Vascular dementia results from reduced blood flow to the brain, often as a result of a stroke or a series of strokes. Vascular dementia is the second most common form of dementia, and is believed to cause 10 to 20 per cent of cases. Vascular dementia and Alzheimer's disease frequently coexist, and have shared risk factors.
What causes vascular dementia?
Vascular dementia is caused by changes to the brain’s blood vessels that reduce delivery of blood and oxygen to regions of the brain. These changes can arise as a result of:
- stroke, the primary cause of blood flow irregularities leading to dementia
- arteriosclerosis, hardening and loss of elasticity of the walls of arteries, or
- atherosclerosis, build-up of cholesterol and fatty plaques in blood vessels.
Stroke-induced vascular dementia can occur either as a result of several small strokes in different regions of the brain. None of these strokes is necessarily symptomatic immediately, but together over time become enough to cause cognitive deficits.
More commonly, vascular dementia results from a major isolated instance of stroke. The blockage of blood vessels resulting from ischemic stroke prevents oxygen and other nutrients reaching brain regions, which causes neurons to die and produces cognitive deficits.
Symptoms of vascular dementia
While the symptoms of vascular disease are similar to that of Alzheimer's disease, the conditions are distinguishable.
In vascular dementia, the symptoms of the condition depend on the location(s) at which blood flow is impeded. In contrast to Alzheimer's disease, there is no standard pattern or order to the cognitive decline. A stroke that affects the motor cortex will impact motor function, a stroke in the language area of the cerebral cortex will affect speech and comprehension, and strokes in subcortical or prefrontal cortical regions can cause slow thought and poor planning, attention and organisation. These latter symptoms appear to be the most common in vascular dementia, but because of variability in where strokes occur, the lack of such executive control symptoms does not rule out a VD diagnosis.
Risk factors for vascular dementia
Vascular dementia shares many risk factors with Alzheimer's disease. The primary risk factor for both is age.
Risk factors for vascular dementia are also similar to those for cardiovascular disease. These include:
- Hypertension (high blood pressure)
- Insulin resistance, particularly in middle age rather than later life
The fact that Alzheimer's disease shares these risk factors likely indicates that proper nourishment of the brain through healthy intact vasculature is important in staving off Alzheimer's.
Both dementias also have known genetic risk factors, some of which are shared:
- The ApoE4 (apolipoprotein E4) gene, which increases cardiovascular risk
- APP (amyloid precursor protein) gene, which ultimately results in amyloid-β production. Amyloid-β appears to have cardiovascular effects, and in Alzheimer's disease also has neuronal effects as it interacts with tau protein
In addition to these shared genetic risk factors, mutations in a gene called Notch3 appear to increase risk for vascular dementia.