The Overlap Between Vascular Disease and Alzheimer's Disease
The flexibility and structural integrity of blood vessel networks declines with age. Metabolic waste products accumulate in blood vessel walls, and separately a combination of damaged cells, damaged proteins, and chronic inflammation leads to harmful restructuring. Other mechanisms are at work also, such as those involved in hypertension. This all means that ever more tiny blood vessels fail in one way or another, either bleeding into brain tissue or not delivering oxygen efficiently. The resulting damage builds up, a bit at a time. Thus there is every reason to consider a causal link between vascular issues and forms of dementia such as Alzheimer's: vascular problems eating away at the brain's integrity are going to worsen the effects of an emerging dementia even if it is caused by entirely different mechanisms. Further, there is the possibility that issues with blood flow in the brain can directly impact clearance of the misfolded proteins called amyloids implicated in the progression of Alzheimer's disease. Other links may yet be discovered.
The interaction between cerebrovascular disease (CVD) and Alzheimer's disease (AD) is a topic of considerable current interest. With age there is an increasing prevalence of coincident AD and CVD that is well recognized. Since 50% to 84% of the brains of persons who die aged 80 to 90+ show appreciable cerebrovascular lesions (CVL), a specific problem is their impact in relation to AD pathology. CVD frequently occurs in brains of both non-demented elderly and AD patients. The burden of vascular and AD-type pathologies are leading and independent causes of dementia in the elderly, suggesting additive or synergistic effects of both types of lesions on cognitive impairment.The most frequent vascular pathologies in the aging brain and in AD are cerebral amyloid angiopathy and small vessel disease. AD brains with minor CVD, similar to pure vascular dementia, show subcortical vascular lesions in about two-thirds, while in mixed type dementia (AD plus vascular dementia), multiple larger infarcts are more frequent. Small infarcts in patients with full-blown AD have no impact on cognitive decline but are overwhelmed by the severity of Alzheimer pathology, while in early stages of AD, cerebrovascular lesions may influence and promote cognitive impairment, lowering the threshold for clinically overt dementia.