Importance of Capgras syndrome in shared psychotic disorder: a case report

Abstract

Shared psychotic disorder characterized by Capgras syndrome is an extremely rare condition. To our knowledge, there are only a few published papers on this condition. This paper presents a case of shared Capgras syndrome in two sisters. The inducer was a younger sister with schizophrenia, who passed on her Capgras delusion to her older sister after the death of their father. After committing a violent offense caused by Capgras delusion, a court ordered the sisters’ involuntary admission to a psychiatric hospital. After being separated and receiving antipsychotic treatment, the sisters showed substantial improvement. However, shortly after hospital discharge, they stopped taking their medication and disappeared. After 15 years, their mother died and shortly afterwards, the sisters were re-admitted for forensic psychiatric evaluation after another violent crime caused by Capgras delusion. Timely recognition, adequate treatment and maintaining a therapeutic alliance could contribute to a better clinical course and outcome of this disorder, and reduce the risk of violent behavior.

Introduction

Shared psychotic disorder is a rare mental disorder first described by the French psychiatrists Lasegue and Falret in the 19^th century, who named the syndrome “folie à deux”. Shared psychotic disorder is characterized by the transference of delusions from one person to another. The classic presentation involves an inducer with psychotic disorder who influences an induced person with a specific delusion or set of delusions. The core characteristic of this syndrome is the existence of the same delusions among multiple people. Over the last few decades, additional terms have been used to describe these phenomena, including “induced psychosis”, “imposed psychosis”, “double insanity” and “psychosis of association”. ¹

Shared psychotic disorder was first listed in the Diagnostic and Statistical Manual of Mental Disorders, Third Edition, as shared paranoid disorder. In the next edition (DSM-IV), the term changed to shared psychotic disorder. ² In the latest edition, DSM-V, it was removed as a separate entity and listed under the “Other specified schizophrenia spectrum and other psychotic disorders” category as “delusional symptoms in the partner of an individual with delusional disorder”. The DSM-V states that “in the context of a relationship, the delusional material from the dominant partner provides content for delusional belief by the individual who may not otherwise entirely meet criteria for delusional disorder”. ³

Some common themes and risk factors in the study of shared psychotic disorder include a prolonged close relationship between the inducer of the delusion and the induced, social isolation of both persons and maintenance of function without intellectual or affective disorganization in those with the disorder. The risk factors for induced persons include a passive personality, cognitive impairment, stressful negative life events, younger age than inducers and female gender.^1,4

The incidence of shared psychotic disorder is difficult to estimate, but some studies report that it is responsible for approximately 2% of psychiatric hospitalizations. ² However, this figure may be underestimated as the disorder is often missed in clinical practice because psychiatrists may treat the inducer or induced while being unaware of the existence of the delusion in the other patient(s). ¹

Earlier expert opinion that the delusions disappear in the induced person after separation from the inducer proved to be incorrect. ² Therefore, in addition to separation, the use of antipsychotic therapy is necessary for both patients. ²

It is very difficult to determine the prognosis and outcome of shared psychotic disorder, as they depend on multiple risk factors, including adherence by both patients to treatment management plans, the nature and duration of exposure to the delusion and possible premorbid personality features in affected individuals. ²

Another rare psychiatric condition is delusional misidentification syndrome. Individuals with this syndrome misidentify familiar persons, believing that they have been replaced or transformed. The syndrome occurs in a variety of psychiatric and organic disorders but appears to be strongly associated with schizophrenia.^5,6

The most common type of delusional misidentification syndrome is Capgras syndrome, which is manifested by delusional denial of identification of familial people and the belief that they have been replaced by strangers who are physically but not psychologically identical to the misidentified person. Patients with this syndrome believe that an identical stranger has replaced someone significant to them.^7–9

This syndrome is frequently related to aggression manifested toward “impostors”, and because patients have a propensity for violence, speedy recognition and timely intervention are important.^10,11 One systematic review reported that 6% of patients with Capgras delusions show violence, which may indicate that the syndrome is associated with greater risks than first assumed. ¹²

Psychotic disorders, including shared psychotic disorder and Capgras syndrome, are challenging owing to poor patient insight. Treatment includes antipsychotic medications, establishing a therapeutic alliance while negotiating mutually acceptable symptomatic treatment goals and expressing empathy and interest in the patient’s problems.^11–13

Taking into account the rarity of both shared psychotic disorder and Capgras syndrome, which were both observed in our patients, we consider this report to be of exceptional clinical and scientific value.

