Delusional misidentification syndrome is an umbrella term … for a group of four delusional disorders that occur in the context of mental and neurological illness. They are grouped together as they often occur simultaneously or interchange, and they display the common concept of the double (sosie). They all involve a belief that the identity of a person, object, or place has somehow changed or has been altered. [Author] Christodoulu further categorized these disorders into those including hypo (or under)-identification of a well-known person (Capgras delusion), and hyper (or over)-identification of an unknown person (the remaining three). As these delusions typically only concern one particular topic, they also fall under the category called monothematic delusions.

Interesting!