There are several types of delusional misidentification syndromes (DMS), some of which are

• Capgras delusion is where the individual feels that a closely related individual has been replaced by an exact double.

• The syndrome of Fregoli is where familiar people are identified in strangers.

• The syndrome of Intermetamorphosis is where the patient believes than an individual has changed physically and psychologically into another person, the individual is often a persecutor and there may well be similarities between the individual and persecutor.

• The syndrome of Subjective Doubles is where the patient believes another person has been physically transformed into his own self.

• It can extend to objects and is associated with a feeling of ambivalence to the object / person of misidentification.

 

Those with these delusions are often schizophrenic, though it can be found in organic illness and mood disorders. As well as existing separately in delusional disorder, though this is not common (Sims 2003). DMS has been associated with violence, with the delusions of misidentification probably being accompanied by delusional beliefs that the misidentified person has not only changed but is also aiming to do harm to the patient and hence make them a legitimate victim of violence (Aziz 2005).

 

There seem to attributes that are associated with DMS in that objects or people misidentified are nearly always important to the sufferer. There is an appreciable lack of insight, high levels of conviction in these misidentifications and often accompanied by denial.

 

In terms of what may cause it, it seems that it can’t be explained by visuospatial defects. The disconnection hypotheses can’t explain the delusional and multimodality nature of DMS. Others have suggested that confabulations (erroneous statements without a conscious desire to deceive) are involved somehow. They are often associated with confused memory recollections. Simple confabulations are partly due to temporal misalignment of memories and fantastic confabulations are bizarre utterances with no connection to real memory. The frontal lobe impairment that has been found with confabulation may be associated with poor memory retrieval. Interestingly, confabulations after anterior communicating artery aneurysms tend not to be delusional. Some say that motivational processes lie behind DMS in that people may ‘take’ themselves somewhere better. The authors postulate right hemisphere damage alters aspects of self-processing, with right frontal damage resulting in the feelings of familiarity being disconnected from personally relevant information and so internal drives may become viewed as external (Feinberg 2005).

 

Some studies have implicated abnormalities in the processing of the human face in delusional misidentification (Phillips 1995). The face contains a large amount of socially relevant information, e.g., it helps us to recognise the age and gender of an individual, assess their familiarity and determining facial expression. It is so important that facial recognition has its own neural circuitry. Facial recognition is part of the process of recognising the self and is so central, that we tend to have a sense of self by 18 months. With facial self-awareness tending to develop around the months of 18 to 24 (Gillihan 2005). The right hemisphere is involved in facial recognition but, when the face is distorted (e.g., half familiar and half unfamiliar) the left hemisphere may also be involved, as part of a self-memory system

 

Damage to the brain has been clearly implicated in the origin of DMS. Two series of patients with DMS, identified as case reports in the literature, were assessed for evidence of organicity illness. Those with DMS and evidence of organic illness, tended to be older, to have more paranoid delusions and to have an abnormal CT scans. When looking at brain damage in particular, it was more likely to be in the right side (Fleminger 1993). In terms of localising pathology, a case series of 29 patients with misidentification for people were found to have damage in the frontal, temporal and parietal lobe in 88% / 73% / 60% respectively. Another case series found 52% with right brain hemisphere involvement. 7% of those with reduplication misidentification had left hemisphere involvement. A prospective study of 50 alcoholics found three out of the four with misidentification had acute right hemisphere damage. Other case series have found right occipital parietal damage (Feinberg 2005). A 71-year-old lady developed delusions of misidentification; her husband became her sister, but not when speaking on the phone; she felt her home was a replica. Her MRI showed damage to the anterior right fusiform gyrus, inferior gyrus of the right temporal lobe, atrophy of the right parahippocampal and hippocampal gyri. Her neuropsychological data showed defects in visual perception and construction, low performance IQ, visual attention / memory / motor processing and executive processes (Hudson 2000).

