Cognitive phenotype of psychotic symptoms in Alzheimer's disease: evidence for impaired visuoperceptual function in the misidentification subtype

Abstract

BackgroundEstablishing the cognitive phenotype of psychotic symptoms in Alzheimer's disease (AD) could localise discrete pathology and target symptomatic treatment. This study aimed to establish whether psychotic symptoms would be associated with poorer performance on neuropsychological tests known to correlate with striatal dopaminergic function and to investigate whether these differences would be attributed to the paranoid (persecutory delusions) or misidentification (misidentification phenomena +/− hallucinations) subtype.MethodsSeventy patients with probable AD (34 psychotic and 36 nonpsychotic) were recruited to the study. Analysis of covariance was used to compare motor speed and the rapid visual processing test of sustained visual attention, after adjusting for potential confounding factors. Multivariate analyses were used to compare performance across other cognitive domains. Significant findings were explored by separating patients on the basis of subtype.ResultsRapid visual processing performance accuracy was reduced in patients with psychotic symptoms (F 1,58 = 5.94, p = 0.02) and differed significantly across subtypes (F 2,51 = 3.94, p = 0.03), largely because of poorer performance in the misidentification compared with nonpsychotic group. Multivariate analyses (corrected for multiple comparisons) showed poorer performance on the incomplete letters task in psychotic patients (F 1,63 = 8.77, p = 0.004) and across subtypes (F 2,55 = 10.90, p < 0.001), similarly attributed to the misidentification subtype.ConclusionsThese findings provide further support of the involvement of dopaminergic networks in the psychosis endophenotype in AD and, in addition, implicate the ventral (temporo‐occipital) pathway in the misidentification subtype. Future studies should investigate the early trajectory of neuropathological change in vivo across psychosis subtypes.© 2015 The Authors. International Journal of Geriatric Psychiatry published by John Wiley & Sons, Ltd.

Psychosis of Alzheimer's disease: Neuropsychological and neuroimaging longitudinal study

“…This is in keeping with the observation that most patients in our sample had misidentification psychotic symptoms, either alone or combined with paranoid symptoms. Indeed, the misidentification subtype seems to be associated with a greater impairment in visuo‐perceptual tasks such as figural completion, which is assessed in the Visual Object and Space Perception Battery and results above all from damage in the brain networks involved in object processing . Moreover, we found a higher rate of atrophy in the insula, which is part of the cortical salience network.…”

“…Psychosis was investigated as a patient's trait and not as patient's state. This approach has been used in previous studies on AD psychosis and is consistent with a continuum model of psychosis . Patients were coded as non‐psychotic (AD) if psychotic symptoms were not present either at the baseline or at any of the follow‐up examinations during the observation period.…”

Lack of Early Improvement with Antipsychotics is a Marker for Subsequent Nonresponse in Behavioral and Psychological Symptoms of Dementia: Analysis of CATIE-AD Data

“…paranoid, misidentification, mixed, and non-psychotic). This categorization was based on factorial analysis of NPI delusions and hallucinations domains, 24,25 which identified two factors: a ‘paranoid’ subtype (delusions of persecution and/or abandonment); and a ‘misidentification’ subtype (misidentification phenomena and/or hallucinations). Patients who were experiencing both types of symptoms were described as ‘mixed’.…”

An unusual delusion of duplication in a patient affected by Dementia with Lewy bodies

“…In this context, there is a clear evidence for impaired visuoperceptual functions in the appearance of misidentificative psychotic symptoms in patients affected by Alzheimer's disease [20]. …”