Approaching delusional misidentification syndromes as a disorder of the sense of uniqueness.

Co-occurrence of the different types of delusional misidentification syndromes (DMS) implies a common pathogenetic substrate. Until now, theoretical explanations have strained to produce a collective approach, but have been trammeled by the initial definition of the syndromes (Capgras/Fregoli) that originated from the attribution of causal significance to the element of familiarity towards the misidentified object. In this article, we present two cases illustrating the co-occurrence of the syndromes and we attempt to propose a new approach to DMS. We hypothesize that a common potential pathogenetic factor underlying DMS could be a disorder of the sense of uniqueness. The ability to attribute uniqueness to the self and to surrounding people, objects, or places is a principal property of the adaptable mind that acts as a matrix for the identification process. We propose that although the term 'identity' encompasses the concept of uniqueness, this must be accomplished somewhere in a model of semantic processing of identity. Our approach is questioning the current view that this sequential stage is the PIN stage in the functional model of face recognition by Bruce and Young, and we attempt to see the disordered sense of uniqueness within the evolved form of the model of face recognition and delusional misidentification introduced by Ellis and Lewis. We propose that such a disturbance could result in an unstable identification process, vulnerable to discrepancies in perceptual, emotional, or memory input caused by psychotic or organic mental states, thus resulting in a breakdown of the identification process that inevitably leads to a delusion of denial of identity, or to a delusion of 'doubles'.