脳血管障害に基づく認知機能障害の病態

抄録

Insufficiencies of blood supply will more or less lead to brain dysfunction. Cognitive impairment caused by such cerebrovascular insufficiency was called vascular cognitive impairment (VCI), a clinical syndrome composed of a markedly heterogeneous group of diseases rather than a unique pathological process. It includes large vessel disease with strategic single or multiple strokes and small vessel disease with progressive damage to the basal ganglia and/or the white matter. VCI was previously believed to be distinct from Alzheimer’s disease (AD) resulting from a neurodegenerative process. However, such simple dichotomy needs to be reconsidered in light of the shared features between AD and VCI: these two disorders increase in prevalence with age, frequently occur concomitantly, and considerably overlaps in their symptomatology, pathophysiology, and comorbidity. So-called ‘mixed’ brain pathologies, mainly comprising of AD pathology and cerebral infarctions, are reported to account for most dementia cases in community-dwelling elderly people. Consistent with this notion, the contributors to attributable risks at death for dementia include small vessel disease and multiple vascular pathologies, which are no less than those of the main pathological hallmarks of AD, neocortical neuritic plaques and neurofibrillary tangles. Importantly, the multifactorial aspects of cognitive impairment have been incorporated in the dynamic polygon hypothesis, which takes into account the contributions of strokes of all sizes and white matter hyperintensities in parallel to those of plaques and tangles. In terms of the treatment of dementia, it is undoubtedly important to control vascular risk factors for the prevention of VCI. However, even in patients who have AD without cerebrovascular disease, treatment of vascular risk factors is associated with a slower decline in the Mini-Mental State Examination score. Therefore, physicians should always bear in mind that vascular risk factors need to be controlled to achieve a reduction in the risk of dementia, even if the dementia is caused by AD.