Mirrored-self misidentification: Two cases of focal onset dementia

We present two patients in whom the mirror sign, the inability to recognize one's own reflected image, was a stable and persisting symptom signalling the onset of a progressive dementing illness. Extensive neuropsychological testing was conducted with both patients, with particular emphasis on face processing and the understanding of reflected space. Both patients were als o investigated with structural imaging techniques (computed tomography and magnetic resonance imaging). Although the neuroimaging results were not str ongly lateralizing for either patient, neuropsychological testing revealed striking right hemisphere dysfunction with relatively intact left hemispher e cognitive function in both patients. Of particular interest was the patie nts' dissociation on tests of face processing; one patient, FE, had signifi cant face processing deficits while the other patient, TH, had relatively i ntact face processing. Further testing with TH revealed striking deficits i n his ability to interpret reflected space. The results of the face process ing tests are discussed in the context of current models of normal face pro cessing, with particular emphasis on the affective component in face recogn ition. We propose that a combination of cognitive deficits underlie the mir ror sign delusion, including perceptual, affective and reasoning impairment s, and also discuss the contributions of cortical and subcortical lesions i n these two patients and in delusions in general.