Brayne, Carol Elspeth Goodeve; (1991) A study of dementia in a rural population. Doctoral thesis (M.D), UCL (University College London).

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Abstract

Dementia, in particular Alzheimer's disease, has been widely investigated in clinical settings. Moreover, many epidemiological studies have been carried out to estimate the prevalence and incidence of dementia and, less frequently, Alzheimer's disease. There have also been studies of ageing cohorts to examine mental changes associated with ageing. There has, however, been little research on unselected elderly populations which has been detailed enough to examine the relationship between normal and abnormal mental ageing. The aim of this study was to investigate the distribution of the indices of dementia in a rural population. This allowed investigation of the hypothesis that variables associated with dementia, in particular Alzheimer's disease, are distributed bimodally in the population and allowed investigation of possible associations with these distributions. It also provided prevalence estimates of dementia in a rural population. A population sample of women aged 70 to 79 was selected from a rural Cambridgeshire health centre. Using the Cambridge Examination for Mental Disorders in the Elderly all aspects required for the diagnosis of dementia and tentative differential diagnosis were collected on 365 women. There was no evidence of bimodality in any of the derived scales, whether cognitive, behavioural or ischaemic. The prevalence of dementia of all types and levels, including mild, was 4.3% in the 70 to 74 age group and 11.7% in the 75 to 79 age group. For more severe dementia a prevalence of 2.8% was found in the 75 to 79 age group, and 0% in the 70 to 74 age group. The rates for more severe dementia were lower than other recent prevalence studies in the UK, whereas the rates for all levels of severity were higher. The tentative diagnosis of Alzheimer's disease accounted for 52% of the diagnoses of dementia and multi-infarct dementia for 31%. Age, social class and education were all significantly and independently associated with scores on the longer cognitive scales (Mini-Mental State Examination and the CAMCOG scale of CAMDEX). Risk factors suggested in the literature for dementia, Alzheimer's disease and cognitive impairment was also investigated. Few factors were associated with either cognitive function or dementia. Age was the only variable associated with both cognitive function and the diagnosis of dementia. Only small proportions of the population were exposed to postulated risk factors and these risk factors, if proven, would account for little population excess risk. In this study no significant separation of performance on cognitive or behavioural scales between the demented and the non-demented was found. This could have been due to the small numbers in the tails of the frequency distributions but, if true, it is suggested that this observation might be related to the continuous distribution of underlying neuropathological lesions, such as plaques and tangles, noted in autopsy series of unselected populations. If so, current research into the mechanisms of the dementias may have implications for the understanding of cognitive decline noted in the non-demented elderly over time.

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