Delusional misidentification of persons in dementia.

The misidentification of a familiar person or of oneself may occur as a complication of dementia. Seven patients experienced alterations of the sense of familiarity for a familiar object or place, for the misidentified person in a novel role, for personal characteristics, or for unfamiliar events as familiar. Five of these had persecutory delusions. These cases suggest that person misidentification in dementia begins with an altered sense of familiarity for a familiar person from a mismatch of new perceptions with past memories. They are sustained by paranoid elaboration or confabulatory rationalisation of a double.