Delusional misidentification syndrome

Delusional misidentification syndrome is an umbrella term, introduced by Christodoulou (book "The Delusional Misidentification Syndromes", Karger, Basel,1986) for a group of delusion

Delusion

A delusion is a false belief held with absolute conviction despite superior evidence. Unlike hallucinations, delusions are always pathological...

al disorders that occur in the context of mental

Mental illness

A mental disorder or mental illness is a psychological or behavioral pattern generally associated with subjective distress or disability that occurs in an individual, and which is not a part of normal development or culture. Such a disorder may consist of a combination of affective, behavioural,...

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 also fall under the category called monothematic delusion

Monothematic delusion

A monothematic delusion is a delusional state that only concerns one particular topic. This is contrasted by what is sometimes called multi-thematic or polythematic delusions where the person has a range of delusions...

s.

This syndrome is usually considered to include four main variants:

The Capgras delusion
Capgras delusion
The Capgras delusion theory is a disorder in which a person holds a delusion that a friend, spouse, parent, or other close family member has been replaced by an identical-looking impostor...

is the belief that (usually) a close relative or spouse has been replaced by an identical-looking impostor
Impostor
An impostor or imposter is a person who pretends to be somebody else, often to try to gain financial or social advantages through social engineering, but just as often for purposes of espionage or law enforcement....

.
The Fregoli delusion
Fregoli delusion
The Fregoli delusion or the delusion of doubles is a rare disorder in which a person holds a delusional belief that different people are in fact a single person who changes appearance or is in disguise...

is the belief that various people the believer meets are actually the same person in disguise.
Intermetamorphosis
Intermetamorphosis
Intermetamorphosis is a delusional misidentification syndrome, related to agnosia. The main symptoms consist patients believing that they can see others change into some one else both external appearance and internal personality...

is the belief that people in the environment swap identities with each other whilst maintaining the same appearance.
Subjective doubles
Syndrome of subjective doubles
The syndrome of subjective doubles is a rare delusional misidentification syndrome in which a person experiences the delusion that he or she has a double or Doppelgänger with the same appearance, but usually with different character traits and leading a life of its own. Sometimes the patient has...

, described by Christodoulou in 1978 (American Journal of Psychiatry 135, 249, 1978), is the belief that there is a doppelgänger
Doppelgänger
In fiction and folklore, a doppelgänger is a paranormal double of a living person, typically representing evil or misfortune...

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
Mirrored self-misidentification
Mirrored-self misidentification is the delusional belief that one's reflection in a mirror is some other person . Often people who suffer from this delusion are not delusional about anything else. It is considered a monothematic delusion; it is sometimes labeled a delusional misidentification...

is the belief that one's reflection in a mirror is some other person.
Reduplicative paramnesia
Reduplicative paramnesia
Reduplicative paramnesia is the delusional belief that a place or location has been duplicated, existing in two or more places simultaneously, or that it has been 'relocated' to another site...

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 false.
Syndrome of delusional companions is the belief that objects (such as soft toys) are sentient beings.
Clonal pluralization of the self, where a person believes there are multiple copies of him or herself, identical both physically and psychologically.

There is considerable evidence that disorders such as the Capgras

Capgras delusion

The Capgras delusion theory is a disorder in which a person holds a delusion that a friend, spouse, parent, or other close family member has been replaced by an identical-looking impostor...

or Fregoli

Fregoli delusion

The Fregoli delusion or the delusion of doubles is a rare disorder in which a person holds a delusional belief that different people are in fact a single person who changes appearance or is in disguise...

syndromes are associated with disorders of face perception

Face perception

Face perception is the process by which the brain and mind understand and interpret the face, particularly the human face.The human face's proportions and expressions are important to identify origin, emotional tendencies, health qualities, and some social information. From birth, faces are...

and recognition. However, it has been suggested that all misidentification problems may exist on a continuum of anomalies of familiarity, from déjà vu

Déjà vu

Déjà vu is the experience of feeling sure that one has already witnessed or experienced a current situation, even though the exact circumstances of the prior encounter are uncertain and were perhaps imagined...

at one end to the formation of delusional beliefs at the other.

See also