Delusional misidentification syndromes DMIS8

The abilities to recognize individual faces and to discriminate between different faces are fundamental human processes and normally we are extraordinarily adept at them. The biological need for face recognition is present from birth and the capacity elaborates throughout earlier life. Changes in a familiar facial appearance can be unsettling and even frightening, not just in children but also in adults. A great deal of sophisticated neurophysiological and neuropsychological investigation has been carried out on normal and abnormal human face-recognition abilities.

A number of clearly defined neurological disorders are associated with very specific abnormalities of face recognition. (8Z) Since 1923, when Capgras and Reboul-Lachaux(6) first reported the illusion de sosies or 'delusion of doubles', there has been growing interest in abnormalities of recognition involving facial and bodily appearance and behavioural characteristics which present as psychiatric, and specifically delusional, disorders. Here we shall emphasize those cases in which a delusion of misidentification is the principal symptom of the disorder and in which the form or structure of the illness is in many ways similar to that of delusional disorder. These are the delusional misidentification syndromes. However, it is important to note that superficially similar presentations may occur as secondary features in cases of schizophrenia, severe mood disorder, or dementia, and in these we refer to a misidentification phenomenon rather than syndrome.

Clinical features(88>

There are four main variants of DMIS:

1. the Capgras syndrome, in which the patient falsely perceives that someone in his environment, usually a close relative or friend, has been replaced by an almost, but not quite exact, double;

2. the Fregoli syndrome, where the patient believes that one or more individuals have altered their appearances to resemble familiar people, usually to persecute or defraud him or her;

3. intermetamorphosis, in which the patient believes that people around have exchanged identities so that A becomes B, B becomes C, and so on;

4. the syndrome of subjective doubles, where the patient is convinced that exact doubles of him- or herself exist, a kind of Doppelganger phenomenon.

Additional alternative forms have been described and it should be noted that features of more than one variant may occur in an individual case. This is especially true of the subjective doubles phenomenon.

Although the patient is convinced of the deception, typically he is aware that something is wrong and that the replacements are subtly incorrect. Many sufferers are extremely distressed and frightened because they are convinced that the substitution of identity is meant to harm them. In some cases they become enraged and attack the 'impostor' with considerable violence. Their belief is of delusional intensity and they usually cannot be dissuaded by argument or by demonstration of contrary proof.

It is of particular interest that the misidentification is not indiscriminate but involves a limited number of usually familiar people. In some cases, substitution involves not just people but places or objects. An admixture of depersonalization and derealization is not uncommon, especially in the earlier stages.

Classification

Delusional misidentification syndromes have been regarded as something of a curiosity until recently and have not been included in DSM-IV or ICD-10. If a misidentification phenomenon occurs in the setting of another psychotic illness such as schizophrenia, then of course it is regarded as a feature of that illness. However, if it is the principal aspect of a psychosis then it should be regarded as a disorder sui generis. In those cases where there is a discrete delusional system occurring in clear consciousness and within a relatively intact personality, it would seem logical to assign the patients to a new status within the Delusional Disorder (DSM-IV) or Persistent Delusional Disorders (ICD-10) category. In other cases where organic brain disease is more prominent, the proper assignment would be to Mental Disorders due to a General Medical Condition (DSM-IV) or Organic, Including Symptomatic, Mental Disorders (ICD-10).

Diagnosis and differential diagnosis

The diagnosis is based on recognition of the patient's delusional belief, the accompanying agitation, and uncharacteristic behaviours, possibly including violent attacks on people in the environment. A full neurological investigation is mandatory.

Differential diagnosis includes the following:

• schizophrenia

• delusional disorder, persecutory subtype

• major mood disorder with delusions

• organic brain disorder

• substance abuse disorders.

Epidemiology

The frequency of DMIS is unknown. Until the past decade it was regarded as very rare, but an increasing number of cases are being reported. The disorder occurs in both sexes and across a wide age range, but particularly in middle-aged and elderly people.

