Abstract

Background: Capgras’ delusion has captured psychiatrists’ imaginations, but the clinical features of the delusion have rarely been studied and presented systematically. Aims: The present study systematically reviews all case reports on Capgras’ delusion in the English language in order to better understand differences between organic and functional aetiologies. Methods: All medical and psychiatric databases were searched, as were the bibliographies of published case reports, narrative reviews, and book chapters. Results: A total of 258 cases were identified from 175 papers. Functional Capgras’ delusion was more associated with a wider variety of imposters; multiple imposters; other misidentification syndromes; auditory hallucinations; other delusions; and formal thought disorder. Organic cases were associated with age; inanimate objects; memory and visual-spatial impairments; right hemispheric dysfunction; and visual hallucinations. Executive dysfunction and aggression were associated with both types. Conclusions: Specific features of the ­Capgras’ delusional content and associated signs point to either organic or functional aetiology. The delusion is more amorphous than many theorists have supposed, which challenges their explanatory models.

© 2019 S. Karger AG, Basel

Introduction

Capgras’ delusion of misidentification has an almost totemic status in the neuroscientific understanding of psychopathology [1, 2]. The original paper [3] describing Mme M’shorrific enmeshment in a logarithmic expansion of doubles reads more like a short story by Edgar Allan Poe than a medical case history. Following the death of two daughters and twin boys, she became convinced her only remaining daughter had been abducted and replaced by an imposter, who in turn was replaced by another; so, over a 4-year period she encountered more than 2,000 doubles of her surviving daughter. Amidst this, she believed her husband had been murdered and another set in his place. The entire police force was duplicated numerous times, hence her inability to secure justice. Likewise, the doctors in the hospital multiplied, each undermining orders given by his predecessor. Explanatory models for this intriguing phenomenon seem to proliferate at a similar rate, though it was Capgras himself who set the range of options. His initial proposal was strikingly similar to contemporary [4, 5] cognitive neuropsychiatric accounts:

(S)ome faces that she sees with their normal features, the memory of which is not altered in any way, are nevertheless no longer accompanied by this feeling of exclusive familiarity which determines direct perception, immediate recognition [6].

In a subsequent paper, however, he and co-author Carrette co-opted Freudian explanatory concepts. A young woman’s delusion that her parents were imposters could then be conceived as a solution for an erotic attachment to her father [7]. Psychodynamic theorising dominated thinking about the delusion until Gluckman’s 1968 paper [8] described a case occurring in the context of proven neurological disease. Since then, a number of neuropsychiatric conditions have been associated with the onset of the delusion, somewhat undermining interpretations rooted in psychodynamic conflict.

The subsequent cognitive neuropsychiatric explanation has received considerable attention from psychiatrists, neuropsychologists, and philosophers alike; it oftentimes appears to be regarded the Rosetta stone to open the way to an explanation of all delusions. Indeed, Daniel Dennett, a renowned philosopher of neuroscience described Capgras’ delusion as an “amazing phenomenon (that) should send shock waves through philosophy” [9]. Nevertheless, all theorising about Capgras’ delusion appears to rest on strong assumptions about the narrowness of the delusional content. Enoch and Ball [10], for instance, described personal specificity, meaning that the delusion is generally restricted to the closest relative who is persistently misidentified. Any spread of the delusion is highly restricted to other intimates. This, however, looks nothing like Capgras’ original case of Mme M. who reported a logarithmic expansion of doubles implicating every stratum of Parisian society. Enoch’s review also reported 25–40% of cases occur in the context of diverse “organic disease,” and that neuropsychological abnormalities imply predominantly right and bilateral cerebral dysfunction.

Recent prevalence studies in first episode psychosis [11] have suggested it is more common than previously supposed [12], although the measures used in the first episode population lack any specific item for the Capgras’ delusion, so the reported prevalence rate of 14% must not be taken at face value. The true prevalence is thus unknown, but clinical experience would suggest that Enoch was correct to consider it rare. Nevertheless, little is known of the prognosis and response to treatment or whether there are systematic differences between Capgras’ syndrome associated with “functional” and “organic”1 disorders. Previous reviews have selected only a proportion of published cases. Fleminger and Burns [13] for instance reported on 100 published cases, half having a presumed organic aetiology and the other half with functional, while Edelstyn and Oyebode’s narrative review is comprehensive but does not explore the clinical features and associations statistically [14]. Combining numerous case reports and case series for statistical meta-analysis is an unusual but accepted methodology [15] that has proven able to enhance our understanding of rare conditions [16, 17]. This study aims to collate all cases of Capgras’ delusion published in the English language to better ­understand the clinical profile of this uncommonly important psychopathological phenomenon and to statistically explore differences between functional and organic cases.

