Introduction

The presence of cerebrovascular disease and vascular risk factors are generally considered to be exclusion criteria for the clinical diagnosis of Alzheimer's disease (AD). The high prevalence of cerebrovascular disease and AD in the elderly population means that the category of patients with dementia, stroke and vascular dementia, includes patients with AD. The criteria used to diagnose AD were established by consensus, with vascular abnormalities becoming an artificial border between vascular dementia and AD. However, growing evidence suggests that the distinction is not clear cut. Half of all patients with vascular disease who become demented also have AD and a third of patients with pathologically confirmed AD have evidence of vascular lesions. Brain infarcts may play an important role in determining the presence and severity of clinical symptoms of AD. Data from large population studies give validity to the construct of mixed AD/vascular dementia. It is not known whether the cerebral vascular pathology found in the brains of patients with AD is coincident or causal. Is there a direct interaction between the two pathological processes? Alternatively, does cerebrovascular disease unmask subclinical AD? Data supporting both arguments exist. The puzzle remains. Understanding the interaction between cerebrovascular and neurodegenerative disorders demands a radical shift in framework and thought process.

Coexistence of AD and vascular pathology

Several longitudinal studies have demonstrated that the changes of cerebrovascular disease and neurodegeneration with Alzheimer-type pathology have synergistic effects on cognition.