 

As mentioned above, we seem to have a predominance of right hemispheric brain lesions, though left sided lesion are not uncommon. Neuropsychological characteristics of schizophrenics with and without DMS were analysed in a series of patients and it was found that there was no difference, but both groups had deficits in visuospatial ability, executive function, attentional function and visual construction memory. Some feel that lesions in the brain disconnect functional areas, e.g., temporolimbic and frontal regions, separation of the hippocampus may lead to information not connecting with the correct memories, leading to duplications. Ellis and Young feel that a disconnection between the dorsal visual pathway (possibly responsible for emotional forms of facial recognition) and the ventral pathway, from the visual cortex to the temporal lobe (involved in cognitively processing information), may be needed for DMS, specifically damage to the ventral route. Problems for many theories are that there are features of DMS that can’t be easily explained, e.g. blind people can develop DMS, proximity is not required for DMS, DMS can occur in the auditory modality but not the visual one and the presence of abnormal face processing does not necessarily lead to delusions (Lykouras 2008; Feinberg 2005).

 

Another case series of seven patients, of which six were males, ranging in age from 63 to 84, with mini mental state scores from 19 to 28, found they recognised faces of familiar people / emotional expressions and had normal visual fields. One with stroke developed Capgras for home; another had crural paraparesis and hydrocephalus with Capgras for home and wife; still another had hydrocephalus with intermittent capgras for his house, showing an improvement after a ventriculoperitoneal shunt; two had Parkinson’s disease; one died after an operation for a brain tumour; and one had Alzheimer’s Disease (Amâchio 2004).

 

Of a series of 128 patients with Alzheimer’s disease (AD), 40 had symptoms of misidentification for others, on the TV (so they felt the images were real) and mirror image (inability to recognise their reflection). Those with misidentification, as compared to AD without misidentification, tended to be male, have visual hallucinations, have larger right anterior horn (i.e., right frontal atrophy) and left anterior brain quadrants. Also, those AD with misidentification of people tended to have larger right and smaller left anterior horns and large left anterior brain quadrant (FÖrstl 1991).

 

Thirty-five patients with Parkinson’s were recruited and divided into those with and without DMS. Five had DMS in the past month and all had one type of DMS, with one having temporary prosopagnosia. Those with DMS tended to have more severe visual hallucinations, have greater impairment in auditory learning, delayed recall, reduced semantic fluency and poor naming ability. Greater temporal cortex abnormalities may be involved in DMS in Parkinson’s, as these patients had more defects in verbal memory, naming and semantic verbal fluency (Pagonabarraga 2008). It has been suggested that DMS may be more common in Parkinson’s than previously thought (Roane 1998). Further investigations of psychotic symptoms were investigated in a series of patients with Dementia of Lewy Bodies. By using factor analysis, the first factor included person misidentification, place misidentification, Capgras syndrome, phantom borders and reduplication of place and person, all with factor loadings greater than 0.5. There were 32 patients with these symptoms and they tended to show lower brain perfusion in the left hippocampus, insula, frontal operculum, ventral striatum and nucleus accumbens. The second factor was made up of reduplication of person, belief that dead relatives were still alive and a belief that absent relatives were still in the house, but there was no relation to brain perfusion patterns. Those with delusions of theft and persecution showed relative hyperperfusion in the right rostral medial frontal cortex. So, in essence, misidentification was related to limbic paralimbic structures and other delusions to frontal lobe issues (Nagahama 2010).

 

DMS has been noted in a patient with koro (a culture-bound psychiatric illness); this man developed Fregoli type symptoms to his neighbourhood, neighbours and medical staff, as well as delusions of paranoia, thought-broadcasting and hallucinations in several modalities. Although the author admitted this patient could be classified as having koro and schizophrenia, they also felt that abnormality of recognition of the body may be a more appropriate way to conceptualise matters (Altabe 2005).

 

Several different types of DMS can coexist. Capgras was observed to coexist with Fregoli in a 62-year-old schizophrenic with frontotemporal volume loss and white matter lesions (Turkiewiczl 2009). A 64-year-old man presented with Capgras and intermetamorphosis, probably in the context of cerebrovascular damage to the frontal and parietal lobes. The Capgras was directed toward his wife, in that he felt that there were different versions of his wife and occasionally he would call her an imposter. It tended to be short-lived and was worse at times of anxiety, when his wife changed her appearance, or when tired. Intermetamorphosis was less frequent and involved his wife changing into his mother-in-law. He displayed ideomotor and constructional apraxia, a verbal / performance IQ of 68, he often felt unfamiliar faces were familiar and had poor retrieval of visual information (Edelstyn 2001).