Case description

This case report was written according to the CARE guidelines and all patient details have been de-identified. ¹⁴ Information about the case was obtained from social worker reports, and from the patients and their mother. All case information is archived in the medical records in our hospital. Patient L is a woman in her mid-twenties; her sister, patient S, is 5 years younger than her. Both sisters were admitted involuntarily to our psychiatric clinic in 2007 because of their aggressive behavior toward their mother.

Both sisters had lived together in the same apartment since their birth; the family structure comprised themselves, their mother and their father. The family had a good social and professional standing in the neighborhood. The patients’ personal history showed that both had good psychomotor development, had graduated from university and had no reported alcohol or substance abuse. Neither sister obtained a job after college and neither had any emotional partners. In discussions about the relationship between the two sisters, the mother stated that patient S, although younger, had always been more dominant in her physical, mental and social skills. Neither patient had undergone previous psychiatric treatment.

In the case of the younger sister, social isolation, disorganized behavior, neglect of personal hygiene and the gradual emergence of incoherent speech occurred over the course of approximately 3 years. Her parents noticed that she had difficulty sleeping, talked to herself at night and occasionally expressed doubts about her origin and belonging to the family. She refused to go to the doctor, and her family did not attach any particular importance to her condition, ascribing it to a lack of friends and a job. The older sister, in contrast, did not show any symptoms of major mental disorder, but she also gradually cut off social contacts and spent time exclusively with her sister.

It seems that the death of their father was a trigger for the occurrence of major psychiatric symptoms in both sisters. They started to isolate themselves from their friends and neighbors and slowly cut all their social ties. This social withdrawal led to progressive psychological impairment resulting in shared Capgras delusion; specifically, they believed that their parents had died many years ago and that impostors had taken their place. According to reports from the mother, the induced sister began to express the Capgras belief approximately 6 months after her inducer sister had started to express the belief. Since then, the sisters had lived in complete seclusion, spending most of their time at home without any contact with the outside world. Gradually, behavioral changes such as hostility directed toward their mother and the neighborhood developed. One day, they attacked their mother with a desire to expose the conspiracy according to which their original mother was replaced by a younger person. Both sisters were brought to the emergency department by the police after this incident.

After hospital admission, at their mental state examination, neither sister showed any insight into their condition. Psychiatric assessment disclosed that the younger sister had disorganized thinking and believed that her thoughts were being placed in her mind by neighbors. She believed that her mother had been replaced by a clone and that her real mother had been killed by her neighbors, whose voices she used to hear. She justified her belief by referring to a slight difference between the “clone’s” and her real mother’s nose. In addition, she presented with delusions that her neighbors wanted to take their property, that they were damaging the furniture, that they had run cables to the house and were releasing acid through the pipes.

In contrast, the only psychotic symptom demonstrated by the older sister was the Capgras delusion that both her parents had been replaced by impostors; she ignored her sister’s other psychotic symptoms.

The diagnostic hypothesis was paranoid schizophrenia with delusional misidentification syndrome; more specifically, Capgras syndrome for the younger sister, and delusional disorder with Capgras syndrome for the older sister.

The sisters were hospitalized in two different wards, in an effort to loosen their delusional link, and had no contact with each other during their hospital stay. They both consented to treatment with antipsychotics but refused psychotherapy during hospitalization. The older sister’s treatment was successful. Within 2 months, she no longer showed Capgras delusion. In the younger sister, a slow but progressive improvement was observed, with a resolution of the persecutory ideas and voices, although her delusional misidentification did not completely disappear. After discharge, both sisters returned to their home and continued their life together. The younger sister never returned for check-ups, whereas the older sister continued to attend check-ups for approximately 3 months. During her outpatient treatment, the older sister began psychotherapy but attended only two cognitive-behavioral sessions before she stopped coming for check-ups.

