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.

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• The Capgras delusion is the belief that (usually) a close relative or spouse has been replaced by an identical-looking impostor.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:

• 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.
• 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 versions of him or herself in existence⁴.

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

References

1. Ellis, H.D.; Luauté, J.P.; & Retterstol, N. (1994). (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=7846223&dopt=Abstract) Delusional misidentification syndromes. Psychopathology 27 117–120.
2. Benson, D.F.; Gardner, H.; & Meadows, J.C. (1976). (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=943070&dopt=Abstract) Reduplicative paramnesia. Neurology 26 (2) 147–151.
3. Shanks, M.F. & Venneri, A. (2002). The emergence of delusional companions in Alzheimer's disease: An unusual misidentification syndrome. Cognitive Neuropsychiatry 7 (4) 317–328.
4. Voros, V.; Tenyi, T.; Simon, M.; & Trixler, M. (2003). (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12679592&dopt=Abstract) 'Clonal pluralization of the self': a new form of delusional misidentification syndrome. Psychopathology 36 (1) 46–48.
5. Sno, H.N. (1994). (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=7846229&dopt=Abstract) A continuum of misidentification symptoms. Psychopathology 27 (3–5) 144–147.

See also

• Cognitive neuropsychiatry
• Delusion
• Face perception