A comparative neuropsychological evaluation of individuals over 65 years of age who present with either very-late-onset schizophrenia-like-psychosis, chronic schizophrenia or a late onset psychotic depression

Widespread cognitive deficits have been consistently associated with psychosis. However there still remains little research examining cognitive deficits in older individuals with psychosis. Moreover there has been little consideration of the potentially different cognitive profiles of elderly individuals with a chronic yet typical onset schizophrenia (Chronically Ill, Typical Onset Schizophrenia: TOS), those of a similar age who had presented with a first-episode of schizophrenia psychosis when 60 years or more (i.e. a Very-Late-Onset Schizophrenia-Like-Psychosis: VLOSLP), and older individuals who had presented with a first-episode of psychotic depression when 60 years or more (i.e. a Late-Onset Psychotic Depression: LOPD). Existing research has utilised either limited cognitive screening tools, or abbreviated neuropsychological batteries, thus limiting comprehensive cognitive profiling of these populations. The primary research objective of this Doctoral thesis is to better characterize the cognitive profile of elderly individuals with VLOSLP. The second objective is to compare and contrast the cognitive profile of this VLOSLP group with that of both a similarly aged elderly TOS group and LOPD control group. The general clinical aim is to identify any specific cognitive challenges for elderly individuals with a schizophrenia psychosis. Twenty-five individuals with VLOSLP, 27 individuals with TOS and 18 individuals with a LOPD completed a comprehensive neuropsychological battery assessing various domains including attention, working memory, motor speed and speed of information processing, learning and memory, and executive functioning. Demographic information and clinical and social functioning measures were also collected. The results indicated that individuals with VLOSLP showed a wide range of performance across the domains from within the average range to within the impaired range. Analyses of group differences revealed that the LOPD group performed significantly better than the two schizophrenia groups, and within the average range on the majority of cognitive domains assessed. The cognitive profiles of the two elderly schizophrenia groups were similar across the majority of domains, with the performance of the VLOSLP group being somewhat better overall than that of the elderly early-onset group, albeit not significantly so. Given the wide range of performance noted in the VLOSLP group, exploratory cluster was conducted and identified two statistically distinct Clusters. Follow-up comparisons of these two Clusters and the TOS group revealed that one Cluster’s neuropsychological performance was similar to that of the TOS group, demonstrating widespread cognitive impairments, and with subtle indications of slightly greater impairment. The other Cluster presented with largely intact cognitive performance. These preliminary findings raise more questions than answers. The first is whether only some individuals with a VLOSLP present with a classic schizophrenia illness characterised by widespread cognitive impairment consistent with TOS. The second is why this illness appears to cause greater cognitive impairment in this subset than seen in TOS. Alternatively, does this subset show the signs of an early neurodegenerative dementing condition, distinct from schizophrenia? Future longitudinal studies will be needed to answer these questions.