There were no public records of any of the women for the period 2007 to 2023. They had seemingly disappeared. We subsequently received information that, with their mother, the sisters had moved out of the city and lived in the countryside for 15 years, until their mother died about a year ago. Subsequently, they returned to live in the city. They spent most of the time in their apartment with no social contact, but were occasionally hostile toward their neighbors. One day, the sisters physically attacked a neighbor, accusing him of replacing their parents with imposters. The police were called, and the sisters were charged with a criminal offense and brought to the same psychiatric clinic. A local court ordered an evaluation of their mental competence, their mental state at the time of the offense and the risk of reoffending.

During the psychiatric examination, the older sister, who we consider to be an induced patient, seemed to have a well-maintained and tidy appearance. She presented only with delusional misidentification syndrome, believing that neighbors had replaced her real deceased father and mother with copies of her parents.

The younger sister, who we consider to be the inducer, had a neglected appearance, flattened affect, disorganized speech and behavior and believed that she was controlled by her neighbors. She had no insight into her disorder.

Both sisters were assessed as being mentally incompetent and potentially dangerous because of their Capgras delusion. They were transferred to another forensic psychiatric hospital until the final court verdict.

Discussion

Capgras syndrome is a rare condition, but some authors maintain that it has been described in more than 10% of first episode psychosis cases.^15,16 In contrast, the incidence of shared psychotic disorder is difficult to estimate, but some studies report that it is responsible for approximately 2% of psychiatric hospitalizations. ¹

What makes this case remarkable is the longitudinal monitoring of patients with Capgras syndrome as the main symptom of shared psychotic disorder, and the presence of an induced person with no previous organic cerebral dysfunction, substance abuse or psychotic disorder.

To our knowledge, the literature contains only a few cases of induced psychotic disorder with Capgras delusions. However, in two of these cases the delusions were induced by substances, in one case the induced person had cerebral organic dysfunction, and two other cases comprised cross-sectional studies with no data on the longitudinal course of the disorder.^17–21

This case features two sisters with shared Capgras delusion. Based on their presentation (and confirmed through a subsequent clinical encounter), it seems that the sisters began to share Capgras delusions after their father died, although the younger sister presented symptoms of schizophrenia much earlier. The reason for their first involuntary psychiatric hospitalization was the violent behavior directed toward their mother and caused by Capgras delusion. After a relatively successful treatment with antipsychotics, a lack of insight led to the patients’ failure to attend check-ups and take their medication, and they moved to the countryside and lived in social isolation with their mother for 15 years. The treatment of shared psychotic disorder is challenging because patients reinforce their delusions and are therefore less likely to seek or be referred to care, which should include a combination of individual psychotherapy and pharmacological management. ²²

Soon after their mother had died, their Capgras delusion led to the sisters committing another violent crime, this time against their neighbor, who they accused of replacing their parents with imposters.

It is important to mention that both sisters met almost all of the risk factors for the development of shared psychotic disorder: delusions present in the inducer, a prolonged close relationship with each other, female gender and stressful negative life events (death of parents).^1,4 In addition, this case featured a socially withdrawn family with weak social support and rigid boundaries that contributed to a restricted social environment; this characteristic is an important factor in the emergence of shared psychotic disorder.

A chronic disease course caused by lack of insight into their disorder, social isolation and lack of compliance led the patients to commit violent offenses and to their involuntary psychiatric treatment.

Conclusion

Capgras syndrome is a rare clinical condition that can have forensic consequences and that always poses several treatment challenges. This case study highlights the need to provide competent social and medical support to families (particularly those with more social isolation and weak social support networks) of individuals with shared psychotic disorder, to prevent and mitigate risks. Greater awareness could help to prevent acts of violence in delusional patients and contribute to improvements in their care. In addition, there is clearly a need for case studies of such rare syndromes that can inform the creation of treatment guidelines. The extreme rarity of such conditions means that controlled double-blind studies are infeasible. Timely recognition, adequate treatment and maintaining a therapeutic alliance with patients could contribute to a better clinical course and outcome of the disorder, and reduce the risk of violent behavior.