Introduction Dementia is a public health problem, particularly affecting those over age 80 (Evans et al., 1989; Hebet et al., 2001). While Alzheimer's disease (AD) is the most common cause for dementia among older individuals (Evans et al., 1989; Sayetta 1986), the lifetime risk for stroke equals and may exceed the risk of AD in some circumstances (Seshadri et al., 2006). In addition, MRI evidence of asymptomatic cerebrovascular disease (CVD) occurs in one-third of older individuals (DeCarli et al., 2005). It is, therefore, not surprising that concurrent CVD is often seen in older dementia patients even though they may have a slowly progressive dementing illness most consistent with AD (Mungas et al., 2001b). Although research in this area is ongoing, the impact of clinically silent CVD on cognition and the interaction between CVD and AD processes remains incompletely understood. In this chapter, we discuss the potential role that vascular risk factors and asymptomatic CVD may have on lifetime risk for dementia. In particular, we hypothesize that asymptomatic CVD – in contrast to stroke or other forms of symptomatic CVD – acts as a susceptibility factor for the expression of dementia, most commonly due to AD. Vascular cognitive impairment defined As our understanding of the relationship between vascular disease and cognition continues to evolve, so does our terminology. In this light, vascular dementia (VaD) is now considered to be the extreme end of a spectrum of syndromes of vascular cognitive impairment (VCI) (Hachinski, 1992).
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