Delusional Misidentification Syndromes

Delusional Misidentification Syndromes are considered some sort of an umbrella term, introduced by Christodoulou in his book 'The Delusional Misidentification Syndromes', for a group of delusional disorders that occur in the context of mental or neurological illnesses. 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 delusions.

This syndrome is usually considered to include several variants:
[1] Capgras delusion is the belief that (usually) a close relative or spouse has been replaced by an identical-looking impostor;
[2] Fregoli delusion is the belief that various people the believer meets are actually the same person in disguise;
[3] Intermetamorphosis is the belief that people in the environment swap identities with each other whilst maintaining the same appearance;
[4] Subjective doubles as described by Christodoulou in 1978 is the belief that there is a doppelgänger or double of him- or herself carrying out independent actions;
[5] Mirrored-self misidentification is the belief that one's reflection in a mirror is some other person;
[6] 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 false;
[7] Cotard Syndrome is a rare disorder in which people hold a delusional belief that they are dead (either figuratively or literally), do not exist, are putrefying, or have lost their blood or internal organs. In rare instances, it can include delusions of immortality;
[8] Syndrome of delusional companions is the belief that objects (such as soft toys) are sentient beings;
[9] Clonal pluralization of the self, where a person believes there are multiple copies of him- or herself, identical both physically and psychologically but physically separate and distinct.

There is considerable evidence such disorders are associated with disorders of face perception and recognition[1]. However, it has been suggested that all misidentification problems exist on a continuum of anomalies of familiarity, from déjà vu at one end to the formation of delusional beliefs at the other.

[1] Sno: A Continuum of Misidentification Symptoms in Psychopathology - 1994