Methods

Search and Selection Strategy for Studies

All papers published in English since Capgras’ case report was published in 1923 were sought. On 31st March 2017, we searched Medline (from 1950), PsychINFO (from 1806), Embase Classic (from 1947 to 1979), and Embase (from 1980 to January 2009). We used the key words “Capgras delusion” OR “Capgras disorder” OR “misidentification disorder(s)” OR “misidentification syndrome” AND “case report(s)” AND “meta-analysis” OR “systematic review” OR “literature review.” The titles and abstracts online were reviewed by the authors, and we obtained copies of all publications that appeared relevant to the study question. The reference lists of all these publications were then hand searched for additional relevant studies. Papers were excluded if they presented a misidentification syndrome other than Capgras’ delusion.

Data Extraction and Analysis

Two authors (N.P. and C.P.) independently extracted all the relevant data from the papers, and where they disagreed a third reviewer (N.A.) was consulted. The following information was collected systematically and entered into a Microsoft Excel database: title, journal, year of publication, age, gender, marital status, co-morbidities (medical and psychiatric), alcohol, substances, family psychiatric history, relationship with imposter, animate/inanimate double, duration of delusion, comorbid psychiatric symptoms, co-occurring misidentification delusions, neuropsychological investigations and results, neuro-imaging results (type and location of lesion), EEG. Not all parameters were available in every case reported; unreported parameters were not included in the analyses.

In addition to describing the clinical features of Capgras’ delusion with the use of frequency statistics, we analysed whether these differed between cases with an organic and those with an underlying functional diagnosis (see Box 1 for paradigmatic cases of functional and organic Capgras’ delusion). All the variables were then associated with organic versus functional by cross-tabulation (Pearson’s χ2). Fischer’s exact test was used when one or more cells in the 2 × 2 table contained 5 cases or fewer. Odds ratios and 95% CIs were calculated on Microsoft Excel for Windows and a p value less than 0.05 was considered significant.

Results

We identified 218 papers, 175 of which were found to meet the study inclusion criteria (see Appendix 1 for references). The papers reported 258 cases presenting with Capgras’ delusion. Of these, 144 described the delusion occurring in the context of functional psychiatric disorder, with 111 having an identified organic aetiology. The breakdown of primary psychiatric disorders is shown in Table 1. The most frequent diagnoses were schizophrenia (n = 83; 32%), followed by organic psychosis (n = 50; 19%) and dementia (n = 39; 15%). This was predominantly unspecified dementia (n = 15) followed by Lewy body/Parkinson’s disease dementia (n = 15; 6%). Two cases were reported as a combination of functional and organic aetiology, while one case report did not discuss underlying diagnosis at all. These three were therefore removed from the statistical analyses in Table 2; hence, the total number of cases analysed was 255.

Table 1.

Table 2.

The first case reported in the English language was published in 1963, and the most recent in 2016. The male to female ratio was 1:1.4. The median age of all cases was 45 ranging from 8 to 94 years old. The median age of cases reported to have a “functional” diagnosis was 37 (SD 15.87), while it was 64 (SD 19.68) in the “organic” group. This difference was highly significant statistically (p < 0.01). Before 1990, the percentage of functional diagnoses constituted 64% of the total reported, while after that year they comprised 53% of all the cases representing a trend but not a statistically significant reduction (χ2 = 3.1908; p = 0.08). In terms of quality of the case reports, 21% of them included 75% or more of the parameters of interest; another 58% described between 50 and 74% of the parameters; while the remainder described 49% or fewer. Nearly 80% of the case reports can be considered of moderate quality or above.

The clinical features of Capgras’ delusion are presented in Table 2. There was no difference in gender between organic and functional groups. There were, however, numerous differences between organic and functional cases with regard the person’s relationship to the imposter. Misidentifications concerning the spouse and inanimate objects were statistically significant for the organic causes of the delusion, whereas misidentifying a parent or stranger, the syndrome of subjective double, and multiple imposters were all significantly associated with functional disorders. Symptoms associated with Capgras’ delusion also differed between organic and functional cases. Additional delusions, auditory hallucinations, homicide, aggression, and other misidentification syndromes were significantly more frequent when the delusion occurred in the context of a functional psychiatric disorder. Formal thought disorder was also significantly more associated with functional than organic disorders. Visual hallucinations were statistically more frequent in organic causes of the delusion. The duration of the Capgras delusion in functional disorders ranged from 3 days to over 10 years, while in organic conditions, it was reported from 1 week to over 10 years.

