The delusional misidentification syndromes: strange, fascinating, and instructive.

The delusional misidentification syndromes (Capgras' syndrome, Frégoli syndrome, intermetamorphosis syndrome, syndrome of subjective doubles) are rare psychopathologic phenomena that occur primarily in the setting of schizophrenic illness, affective disorder, and organic illness. They are grouped together because they often co-occur and interchange, and their basic theme is the concept of the double (sosie). They are distinguished as hypoidentifications (Capgras' syndrome) and hyperidentifications (the other three syndromes). In this review, we present the basic hypotheses that have been put forward to explain these syndromes and propose that the appearance of these syndromes must alert physicians to investigate the existence of possible organic contributions.