Cardiovascular factors in Alzheimer's disease

Cardiovascular factors in Alzheimer's diseaseThe traditional assumption that there are two distinct forms of dementia-vascular dementia and Alzheimer's disease-respectively with and without evidence of vascular disease as a presumed causative factor, has been called into question by recent epidemiological evidence which raises the possibility that vascular risk factors may be important in the aetiology not only of dementia in general but also specifically for Alzheimer's disease.This editorial summarises these epidemiological findings and considers possible methods of pathogenesis. Methodological issuesThe historical distinction between the vascular dementias and Alzheimer's disease is a major obstacle in assessing the role of vascular disease as a risk factor for Alzheimer's disease.Defining a condition according to its presumed aetiology can preclude a critical examination of risk factors included or excluded by that definition.Research criteria such as NINCDS-ADRDA, 1 emphasise Alzheimer's disease as a diagnosis of exclusion particularly with regard to vascular disease, therefore any association between the two will be underestimated through selective classification.The increased use of imaging techniques may cause additional confusion-namely, what bearing should evidence of subclinical cerebrovascular disease (known to be common in older populations) have on the diagnosis?However, failing to assess subclinical cerebrovascular disease in this way limits the conclusions that can be drawn from any association found between vascular risk factors and clinical Alzheimer's disease, an important issue being whether such an association is mediated by an eVect on Alzheimer's pathology or by cognitive impairment secondary to increased cerebrovascular disease in the context of "mixed dementia".Given high rates of mixed Alzheimer's and cerebrovascular pathology at postmortem examination, 2 a diagnostic system which attempts to subdivide dementia into mutually exclusive categories is of limited usefulness in assessing the role of disease processes which may aVect both.The problem of subclinical disease complicates the assessment not only of dementia as the outcome variable but also of vascular disease as the exposure.A history or not of cardiovascular events is an inadequate reflection of underlying vascular disease just as reported hypertension or diabetes may not reflect measured blood pressure or glucose tolerance and studies which rely on reported diagnoses in unscreened populations may underestimate associations between Alzheimer's disease and covert vascular disease.This situation is compounded by the important proportion of subjects who will die from vascular disease before dementia becomes apparent.