Central nervous system 3 – genetic and developmental disorders

Central nervous system 3 – genetic and developmental disorders

Alan Nimmo

Key Topics

  • Introduction to psychiatric and neurological disorders
  • Seizures and epilepsy
  • Schizophrenia
  • Cerebral Palsy
  • Down syndrome

Learning Objectives

  • Be aware of the distinction between seizures and epilepsy
  • Be aware of the impact epilepsy, and its management, may have upon oral health and, should the need arise, how to manage seizures in the dental clinic
  • Be aware of the impact that conditions such as schizophrenia may have upon oral health, and the importance of good preventive care
  • Be aware of the impact of cerebral palsy upon oral health, the importance of preventive care, and the careful management of patients in the dental clinic

Introduction

Psychiatric and neurological disorders are very common in society, but they are often poorly understood. Unfortunately, individuals with these conditions are more susceptible to systemic disease, and are likely to have poorer oral health than other members of the general population. Individuals with severe mental illness are more likely to have decayed, missing or filled teeth. These individuals should have the same level of access to quality healthcare as all members of society. In order to help bridge this gap, it is important to have an understanding of the common neurological conditions, and the approaches that are taken to help manage these conditions. In this way, we can try to prevent these conditions from becoming a barrier to good general and oral healthcare, and develop strategies for improving oral health.

The central nervous system is the most complex organ system within the human body, and we are only beginning to understand its function, and the conditions that affect it. There are some CNS disorders, such as Huntington’s disease (Chapter 12), that are linked to a single gene. Other CNS disorders may have a genetic component that serves as a predisposition to developing a particular condition. Whether one does or not, may depend upon other influences, such as environmental factors. For example, with epilepsy, we all have a certain seizure threshold in our brain (i.e. a tendency to develop seizure activity). Individuals with a low seizure threshold, which appears to have a genetic component, are more predisposed to developing epilepsy than others. However, even identical, or monozygotic, twins, who share identical genetic material, will not necessarily both develop epilepsy. Environmental factors, such as injury or inflammation, may serve as the actual trigger for the development of epilepsy. Other conditions, such as cerebral palsy, may be acquired during brain development. Injury to the brain may occur as the result of insults like infection or hypoxia that occur anytime from in utero development through to the early childhood years.

There may be a number of factors that can impact upon oral health. Patients may have poor oral hygiene as a result of neglect, lack of motivation, or reduced physical ability to perform good oral care. A patient’s medication may also impact upon their oral health, with xerostomia being a common issue. Patients may have problems accessing healthcare facilities, and may require additional support and understanding within the dental clinic. Where appropriate, dental professionals may also need to work collaboratively with a patient’s carers in order to achieve the best oral-health outcomes.

Seizures and epilepsy

The term seizure applies to the situation where there is an episode of abnormal electrical activity within the brain, which will disrupt normal neuronal activity, and as such, normal brain function. The precise impact of a seizure will depend upon where the abnormal activity occurs, and how widespread the disruption is. The site at which the abnormal activity begins is regularly referred to as the focus, but it may subsequently spread to other areas of the brain. While seizures are commonly thought to involve physical convulsions of the sufferer, that is not always the case. Certainly, if the motor cortex is involved, then convulsions will be observed. However, as with strokes, the precise signs and symptoms depend upon the specific area that is affected. For example, if the seizure involves the brain stem, and in particular the reticular formation, then a loss of consciousness may be observed.

Seizures themselves represent a symptom of some underlying neurological disorder. They are thought to occur as a result of altered neuronal excitability, which may occur through changes at the level of the neuronal cell membrane, or an imbalance between normal excitatory (e.g. glutamate) and inhibitory (e.g. γ-aminobutyric acid (GABA)) transmission in the brain. Seizures may be classified as either being provoked or unprovoked. With provoked seizures, the abnormal activity can be clearly linked to some direct underlying cause. For example, seizures may be triggered by a high fever, particularly in children (febrile seizures), or due to hypoxia or hypoglycaemia. These provoked seizures are best dealt with by treating the underlying cause, for example the use of anti-pyretic medication for febrile seizures. With unprovoked seizures, no obvious underlying cause is observed. This type of seizure is primarily associated with the condition of epilepsy.

Epilepsy is the term used to describe conditions where there is an associated risk of repeated episodes of seizure activity. It is a relatively common disorder, affecting between 0.5% and 1% of the population. There is strong evidence for a genetic component to the condition, and a number of genes, particularly ones encoding for neuronal ion channels and neurotransmitter receptors, have been implicated in the development of the condition. However, while heritability is high, environmental factors also have an influence, since just over half of identical twins will both develop the condition.

Both seizures and epileptic seizures are classified according to the location, nature and impact of the seizure activity. The first distinction is to categorize a seizure as being focal or generalized. Focal seizures describe the situation where the abnormal activity, at least to begin with, is relatively localized. Previously, these were more commonly referred to as partial seizures. In some cases a specific brain lesion may be identified as being responsible for the epileptic focus. The precise impact of that seizure will depend upon the region of the brain that is affected. For example if the motor cortex is involved convulsions will be observed.

A generalized seizure refers to the situation where the seizure activity spreads rapidly to involve multiple areas of the brain, including cortical and subcortical structures. Generalized seizures are grouped into a number of classes, with two important groups being tonic-clonic seizures and absence seizures. From a clinical perspective, a tonic-clonic seizure can represent a confronting situation for the clinician. The seizure begins with whole-body muscle spasms that last about a minute, and cause breathing to stop. The patient’s face will become blue, unlike a fainting episode, where it normally becomes pale. This is followed by a few minutes of jerking contractions, which gradually phase out. The patient is likely to remain unconscious for a few more minutes, before slowly recovering. When the patient comes round, they are likely to be confused, feel unwell, and require reassurance. Occasionally a patient may experience a series of unremitting seizures, and this situation, referred to as status epilepticus, constitutes a medical emergency (see Chapter 10

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Aug 15, 2017 | Posted by in Orthodontics | Comments Off on Central nervous system 3 – genetic and developmental disorders
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