The emergence of delusional companions in Alzheimer's disease: An unusual misidentification syndrome

Introduction. Misidentifications in the course of organic diseases, including Alzheimer's disease (AD), have been associated with right sided brain dysfunction. The reasons for this association might be clarified by investigating the contribution of neurobiological, cognitive and emotional factors to distinctive types of misidentification. Methods. This study reports the cases of three patients with AD presenting a novel misidentification delusion in which objects with intrinsically comforting associations, soft toys, were experienced as sentient and triggered associated behaviours. Investigations included regional cerebral blood flow (rCBF) measurements with HMPAO SPECT and a comprehensive clinical and neuropsychological assessment. Results. All three patients showed a distinctive pattern of rCBF with dysfunction centred in the right parietal area and severe visuospatial and visuoperceptive processing deficits, with relatively preserved memory and language abilities. Conclusion. These findings support the hypothesis that this type of misidentification delusion may be facilitated by right sided regional brain dysfunction involving visuoperceptual processing. Other historical and cognitive data from these patients suggests that the appearance of the symptom may be determined by the coexistence of a more widespread disorder of reality processing, which interacts with cognitive and psychogenic factors.