Vascular Dementia


English: PET scan of a human brain with Alzhei...

English: PET scan of a human brain with Alzheimer’s disease.

Global prevalence of dementia is expected to increase exponentially over the next 40 years with the changing demographics and increase in the number of older people.

Dementia is defined as a decline in cognitive function of sufficient severity to interfere with usual daily functioning. Memory loss is prominent among the features and depending on the cause you can have impairment in judgement, thinking and language recognition.

There are three types of dementia Alzheimer’s disease, vascular dementia, and a mixed variant of the two.

Alzheimer’s Diagnosis

Neuropathological classification of Alzheimer’s disease depends on the identification of beta-amyloid plaques, amyloid angiopathy, and neurofibrillary tangles of hyperphosphorylated tau protein. The predominant hypothesis underlying its pathogenesis is the amyloid cascade hypothesis.

The sporadic form of Alzheimer’s Disease is the most common cause, and is largely due to the accumulation of dead amyloid in the brain. In the rarer genetically inherited form, the accumulation is either due to diminished removal of amyloid from the brain or to increased amyloid production. The result of the pathology is severe damage to cortical circuitry of the brain areas responsible for memory and language.

Vascular Dementia

Vascular dementia in its purist form represent about 18% to 20% of all causes of dementia. There is a large spectrum of mixed dementia, which can result from single or multiple strategic infarcts.

The hippocampal area affected by Alzheimer’s disease is also extremely vulnerable to ischaemic incidents. It can be damaged if there is an ischaemic incident within the territory of the hippocampus, but it can also occur with distal or distant ischaemic incidents.

CVD Risk Factors

Cardiovascular risk factors pose significant risks for vascular dementia and are significant risk factors for Alzheimer’s disease.

There is increasing evidence vascular pathology plays a role in dementia. Midlife hypertension seems to be critical, and perhaps later life cerebral hypoperfusion also. There is a less persistent risk seen in those whose hypertension persists later in life.

Functional Impairment

Studies using functional impairment as an endpoint are more robust than using cognitive impairment. The Kungsholmen project, a cross-sectional study that looked at 1,600 patients aged over 75, showed a blood pressure less than 140/75 was associated with a higher prevalence of Alzheimer’s disease and dementia. The Chicago Health & Aging Project identified risk with a blood pressure of less than 130/70. The longitudinal study, Gothenburg H70, followed 182 people over 15 years and looked at blood pressure as a continuous variable. People with lower blood pressure were found to be at greatest risk. The East Boston Study and the Bronx Ageing Study showed that patients with lower blood pressure and on anti-hypertensives were at higher risk of developing Alzheimer’s disease and dementia relative to those with higher blood pressures also being treated.

Previous research has shown that the prevalence of neurocardiovascular instability is about 70% in those with cognitive impairment. Neurocardiovascular instability refers to a spectrum of conditions including orthostatic hypotension, carotid sinus hypersensitivity and autonomic failure.

Does Hypotension Cause Complications?

Orthostatic hypotension is especially prevalent in diffuse Lewy body and Parkinson’s disease dementia, but it is also more common in patients with Alzheimer’s disease and vascular dementia than it is in non-demented elderly individuals. Autonomic dysfunction is found in different types of dementia, particularly in Parkinson’s disease and diffuse Lewy body dementia, as is carotid sinus hypersensitivity, although it is also strongly associated with Alzheimer’s disease

The drop in blood pressure seen in orthostatic hypotension is associated with cognitive impairment. Cerebrovascular autoregulation is severely impaired in these people and they are more likely to have episodes of cerebral hypoperfusion.

Patients with dementia often report with typical symptoms of hypotension such as dizziness. They are far less sensitive to orthostatic symptoms and may not present until they have actually had a fall or syncopal episode.

Conclusion

In conclusion, with ageing, blood pressure tends to decrease, and the necessity of blood pressure reducing antihypertensives should be reviewed. There is an evolution of blood pressure changes that occur with the progression of dementia.

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