Vascular dementia: a construct in evolution.

Since the late 1800s, when Alzheimer and Binswanger proposed the concept of "arteriosclerotic brain degeneration," there has been an evolution in thinking regarding cerebrovascular disease (CVD) as a basis for dementia. While later work recognized the importance of specific infarct characteristics including volume, multiplicity, and location, recent studies have found that many factors may work in combination with those characteristics to produce dementia, including white matter disease; vascular risk factors such as diabetes; comorbid illnesses, particularly those that might produce cerebral ischemia or hypoxia; genetic factors; and host characteristics such as older age and fewer years of education. Studies of the prevalence of vascular dementia (VaD) have suggested that CVD is second only to Alzheimer's disease as a basis for dementia in Western countries and the most common basis in certain Asian countries, but those studies may have underestimated the frequency of dementia associated with CVD due to a failure to perform brain imaging and decreased survival among patients with CVD. Few studies of the incidence of VaD have been performed, but they have also consistently demonstrated an elevated risk associated with CVD. While certain methodologic issues have contributed to the debate regarding the importance of CVD as a basis for dementia, including variability in the techniques that have been used to characterize brain lesions, assess cognitive function, and diagnose dementia; difficulties inherent in the determination of a causal role for CVD in dementia; and the potential confounding effects of aphasia and depression in patients with stroke, it is clear that VaD remains an important public health problem.