From strokes to dementia, diseases of the nervous system are the leading cause of disability-adjusted life years. This calls for strong preventive strategies to be incorporated into universal health coverage
By Vladimir Hachinski, professor of neurology and epidemiology at Western University
Diseases of the nervous system represent the leading cause of disability- adjusted life years, with stroke and dementia accounting for more than half of the total, at 42% and 10%, respectively.
Strokes result from a sudden blockage or rupture of a brain artery. The extent of the damage varies, depending partly on the cause: atherosclerosis, hardened arteries, high blood pressure or blood clots from the heart that block brain arteries.
Dementia means severe impairment of thinking, memory and other abilities, resulting in dependency.
Two pathologies account for the majority of cases of dementia: Alzheimer pathology, characterised by senile plaques and neurofibrillary tangles and cerebrovascular (blood vessel) pathology. The main types result from:
- Large arteries, where abnormal depositions of fats and other materials (atherosclerosis) narrow the walls of the larger arteries and become breeding grounds for blood clots that can occlude blood vessels either locally or downstream;
- Small arteries, where the walls are thickened and weakened, usually due to high blood pressure, leading to closure and producing death of the tissue supplied by the artery (ischemic infarct) or rupture (brain haemorrhage); or
- Heart abnormalities, which can also lead to clot formation that can be washed into the brain circulation and cause brain infarcts.
Atrial fibrillation (an irregular heart beat) represents the leading cause of stroke and a risk factor for dementia. In some low- and middle-income countries, rheumatic heart disease also contributes to the risk of stroke. The mainstay treatment of both atrial fibrillation and rheumatic heart disease is anticoagulation – thinning the blood enough to prevent clot formation but not enough to cause bleeding. Anticoagulation requires close supervision, only possible at the population level by a universal health coverage system.
The older the person, the more likely both pathologies contribute to the dementia. So far, vascular pathology is the only treatable and preventable one. This forms the scientific basis for preventing stoke and dementia together.
A stroke doubles the chances of developing dementia, but fortunately, stroke is 90% preventable and dementia is preventable by at least one third (see table 1). In addition to exercise and a healthy diet, patients require control of risk factors such as high blood pressure, cholesterol and atrial fibrillation that involve medication and continuing health care.
Universal health coverage represents the essential framework for delivering such care.
Air pollution has been known to impair the lungs, hurt the heart and predispose to stroke. More recently, it also has been shown to increase the risk of dementia (see table 2).
The closer people live to a major highway the higher the risk of developing dementia.
Air pollution represents a vital example of the importance of a healthy environment for overall health, particularly brain health. Without it, the World Health Organization’s definition of health – a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity – cannot be fulfilled.
At the individual level, prevention strategies have emphasised information. These are an essential first step. However, motivation and implementation also play crucial roles. Without universal health coverage, implementation becomes very difficult.
With a population of 14 million, the Canadian province of Ontario illustrates what is possible when universal care coverage is available. In 2000 the province introduced a strategy of building stroke units, stroke prevention clinics and carrying out public campaigns on risk factor controls. These strategies aided in reducing the incidence of stroke by 32% and decreasing the incidence of dementia by 7%.
Based on such evidence, the World Stroke Organization updated its World Stroke Day Proclamation calling for the joint prevention of stroke and potentially treatable dementias.
It has been endorsed by all the major international organisations dealing with the brain, the heart, stroke and dementia (see table 3).
The World Health Summit has featured this approach in the past two years. The 2018 summit was preceded by a one-day symposium on preventing dementia by preventing stroke. This yielded the Berlin Manifesto on the joint prevention of stroke and dementia, available for use by the public and policymakers.
We are undertaking a Canada-wide detailed survey of dementia and stroke focusing on the environment, economic, social, psychological and individual predisposing and protective risk factors.
We plan to develop cost-effective modules that could be implemented in low-, middle- and high-income settings.
The bad news, however, is that diseases of the nervous system have become the leading cause of disability-adjusted life years. The good news is that more than half the incidence of stroke and dementia is potentially preventable.