the windows because she believed that people were trying to look into her apartment from nearby rooftops. She was evaluated in the emergency department by the psychiatrist on call and was admitted to the hospital’s inpatient geriatric psychiatric unit. Mrs. G received a 1-mg dose of lorazepam in the emergency department for anxiety and restlessness.

On admission to the hospital, she denied any worsening of her depression since she started having the psychotic symptoms. She was anxious and worried that one of the men whom she thought was trying to break into her home would try to come and harm her in the hospital. Mrs. G was restless and paced up and down the unit. She had no known history of psychotic symptoms. There was no evidence of confusion or delirium and no recent change in the dosage of sertraline or alprazolam.

Discussion
Shared psychotic disorder, also known as “folie à deux” or induced psychosis, is a rare delusional disorder shared by two or more people with close emotional ties.1 In this disorder, an “inducer” (the primary case) who is the “originally” ill patient transmits his/her delusional beliefs to another patient.

Shared psychotic disorder was first described by Ernest-Charles Lasègue and Jean-Pierre Falret in 1877. Shared psychotic disorder is probably rare, as the rates of incidence and prevalence are unknown. The disorder is characterized by the transfer of delusions from one person to another. According to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision, diagnostic criteria for shared psychotic disorder, the delusion in the secondary case must be similar to that of the person who already has an established delusion and cannot better be accounted for by another psychotic disorder (eg, schizophrenia) or mood disorder (eg, major depressive disorder with psychosis), a substance, or a general medical condition.2 Most commonly, the primary case or “inducer” is chronically ill and is the influential partner in the relationship over a more suggestible partner.