Stroke And Alzheimer's: A Complex, Dangerous Combination

Alzheimer's disease is the most common type of dementia, caused by clumps of proteins building up in the brain. Vascular dementia, on the other hand, is often caused by a stroke blocking an artery in the brain, though not all strokes lead to vascular dementia. Both conditions are linked, and it is possible to have more than one type of dementia at the same time. This is known as mixed dementia. So, can a stroke make Alzheimer's worse?

Vascular dementia and stroke

Vascular dementia is a general term for a set of conditions caused by brain damage from impaired blood flow to the brain. It is often associated with left-hemisphere stroke, impacting reasoning, planning, judgment, memory, and other thought processes. The onset of vascular dementia depends on the location and size of the damaged brain area.

Vascular dementia can occur when a stroke blocks an artery in the brain, but not all strokes cause vascular dementia. The severity of the stroke and the location of the damage are factors in whether a stroke leads to vascular dementia. Vascular dementia can also be caused by a series of small strokes or "silent strokes", which are so minor that the person affected may not be aware of them.

The risk factors for vascular dementia are similar to those for heart disease and stroke. These include elevated blood sugar, high blood pressure, high cholesterol, and diabetes. These factors can be controlled through medication and lifestyle changes, which can slow the progression of vascular dementia.

Vascular dementia is a common form of dementia, especially in older adults. It is the second most common form of dementia in the United States, after Alzheimer's disease. Research has shown that almost a quarter of people who have had a stroke will go on to develop dementia within three to six months.

There is currently no cure for vascular dementia, but treatments are available to help manage the symptoms. These include medications to lower blood pressure and control blood sugar, as well as Alzheimer's medications in some cases.

Risk factors for vascular dementia

Vascular dementia is caused by impaired blood flow to the brain, which can be the result of a stroke blocking an artery. However, not all strokes lead to vascular dementia. The risk of developing vascular dementia depends on the severity and location of the stroke.

• Age: The risk of vascular dementia increases with age, especially after 65.
• Sex: Men are at a slightly higher risk of developing vascular dementia than women.
• Cardiovascular conditions: People with cardiovascular issues such as high blood pressure, heart disease, or diabetes are at a higher risk. These conditions increase the chances of blood clots or bleeds in the brain's blood vessels.
• Cerebral amyloid angiopathy (CAA): CAA damages the small arteries in the outer regions of the brain, causing them to leak and increasing the risk of bleeding.
• Sleep apnoea: This condition causes temporary breathing cessation during sleep, leading to small blood clots in the brain. It increases the risk of high blood pressure, stroke, heart attacks, and vascular dementia.
• Lifestyle choices: Physical inactivity, smoking, an unhealthy diet, and excessive alcohol consumption can all increase the risk of vascular dementia by worsening cardiovascular health.
• Previous strokes: A history of strokes or mini-strokes (transient ischemic attacks) can increase the risk of vascular dementia by causing brain damage.
• Abnormal aging of blood vessels (atherosclerosis): This condition narrows blood vessels due to plaque buildup, reducing blood flow to the brain.
• High cholesterol: Elevated levels of low-density lipoprotein (LDL), or "bad" cholesterol, are associated with an increased risk.
• High blood pressure: This puts extra stress on blood vessels, increasing the risk of vascular problems in the brain.
• Diabetes: High blood glucose levels damage blood vessels, and diabetes is linked to an increased risk of stroke and vascular dementia.
• Smoking: Smoking directly damages blood vessels and increases the risk of atherosclerosis and other circulatory diseases, including vascular dementia.
• Obesity: Being overweight is a known risk factor for vascular diseases and is likely to increase the risk of vascular dementia.
• Atrial fibrillation: This irregular heart rhythm increases the risk of stroke and vascular dementia by causing blood clots to form in the heart that can travel to the brain.

Stroke survivors with dementia at greater risk of death

Stroke survivors with dementia are at a greater risk of death. The risk of death from strokes has declined, but the number of stroke survivors with cerebral compromise and cognitive dysfunction has increased. Stroke survivors are at an increased risk of cognitive impairment, with about 25% of stroke survivors developing dementia. The risk of dementia after stroke is higher in patients with vascular comorbid conditions, including hypertension, atrial fibrillation, diabetes mellitus, myocardial infarction, and congestive heart failure.

The risk factors for delayed dementia after stroke injury include older age, vascular comorbidities, prior stroke, and pre-stroke impairment. The presence of three or more cardiovascular risk factors increases the risk of dementia or death by fourfold in elderly stroke survivors. The risk of dementia is also higher when vascular comorbid conditions occur together.

The neuroimaging determinants of dementia after stroke include silent brain infarcts, white matter changes, lacunar infarcts, and medial temporal lobe atrophy. Severe white matter changes and medial temporal lobe atrophy as sequelae of ischemic injury are substrates of dementia.

The best way to prevent post-stroke dementia is to prevent stroke recurrence and stroke severity through optimal acute treatment and intensive secondary prevention. Controlling vascular disease risk factors is essential to reduce the burden of cognitive dysfunction after stroke.

Astrocytes and their role in dementia

Astrocytes are highly complex cells that form non-overlapping domains in the brain. They are involved in neuronal support, neurogenesis, and the determination of the micro-architecture of the grey matter. Astrocytes are also key components of the tripartite synapse and the neurovascular unit (NVU), where they are essential for blood-brain barrier maintenance and neurovascular coupling.

Astrocytes play a critical role in the development of dementia, including Alzheimer's disease. Research has shown that astrocytes respond to both neurofibrillary tangles and plaques, which are characteristic features of Alzheimer's disease. This response can be either neuroprotective or deleterious. In the early stages of Alzheimer's disease and other forms of dementia, astrocyte atrophy occurs, leading to disruptions in synaptic connectivity, neurotransmitter homeostasis, and neuronal death through increased excitotoxicity. At later stages, astrocytes become activated and contribute to the neuroinflammatory component of neurodegeneration.

The role of astrocytes in dementia is an active area of research, with ongoing projects aiming to understand their complex responses to pathological changes in the brain. By enhancing the supportive and neuroprotective functions of astrocytes, new therapeutic approaches to dementia may be developed.

Preventing vascular dementia

Vascular dementia is caused by reduced blood flow to the brain, which can be the result of a stroke. While not everyone who has a stroke will develop vascular dementia, it is a significant risk factor. About 1 in 4 or 5 people who have a stroke will develop vascular dementia within three to six months.

Vascular dementia can be prevented by lowering your risk factors for heart disease and stroke. These include:

• Maintaining a healthy blood pressure: Keeping your blood pressure in the normal range may help prevent vascular dementia.
• Prevent or control diabetes: Avoiding the onset of type 2 diabetes with diet and exercise can lower your risk of dementia. Controlling glucose levels if you already have diabetes may help protect your brain blood vessels from damage.
• Quit smoking: Smoking damages blood vessels and increases your risk of circulatory diseases, including vascular dementia.
• Get physical exercise: Regular physical activity can help you avoid vascular dementia.
• Keep your cholesterol in check: A healthy, low-fat diet and cholesterol-lowering medications can reduce your risk of strokes and heart attacks that could lead to vascular dementia.

In addition to the above, a healthy lifestyle can help reduce your risk of developing dementia. This includes:

• Eating a balanced diet
• Maintaining a healthy weight
• Exercising regularly
• Keeping alcohol consumption within recommended limits
• Getting an NHS Health Check if you are aged between 40 and 74

Frequently asked questions