Discussion
The Capgras delusion can present in several different contexts. A psychiatric differential diagnosis includes disorders in the schizophrenia spectrum (brief psychotic disorder, schizophreniform disorder, and schizophrenia), schizoaffective disorder, delusional disorder, and substance-induced psychotic disorder. In addition to psychiatric disorders, the Capgras delusion has been shown to occur in several medical conditions, which include stroke, central nervous system tumors, subarachnoid hemorrhage, vitamin B12 deficiency, hepatic encephalopathy, hypothyroidism, hyperparathyroidism, epilepsy, and dementia.1,2,4,7
A 2007 retrospective study by Josephs examined 47 patients diagnosed with the Capgras delusion from several tertiary care centers. Of those patients, 38 (81%) had a neurodegenerative disease, most commonly Lewy body dementia (LBD).1 In his review of the Josephs study, Devinsky proposed that the loss of striatal D2 receptors in LBD may be implicated in the manifestation of Capgras delusions.2 The data suggest multiple brain regions may be involved, including the frontal lobes, right temporal lobe, right parietal lobe, parahippocampus, and amygdala.1,2 Most patients in the Josephs study demonstrated global atrophy on imaging studies. One hypothesis is that it is the disconnection of the frontal lobe to other brain regions that may be implicated.1,2,4 This results in intact recognition of facial features of familiar people, impaired emotional recognition, and impaired self-correction due to executive dysfunction.
Methamphetamine also has been implicated in a small number of cases of Capgras; the proposed mechanism involves dopaminergic neuronal impairment/loss.1,2 Additionally, Capgras delusions have been described in cases of patients treated with antimalarial medications, such as chloroquine.8 Younger patients with the Capgras delusion were more likely to have purely psychiatric comorbidities—such as schizophrenia, substance-induced psychosis, or schizoaffective disorder—as opposed to underlying medical conditions.1 In the case presented here, the Capgras delusion was thought to be due to a disorder in the schizophrenia spectrum, specifically schizophreniform disorder.
Because an increasing amount of evidence indicates that the Capgras delusion is associated with certain medical conditions, a workup should be performed to rule out underlying medical etiology. Of note, no official guidelines for the workup have been produced for the Capgras delusion. However, the workup may include brain imaging, such as magnetic resonance imaging and/or CT scan to rule out mass lesions, vascular malformations, stroke, or neuro-infectious processes; laboratory tests, such as vitamin B12, liver panel, HIV, rapid plasma reagin, hepatitis B and C viruses, parathyroid hormone levels, urine drug screen, and thyroid panel can be ordered to rule out other medical causes.1,2,6,7,9
Consultations with internal medicine and neurology departments may be beneficial. Although treatment of the underlying condition may lead to an improvement in the symptoms, full remission in all cases has not been consistently demonstrated in the current literature.5,7,9,10 Patients with the Capgras delusion are challenging to treat, because their delusions have been shown to be refractory to antipsychotic therapy. However, antipsychotics are currently the mainstay of treatment. Some case studies have shown efficacy with pimozide, tricyclic antidepressants, and mirtazapine.6,9
One case study in 2014 in India of a 45-year-old woman who believed her husband and son were replaced by imposters out to kill her, showed a 40% to 50% reduction of paranoia, irritability, and suspicious scanning behaviors with a combination of risperidone and trihexyphenidyl. Despite the improvements, the woman continued to have delusions.7
A notable feature associated with those experiencing the Capgras delusion is the increased risk of violent behaviors, often because of suspiciousness and paranoia. A 2004 review suggested the risk of violence and homicidality is much higher in male patients compared with that of female patients with the Capgras delusion.9 This is despite evidence suggesting that the prevalence of the Capgras delusion seems to be greater in women.6,9 Moreover, patients often demonstrated social withdrawal and self-isolation prior to violent acts. The victims often were family members or those who live with the patient, which is consistent with the evidence that those most familiar to patients are more likely to be misidentified.1,2,7,9,10
A 1989 case series that examined 8 cases of the Capgras delusion listed the following violent behaviors: shot and killed father, pointed knife at mother, held knife to mother’s throat, punched parents, threatened to stab husband with scissors, nonspecifically threatened physical harm to family, injured mother with axe, and threatened to stab son with knife and burn him. Seven of the 8 patients lived with the misidentified persons, and 5 of the 8 patients were treatment resistant. The study posited that chronicity of the delusion, content of the delusion, and accessibility of misidentified persons seemed to increase the risk of violent behaviors. These authors went on to suggest that despite the appearance of stability, patients may react violently to minute changes.10 Overall literature seems to suggest the importance of performing a violence and homicidality assessment with special attention to assessment for themes of hostility toward misidentified individuals.9,10
Conclusion
The Capgras delusion is an uncommon symptom associated with varied psychiatric, medical, iatrogenic, and neurologic conditions. Treatment of underlying medical conditions may improve or resolve the delusions. However, in this case, the patient did not seem to have any underlying medical conditions, and it was thought that he may have been experiencing a prodrome within the schizophrenia spectrum. This is consistent with the literature, which suggests that those with the delusions at younger ages may have a psychiatric etiology.
Although this patient was responsive to aripiprazole, the Capgras delusion has been known to be resistant to antipsychotic therapy. It is worth considering a medical and neurologic workup with the addition of a psychiatry referral. Further, while the patient in the presented case had the delusion that he had assaulted his mother, whom he misidentified as an imposter, the patient did not demonstrate any hostility and denied thoughts of harming her. However, given the increased risk of violence in patients with the Capgras delusion, a homicidality and violence assessment should be performed. While further recommendations are outside the scope of this article, the provider should be cognizant of local duty-to-warn and duty-to-protect laws regarding potentially homicidal patients.
