Delusional misidentification syndrome

# Overview
Delusional misidentification syndrome is an umbrella term for a group of delusional disorders that occur in the context of mental or neurological illness. They all involve a belief that the identity of a person, object or place has somehow changed or has been altered. As these delusions typically only concern one particular topic they are also fall under the category called monothematic delusions.
This syndrome is usually considered to include four main variants1:
- The Capgras delusion is the belief that (usually) a close relative or spouse has been replaced by an identical-looking impostor.
- The Fregoli delusion is the belief that various people that the believer meets are actually the same person in disguise.
- Intermetamorphosis is the belief that people in the environment swap identities with each other whilst maintaining the same appearance.
- Subjective doubles, in which a person believes there is a doppelganger or double of him or herself carrying out independent actions.
However, similar delusional beliefs, often singularly or more rarely reported, are sometimes also considered to be part of the delusional misidentification syndrome. For example:
- Mirrored self-misidentification is the belief that one's reflection in a mirror is some other person.
- Reduplicative paramnesia is the belief that a familiar person, place, object or body part has been duplicated. For example, a person may believe that they are in fact not in the hospital to which they were admitted, but an identical-looking hospital in a different part of the country, despite this being obviously false2.
- Syndrome of delusional companions is the belief that objects (such as soft toys) are sentient beings3.
- Clonal pluralization of the self, where a person believes there are multiple copies of him or herself, identical both physically and psychologically4.
There is considerable evidence that disorders such as the Capgras or Fregoli syndromes are associated with disorders of face perception and recognition. However, it has been suggested that all misidentification problems may exist on a continuum of anomalies of familiarity5, from deja vu at one end to the formation of delusional beliefs at the other.

# Features of delusional misidentification syndrome
- Lack of awareness or minimization of illness, functional loss, or personal problem-Many cases of delusional misidentification or reduplication manifest with denial or anosognosia. For patients who have Fregoli-type DMS, the delusions themselves often allow patients to view their situation as being DELUSIONAL MISIDENTIFICATION better  than it actually is. Thus, patients preferentially locate themselves in pleasant, familiar surroundings such as at home or at work, when actually they are confined in  hospital or rehabilitation setting. If they acknowledge being in a hospital, they tend to believe that the hospital is close to home.
- Alterations in entities of personal significance-Misidentifications and reduplications, almost universally, involve delusions concerning entities of great personal significance such as ones body, family, current location, and job situation.
- Selectivity and consistency-Patients persistently misidentify the same particular aspects of the self and environment. This persistence makes it unlikely that most cases of DMS can be attributed to general impairment in memory or perception.
- Resistance to correction-Misidentifications are fixed, false beliefs and, therefore, represent true delusions. Even when patients are confronted repeatedly with the illogical nature of the delusion, they maintain their position. Indeed, patients may demonstrate implicit or explicit awareness of their true situation This feature distinguishes DMS from other forms of confabulation (eg, amnestic confabulation) and from unawareness in general.
- Right hemisphere dysfunction-Right frontal dysfunction predominates in focal and diffuse cases of DMS regardless of the type of delusional misidentification or reduplication.

# Treatment
the treatment of the specific form of delusion has not been studied systematically. For patients manifesting any psychotic disorder in the context of a neurologic illness, atypical antipsychotics are generally recommended because of the decreased risk of adverse neurologic effects. With patients who have progressive dementia, such as dementia with Lewy bodies, in which DMS is common, cholinesterase inhibitors have demonstrated some ability to reduce psychiatric symptoms.