Aetiology

When DMIS was first recognized, psychological, and especially psychodynamic, explanations were sought for the phenomenon. (89) The fact that the delusion usually involved the patient's nearest and dearest led to the theory that overintense affect towards significant others induced ambivalent feelings, leading to psychological splitting and projection, very much as in theories of paranoia. Such hypothesizing was based entirely on retrospective information, and it has been seriously undermined in recent years by the increasing recognition of significant brain pathology in a high proportion of cases. Also, it has been suggested that the majority of patients tend to be too old at the time of onset for a purely psychological origin to seem feasible. To date, psychodynamic formulation and therapy have not proved useful in practice.

Nowadays we have many reports on brain dysfunction in DMIS(3,9°,91) but large case series are lacking. There is some consensus that abnormalities of the right cerebral hemisphere are especially likely to be present, particularly in the right temporoparietal area, but these are not inevitable and lesions in other cerebral locations have been noted. Currently it is acknowledged that at least two-thirds of typical DMIS cases have a demonstrable brain lesion which can be regarded as causal and which may specifically bring about abnormalities of face recognition (a function mediated especially in the right hemisphere). Also, there commonly appears to be dissociation of sensory information from its appropriate affective accompaniment and failure of suppression of inappropriately repetitive behaviours (also a right-sided function). These last two phenomena are very typical of delusional illnesses in general.

We know little of the biological substrate of delusional symptoms, but one proposal is that there may be a dysfunction of the limbic-basal ganglia mechanisms involved in their genesis, with particular emphasis on dopamine overactivity. (92> In DMIS there appears to be a breakdown in integration of information between the right parietotemporal cortex, the limbic system, and certain basal ganglia, resulting in the specific misidentification quality of the delusion, associated with inappropriate emotion and inability to suppress abnormal thoughts and behaviours. In addition, there is some evidence linking disorders of the limbic lobe with 'paranoid' symptoms in general. Therefore it is possible to postulate a complex brain mechanism which normally integrates sensory and affective impulses and downregulates repetitive behaviour, and whose malfunction results in delusional beliefs, altered judgment, overintense mood, and inability to change or develop insight. The particular delusional content would be determined by the specific site within the mechanism at which the significant abnormality had its predominant affect.

Although the above is simply a paradigm, it is also a model with potential for the study of delusional and concomitant phenomena by modern neurobiological investigative methods. It also allows us to conjecture about the general similarities and specific differences between DMIS and delusional disorder, and perhaps it may help us with the classification of the former.

Course and prognosis

Although DMIS may appear insidiously, it not uncommonly comes on relatively suddenly in a previously normal individual, presumably related to the underlying cerebral pathology. Where brain damage is substantial, the prognosis is that of the brain disease. If the brain dysfunction is more subtle and does not remit, the delusional symptoms may become chronic. Forensic complications may occur if the patient becomes violent, (93> and a small number of murders have been reported in association with DMIS.

Treatment

Acute treatment may involve sedation and antipsychotic medication. Ongoing treatment is by maintenance doses of an antipsychotic with possible addition of an anticonvulsant. Psychological counselling may be beneficial as the patient recovers.

Case Study Delusional misidentification syndrome with Capgras and Fregoli features A man of 63 recovered from a relatively minor stroke with only minimal left-sided weakness. During his convalescence he became very agitated and began accusing his wife of being an impostor. He also thought that visiting relatives were being impersonated by strangers and that this was all part of a plot to deprive him of his money. He frequently threatened to strike others, although he did not actually commit violence. At times he broke down and wept copiously, apologizing to his wife somewhat over-effusively. He was admitted to a psychiatric unit where an electroencephalogram and a CT scan revealed cerebral abnormalities, especially but not exclusively on the right side. His symptoms gradually improved on anticonvulsant treatment. He returned home functioning on a somewhat limited level but apparently free of delusions.

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