 

Memory deficits have been found in DMS, e.g., in visual memory, and executive function. Confabulation (the preservation of a cognitive response when it has ceased to be relevant) may be relevant. Those with Korsakoff’s syndrome often confuse the past and present. They feel that they are back in the past and that the people that were there in the past are the people who are actually around them in the present. This disordering of temporal ordering of memories may lie behind DMS, due to damage to the prefrontal cortex. Alternatively there may be a problem with consciously retrieving information, resulting in faulty beliefs. Problems here are that confabulation can’t explain the specificity of DMS types, and that DMS and confabulation can exist at different points in a patient’s clinical career, showing that one may not need the other (Feinberg 2005).

 

The issue of whom or what is actually misidentified was a question asked in a paper by Margaritis 2005. They said that in Fregoli delusions the sufferer misidentifies the familiar person who has got themselves into the stranger. The authors made the point that it is equally valid to say that it is the stranger who is misidentified, with the familiar person being somehow perceived behind the stranger. Another way to look at this is that there are two misidentifications here, one for the stranger and the other for the familiar person. In Capgras, the misidentification occurs for the familiar person, not the unseen stranger as in Fregoli. They also bring up the case where a complete stranger is misidentified, a stranger on whom we have no prior information, in contrast to those misidentifying familiar people. This means there is a complete lack of prior autobiographical information upon which to base decisions, e.g., in Capgras people say the person does indeed look like their father, say, but they still maintain a belief in a misidentification. This then led the authors to bring up the fact that we all have some kind of uniqueness, a recognition of which must occur before any identification (Margaritis 2005).

 

Other features that are said to be common to DMS includes duplication, selectivity (exceptional person is involved), dissociation (there is an implicit knowledge of their true identity) and adaptive aspect (there is some function to the DMS). An alternative psychopathological phenomenon that involves duplication of the self, and hence capable of being confused with DMS, is the symptom of Autoscopy (Nagy 2009). Some have suggested that depersonalisation / derealisation may proceed and lead to some forms of misidentification (Christodoulou 1978).

 

An important case review of 260 cases of DMS was performed in 1980. Patients were grouped into those who misidentified others (group 1), those for whom the self was altered (group 2), and those with misidentification of place (group 3). Group 3 were statistically less likely to have paranoia, depression and schizophrenia, while being more likely to have suffered brain trauma. Group 2 had more auditory hallucinations and cerebrovascular accidents. When it came to IQ, the verbal scores tended to be higher than the performance results. All three groups had EEG abnormalities, with left sided defects being seen in groups 1 and 3, and right side abnormalities in group 2, though CT scans showed predominately right sided abnormalities (FÖrstl 1990).

 

Progress has been made recently on the possible neurobiological basis of delusional misidentification delusions; these include the left retrosplenial area and the right ventral frontal cortex / anterior insula (McKay 2017)

 

Preliminary Analysis of DMS dataset

 

I performed a literature review, using the keywords Capgras, Fregoli, Reduplication, Intermetamorphosis, Mirror Sign, Clone, Paramnesia, Misidentification and Doubles. Databases searched included medline, pubmed, uk pubmed, google scholar and highwire for case reports using the terms. The case reports were searched for data on age, gender, relationship status, ethnic group, country of origin and number of children. Also DMS symptom type, number of different DMS symptoms, presence of mental illness, presence of neurological impairment, medication, other delusion types, number of other delusion types.

 

Limitations – Data are often missing, many cases were prior to the era of neuroimaging. It is impossible to determine causality. Different criteria may have been used to determine which DMS type was present. Any results are correlative and not associative.

 

General results – This section reports the raw data, without any accounting for missing data.  There were 505 case reports found in the literature. The mean age was 47yr with a range from 9 to 94. 45% were female, 62% were unemployed, 9% were in a relationship, 89% had a medical history, 70% abused substances or alcohol. 84% had a psychiatric history, 39% had a family psychiatric history. 90% had children with the mean number of children per case was 2.1. The average duration of misidentification was 2.7yr.

 

381 had Capgras, 53 had fregola, 33 had intermetamorphosis, 71 had duplication, 18 had mirror sign, 46 had the copies type, 50 had reverse type. Patients had between 1 to 5 types of misidentifications.

 

170 hallucinated, 490 had other delusional types, 250 were treated psychiatrically with the response noted in 257.

 

414 had misidentification involving others, 444 involved humans, 154 involved their spouses, 101 cases misidentified their parents. 70 misidentified themselves, 85 misidentified their children and 73 misidentified objects