The comparative neuropsychology of dementia

Abstract

On the basis of neuropathological, neurochemical, genetic, and clinical profile studies on patients, distinct forms of dementia, such as dementia with Lewy bodies (DLB), have been distinguished which were originally thought to be Alzheimer's disease (AD). Dementia with Lewy bodies is probably the second most common form of dementia in the elderly. In this thesis, a well characterised and investigated cohort of DLB and AD patients were compared to non-demented elderly controls in order to establish profiles of cognitive decline in these groups. Initially, comprehensively matched experimental groups were compared using the Cambridge Neuropsychological Test Automated Battery (CANTAB). The DLB group was less impaired than the AD group on a test of visual pattern recognition memory. However, the DLB group performed worse on a number of cognitive tests. Comparison of larger, carefully matched, experimental groups using the Cognitive Drug Research Computerised Assessment Battery (CDR) also revealed differences in the profile of cognitive impairment in DLB and AD. The DLB group showed more marked deficits in attentional abilities than the AD group. In particular, the DLB group were unable to sustain attention. Conversely, the DLB group were less impaired on a test of visual secondary recognition memory than the AD group. Further division of the DLB group into cases with and without persistent visual hallucinations revealed distinct patterns of cognitive impairment in these two groups. Generally, DLB cases with persistent visual hallucinations showed greater attentional and spatial working memory deficits than the DLB cases without persistent visual hallucinations. A final study compared decline in cognitive function over 1 year in DLB, AD and control groups. Similar rates of cognitive decline were identified in a number of cognitive domains in AD and DLB groups. In addition, disproportionate decline in the ability to sustain attention was identified in the DLB group. A comparative model relating known neuropsychological, neurochemical, and neuropathological features of DLB and AD was proposed.