The Neuropsychological Profile and Phenomenology of Late Onset Psychosis: A Cross-sectional Study on the Differential Diagnosis of Very-Late-Onset Schizophrenia-Like Psychosis, Dementia with Lewy Bodies and Alzheimers Type Dementia with Psychosis

Late onset psychosis not only occurs as a prodromal symptom to neurodegeneration, but it can also be associated with a non-progressive mild cognitive deficit. Studying the phenomenology of psychotic symptoms and the neuropsychological profile may serve as sensitive and non-invasive tools for differential diagnosis. We compared 57 individuals with very-late-onset schizophrenia-like psychosis (VLOSLP), 49 participants with Dementia with Lewy Bodies (DLB) and 35 patients with Alzheimers type Dementia and psychosis (AD+P) concerning the phenomenology of psychotic symptoms and the neuropsychological profile using several measures of cognitive function in a cross-sectional study. Participants with DLB exhibited more visual hallucinations, especially those involving animals, and less partition/paranoid delusions than both other groups. VLOSLP showed more partition delusions and auditory hallucinations of human voices than both other groups. Hence, patients with DLB and VLOSLP showed greater dissimilarity in the phenomenology of psychosis, whereas individuals with AD+P held an intermediate position. Processing speed and executive function were comparably impaired among the three groups, as was expected considering a common underlying set of neurobiological abnormalities for psychosis. However, AD+P showed more strongly reduced learning and consolidation skills, whereas DLB was associated with prominent visuoconstructive deficits. Phenomenology of psychosis may prove especially informative when comparing individuals with DLB to those with VLOSLP. Neuropsychological profiles are able to further aid differential diagnosis of the three groups.