Central nervous system 2 – neurodegenerative and acquired disorders
- • Introduction to neurodegenerative and acquired brain disorders
- • Strokes, and their impact on oral hygiene and oral health
- • Neurodegenerative disorders and their impact on oral health
- • Multiple sclerosis
- • Be aware of the impacts that acquired and neurodegenerative brain disorders may have upon oral hygiene and oral health
- • Be aware of the importance of good preventive care for patients with acquired and neurodegenerative brain disorders
- • Be aware of the importance in involving caregivers in order to improve patients’ oral hygiene and oral health
- • Be aware of the care that needs to be exercised in terms of managing these patients in the dental clinic
Given optimal conditions, the human brain can function very effectively for over 100 years. However, in order to achieve this, the delicate neurons need to be physically and functionally protected. Physical protection of the brain is provided by the bony cranium, the meningeal membranes, as well as the buoyancy afforded by the cerebrospinal fluid. In addition, the cerebrospinal fluid, together with the blood-brain barrier, provides a very protected, stable environment for neuronal function. The brain also receives approximately 20% of cardiac output, ensuring a constant supply of blood glucose and oxygen to meet its high metabolic demands. Finally, the central nervous system has its own, dedicated immune protection, provided by microglia, to deal with injury and infection. Failure of any of these protective mechanisms can lead to permanent brain damage and associated functional deficits. Acquired brain damage as a result of a stroke is unfortunately a common issue. Strokes represent the third-leading cause of death, but equally significant is the fact that they are the leading cause of adult disability. Deficits that impact on motor function can have direct effects on the ability of sufferers to perform basic oral hygiene practices.
Neurodegenerative disorders, such as Alzheimer’s disease and Parkinson’s disease, also represent a growing concern, particularly with our aging populations. While, as with cancer, increasing age is a risk factor for their development, it is not, in itself, a cause. Although there is still much to learn about the pathological mechanisms underlying neurodegenerative disorders, the mis-folding of proteins during their synthesis, and the subsequent aggregation of insoluble proteins, does appear to be an important, common mechanism. However, there is also evidence that inflammation, and particularly chronic neuroinflammation, also plays a role in neurodegenerative processes.
The disorders, Huntingdon’s disease, motor neurone disease and multiple sclerosis will also be considered in turn.
In relation to oral health, much of the impact of these disorders is due to their effect on oral hygiene practices, although there may also be issues around medication, and patient management in the dental clinic. Dental professionals may also need to work collaboratively with these patients’ carers in order to achieve the best oral-health outcomes.
A stroke, or cerebrovascular accident, is associated with an interruption of the blood supply to a region of the brain that results in an infarction, or neuronal death, in the affected area. Normal cerebral perfusion can be interrupted in a number of different ways. The most common mechanism is a thrombotic event within a cerebral artery. Thrombotic strokes are frequently associated with the development of an atherosclerotic plaque in a cerebral artery. The plaque causes narrowing, and eventual occlusion of a vessel due to thrombus formation, particularly if the plaque ruptures. Strokes may also occur as a result of an embolism. Embolic strokes commonly involve blood clot, or thrombus, fragments that have formed outside of the brain, and travel to the brain through the circulation. Once in the cerebral circulation, they may occlude a cerebral vessel, commonly at a site of vessel bifurcation or narrowing. By their nature, the onset of embolic strokes is always very sudden and can involve very large regions of brain. Predisposing factors for embolic strokes include atrial fibrillation, bacterial endocarditis, and heart valve disease. Together, thrombotic and embolic strokes are referred to as ischaemic strokes, and account for more than 80% of all cerebrovascular accidents.
Other cerebrovascular accidents are associated with haemorrhage. Haemorrhagic strokes, also known as intracerebral haemorrhages, are most commonly caused by uncontrolled hypertension leading to weakening, and subsequent rupture of a blood vessel. Haemorrhagic strokes most commonly occur in deeper brain structures, particularly in the region of the basal ganglia.
A very severe headache is a consistent finding, while other symptoms depend upon the region affected. The release of blood from the ruptured vessel can cause further ischaemia in the brain, as a result of cerebral vasospasm.
A subarachnoid haemorrhage, where there is bleeding in the subarachnoid space of the meningeal membranes, can also cause a stroke. The rupture of a vessel is most commonly associated with the presence of an aneurysm, which weakens the vessel wall, although subarachnoid haemorrhages may also occur with head injuries. The risk of an aneurysm rupturing is exacerbated by uncontrolled hypertension.
The mechanisms associated with ischaemic strokes can also give rise to transient ischaemic attacks (TIAs). In some cases, the obstructing clot can be efficiently removed by the body’s fibrinolytic system before any permanent tissue damage occurs. As a result, the early symptoms of the ‘stroke’ can resolve without evidence of neurologic dysfunction. However, these signs should not be ignored, since TIAs are an important warning sign of cerebrovascular disease, and sufferers carry a high risk of a subsequent stroke.
The signs and symptoms of a stroke will vary depending upon the vessel, and with that, the area of the brain affected. The initial signs of a stroke normally comprise a mixture of motor and sensory impairment. Motor impairment may result in weakness or clumsiness on one side of the body, along with difficulties in swallowing, slurred speech, and double vision. There may also be problems with language comprehension, balance and vision, as well as somatosensory loss.
It is important to be aware of the signs of a stroke, since early clinical intervention is critical. The acronym FAST (Facial weakness; Arm weakness; Speech problems; Time to call) has been proposed as an easy mechanism for assessment. Early detection and intervention with a stroke is critical, although therapeutic management is limited. Early identification of an ischaemic stroke can allow for the administration of the tissue plasminogen activator (tPA), alteplase, to remove the clot. However, most therapeutic intervention for stroke is aimed at prevention.
Since the majority of strokes are triggered by either a blood clot, or clot fragment, prevention of thrombus formation is a cornerstone of prevention. Depending on stroke risk, patients may either be prescribed antiplatelet (e.g. aspirin, clopidogrel) or anticoagulant (e.g. warfarin, dabigatrin) medication. Obviously, the potential for excessive bleeding needs to be managed within the dental clinic. However, this must be achieved by the use of local measures rather than the cessation of anticoagulant or antiplatelet therapy.