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

OBJECTIVES: Psychosis of Alzheimer's disease (AD) may represent a distinct disease phenotype; however, neuropsychological profile and neural basis linked to this phenotype have not yet been clarified. In this study, we aimed at detecting whether impairment in specific cognitive domains predicts the onset of psychosis in AD patients and what grey matter alterations, their location, and the rate of atrophy are associated with psychosis of AD.
METHODS: Longitudinal neuropsychological data from AD patients with and without psychosis were analysed to determine whether the neuropsychological profile can predict the onset of psychosis. A voxel-based morphometry (VBM) on longitudinal T1-weighted images was used to explore differences in grey matter volume and in the rate of atrophy between groups.
RESULTS: Noncognitive domain predicted the psychosis onset. However, AD patients with psychosis exhibited greater atrophy in the right anterior-inferior temporal lobe, including the fusiform gyrus (cluster-p-family-wise error [pfwe] < 0.05; peak-p uncorrected [pUNC] < 0.001) as well as greater rate of atrophy in the right insula than nonpsychotic patients (cluster-pFWE = 0.075; peak-pUNC < 0.001). The anterior-inferior temporal lobe is part of the ventral visual stream, and the insula plays a key role in the salience network.
CONCLUSIONS: This finding suggests that damage in these areas underpins an impairment in the visual processing of the objects and an impairment in the attribution of salience to the misperceived stimuli, which in turn leads to the onset of psychosis. These findings tie in well with the neuropsychological model of psychosis, according to which the simultaneous presence of two factors, namely misperception and misattribution, underlies psychosis in dementia.