Table 2 shows that 65% of all cases were considered to have responded well to treatment, with no discernible difference in response rates between groups. Antipsychotic medications were reported to be prescribed in 165 of cases, including clozapine (10). Of these, some were co-prescribed an antidepressant medication (27), benzodiazepines (10), lithium (9), anti-dementia medication (8), and anti-epileptic mood stabilisers (16). The use of other physical treatments was relatively rare: ECT (17), insulin coma therapy (4), leucotomy (1), cingulotomy (2), intravenous immunoglobulin therapy (1), and deep brain stimulation (1).

Table 3 presents differences between functional and organic groups in terms of neuroimaging, EEG, and neuropsychological testing. As one would anticipate, memory and visuospatial were more commonly impaired in organic cases, as were EEG and neuroimaging abnormalities. Of the 258 cases identified, 161 (62%) underwent some form of neuroimaging. CT was the most frequent method (109; 68%) followed by MRI (47; 29%), and then SPECT (14; 9%). Those reported as organic Capgras’ delusion were significantly more likely to demonstrate some abnormality on neuroimaging. 67% of such cases did so against 27% of those with functional Capgras. Of those with identifiable abnormalities, global atrophy was found in 57 (35%) and a fronto-temporal pattern of atrophy in 29 (12%). Typically, however, only laterality of the atrophy or lesion was reported giving a ratio left:bilateral:right of lateralisation of 7:14:14. Therefore, 80% of the cases that had identifiable cerebral pathology demonstrated an abnormality involving the right hemisphere. Likewise, 37 (35%) of the 107 cases who had an EEG were found to have some form of abnormality, predominantly in the right hemisphere (L:R; 2:7).

Table 3.

Discussion

This study collates all cases of Capgras’ delusion reported in the English language medical literature since the first case report was published in 1963. When cases were first published in English, Capgras’ delusion was believed to occur mainly in schizophreniform psychoses [18], and explanations for the peculiar content were sought exclusively in terms of interpersonal dynamics. The intimacy of the relationship and conceptual frameworks of the time precluded alternative forms of explanation. Since Ellis and Young’s seminal paper in 1990 [4], which revived Capgras’ original explanation that the delusion occurs due to the loss of affective familiarity for faces in the presence of intact facial recognition, the proportion of cases describing the delusion in the context of neurological disorder has increased, as has the utilisation of physical and neuropsychological investigations. Thus, cognitive neuropsychiatric accounts for the delusion and its particular content are ascendant.

While 258 case reports over a 52-year-period averages just 5 cases annually, there was a very definite increase in reporting of cases in the late 1980s that peaked in the years 1990–1994. Comparing this study to a thorough review of the misidentification syndromes conducted over 25 years ago [19], we found a smaller proportion of cases were attributed to functional psychiatric disorders and corresponding higher rate of organic aetiologies. In that paper, 73% of the Capgras’ delusion cases had an underlying diagnosis of schizophrenia, and 26% were associated with neurological disorders, against 32 and 43%, respectively, for ours. Nevertheless, schizophrenia remains the largest single disorder associated with case reports of Capgras’ delusion and organic delusional disorder, with its multifarious medical aetiologies, a distant second at 19%.

Unsurprisingly, the mean age of cases in functional and organic presentations differs. Nevertheless, given schizophreniform illnesses tend to present in the late teens and early twenties the mean age (36 years) of cases with a functional Capgras’ delusion is old, but probably reflects the long mean duration of the delusion in the functional group. Those with neurological disorder associated with onset of the delusion had a mean age of 64 and large standard deviation, in keeping with their presentation in middle to late adulthood, especially as Capgras’ delusion in dementia tends to occur in the later stages [18].

The identity of the imposter is significantly associated with the reported underlying aetiology. Those whose Capgras’ delusion is reportedly due to functional psychiatric disorder are more likely to view their parent as an imposter, whereas the spouse is implicated in those with suspected neurological aetiology. This is likely a function of the different mean age for the groups, as older cases will be closest to a long-term partner having already achieved independence from their parents. If so, this supports the role of intimacy in the Capgras’ delusion in keeping with both the psychodynamic and neurocognitive interpretations. Against this, however, is the frequency with which strangers and multiple imposters are implicated in all cases of Capgras’ delusion – at 10 and 39%, respectively – and the not infrequent involvement of inanimate objects (17%). Indeed, it is difficult to support either type of theory when around a quarter of cases present with such incompatible content. Multiple imposters are significantly more likely to occur in functional cases, while the involvement of inanimate objects would seem to suggest organic aetiology.

De-realisation/depersonalisation has been described as an occasional component in the genesis of the delusional belief [20] and, accordingly, it was described only rarely in these cases. Its scarcity might be thought to undermine Christodoulou’s theory [21] that Capgras’ delusion is a consequence of extreme depersonalisation but that author suggested the delusion developed as a means of ameliorating distressing strangeness and unreality. The question of why depersonalisation is resolved this way in some but not others is left unanswered.

As has been described previously [18, 22], aggression and even homicide are frequently associated with Capgras’ delusion. Homicide was reported in 6% of the functional cases, which might indicate the delusion is even riskier than previously thought or, more likely, represents publication bias. While infrequent, homicide was statistically associated with functional disorder (p = 0.045). Although aggression was significantly associated with functional (38%) rather than organic aetiology, it was nevertheless a relatively frequent finding in the latter (23%). This moderate association with violence is clinically important but, from another perspective, raises puzzling philosophical questions. Why do the non-violent Capgras sufferers, who constitute the majority, seem to live peaceably with their imposter? The frequent failure to act on the delusional content has motivated some to question the rationality of those suffering with Capgras’ syndrome [23] and even whether delusions are beliefs at all [24]. Such considerations are outside the scope of this review, but the answers bear on the coherence of competing theoretical models. A one-stage model of delusion formation, such as Maher’s [25], implies that rationality is preserved and the delusional belief should be reasonably well integrated. Two-stage models, on the other hand, posit an additional factor such as paranoid and suspicious mood [11] or impaired monitoring and evaluation of newly formed beliefs [2], which diminishes their status as such. The two-stage model is more compatible with the inaction and acquiescence noted in these case reports.

Other misidentification syndromes co-occurred in nearly 1 in 7 of the functional cases (13%) but were rare in the organic ones (3%), a statistically significant difference. The greater reporting of visual hallucinations in the organic group (19 vs. 8%) is unsurprising given they are considered almost pathognomonic of cerebral dysfunction [26] but could also suggest that perceptual abnormality plays a role in those cases. Conversely, auditory hallucinations were significantly more common in functional (35%) than organic cases (12%). Given many organic causes of the delusion would be neurodegenerative in nature, it is somewhat surprising that treatment was equally effective in both groups, with two-thirds of all case reports describing a favourable outcome.

As is to be expected, neuropsychological, neuroimaging, and EEG abnormalities were significantly more common in the organic group. However, neuropsychological abnormalities in all domains were commoner than might have been supposed in the functional group, while visuospatial and memory impairments were especially associated with organic aetiology. This finding superficially accords with a literature emphasising memory impairment in misidentification syndromes [27]. It is an occipito-hippocampal disconnect between stored memories and new experiences that is, however, suggested as the cause of the misidentification rather than impaired memory per se. Executive dysfunction occurred in 63 and 78% of functional and organic cases, respectively, a difference that was not statistically significant. This very high rate of executive impairment in both groups is in keeping with two-stage models of delusion formation which blame faulty reasoning for the apparent bizarreness, irrationality, and incorrigibility of delusional content [28, 29].Where cerebral dysfunction has been demonstrated, it overwhelmingly implicates the right hemisphere, compatible with Cutting’s hypothesis that judging familiarity is a non-dominant function [30]. Yet the failure to recognise people and objects associated with widespread dysfunction in one hemisphere is difficult to reconcile with the narrow focus of Capgras’ delusion or its frequently bizarre content. This result also differs from the study by Bell et al. [31], which identified 84 cases of Capgras’ delusion. Of these, 40 underwent some form of neuroimaging, but abnormalities were detected in only 14. A right-sided abnormality was the least common finding in their series, with diffuse bilateral pathology the commonest (9/14). A more recent similar study identified a further 34 patients with Capgras’ delusion from the electronic records of a London Mental Health Trust. Only 7 of these had neuroimaging reported, and none showed a right lateralised neuropathology. It may be that these populations, drawn from two inner-London healthcare providers, may not represent the Capgras’ delusion patients who are deemed worthy of publication as case reports in neurology and psychiatry journals. Specifically, given the mental health setting, the two studies may be largely identifying cases that would be regarded as functional in this paper. Nevertheless, these discrepancies are significant and worthy of further investigation [32].

It was at one time suggested that Capgras’ delusion arose as a consequence of impaired facial recognition, similar to prosopagnosia. However, this was soon discounted as the conditions bore little similarity upon closer analysis [10]. In fact, a double dissociation has been found between prosopagnosia and Capgras’ delusion. Prosopagnostics have a preserved skin conductance response (SCR), a proxy for emotional arousal, but impaired explicit identification of familiar faces. Cases of Capgras’ delusion demonstrate the obverse, with loss of affective familiarity with intact identification. It is this mismatch between emotional and intellectual recognition that is said to give rise to the delusional belief in imposters. The abnormal SCR was demonstrated in a case recently described by Bobes et al. [33] alongside diffusion tensor imaging abnormalities in the inferior fronto-occipital fasciculus (IFOF) and intact inferior longitudinal fasciculus. These pathways are believed to subserve respectively emotional and explicit facial recognition. Interestingly, the IFOF abnormality was confined to the left hemisphere, which contradicts our finding that neuroimaging predominantly implicates right hemispheric pathology.

Because many, albeit fewer, of the functional patients demonstrated neuroimaging and neuropsychological abnormalities, the results seem to support the proposal by White et al. [34] and others [35] to end the distinction between neurological and psychiatric disorder implicit in the functional/organic dichotomy employed here. However, acknowledging the involvement of the brain in mental disorders does not necessitate a merger of the fields [36]. A recent meta-analysis of neuroimaging findings in psychiatric and neurological conditions found that there are differences in the regions and networks involved [37]. There was greater involvement of the basal ganglia, insula, lateral and medial temporal cortex, and sensorimotor in neurological disorders with the medial frontal cortex, anterior and posterior cingulate, superior frontal gyrus, and occipital cortex disproportionately affected in mental disorders. The differences between the functional and organic Capgras’ delusion can therefore be a helpful clinical pointer towards the correct underlying aetiology.

This study is limited by the variable quality of case reports and publication bias. Only 21% of case reports were graded as high quality, so important clinical information including results of investigations was missing in 79% of the cases analysed, which introduces a bias that limits the interpretability of the findings. This probably affected disproportionately those considered functional cases, as they are likely to have been less extensively investigated, so abnormalities may have gone undetected. Some cases could be spuriously labelled organic due to a concurrent but causally irrelevant medical diagnosis, while truly organic cases might have wrongly received a functional diagnosis, particularly in those reports predating the widespread use of neuroimaging and other investigations. There is little standardisation to guide the writing of case reports, so the quality of description therein depends on the most salient features of the case and idiosyncrasies of the authors. It would be helpful if future case reports gathered detailed information on the phenomenology of the delusion, the subject’s personal and medical background, plus investigations including neuroimaging, EEG, and neuropsychological testing. The steadily rising proportion of organic Capgras’ delusion is unlikely to reflect ­increased prevalence, instead demonstrating that case ­reports follow fashions in theory; an instance of confirmation bias strengthening belief in the cognitive neuropsychiatric account of the delusion that stimulates additional case reports in a similar vein. The findings in this review must therefore be interpreted with great caution. The features of a case that make it suitable for publication probably means it is not representative of Capgras’ delusion cases generally. Our frequency statistics should not be taken as epidemiological.

Conclusions

Capgras’ delusion is a fascinating psychopathological phenomenon that presents in a wide range of psychiatric and neurological disorders with subtly differing patterns dependent on the underlying aetiology. The difference between organic and functional cases is at the level of delusional content, associated psychopathology, neuropsychological findings, and biomedical investigations. An underlying neurological disease should be suspected where the delusion concerns a spouse or inanimate objects and is associated with visual hallucinations, while a functional disorder is suggested by multiple imposters, strangers, subjective double, additional delusions, and auditory hallucinations. Fortunately, most sufferers can expect a good response to antipsychotic medication, irrespective of aetiology, but the clinician should always be mindful of the risk of aggression and homicide.

It is worth noting that the circumscribed delusion about which theorists speculate bears limited comparison to the clinical phenomena reported here and elsewhere [31]; the delusion appears more amorphous than theorists have supposed. If Capgras’ delusion is to become the Rosetta stone for delusion generally, then their theories need to account for the delusion as it is actually encountered, lest they be accused of jumping to conclusions and other reasoning errors.

Disclosure Statement

None of the authors have anything to declare.

Author Contributions

C.P. and N.P. were involved in originating and developing the research question. C.P., N.P., and N.A. were involved in data gathering and analysis. C.P. and N.P. were involved in writing the first draft of the paper with comments and feedback from N.A. for subsequent drafts.

Appendix

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Dr. Norman Poole Consultant Neuropsychiatrist, Neuropsychiatry Service 2nd Floor Grosvenor Wing, St. George’s Hospital Tooting, London SW17 0QT (UK) E-Mail norman.poole@gmail.com

Article / Publication Details

Received: October 29, 2018

Accepted: April 15, 2019

Published online: July 19, 2019

Issue release date: September 2019 Number of Print Pages: 13

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Number of Tables: 3 ISSN: 0254-4962 (Print)

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