Disorders of the nervous system

Chapter 8
Disorders of the nervous system


Petra Brown


Aim


The aim of this chapter is to provide the reader with an overview of the nervous system, and an understanding of the pathophysiological changes that are associated with disorders of this system.



Introduction


In conjunction with the endocrine system, the nervous system interacts with all body systems to maintain homeostasis. It is a complex system which co‐ordinates and controls voluntary and involuntary action. It orientates us to the internal and external environment through sensory mechanisms. The nervous system assimilates experiences and information through memory, intelligence, learning and dreaming. It provides us with instinctual information and reflexes, at birth and beyond.


Structure of the nervous system


While the nervous system functions as a whole, it is useful to subdivide its anatomical structure and physiological components (Table 8.1, Fig. 8.1), to assist in understanding its complexity.


Table 8.1 Anatomical structure of the nervous system










Central nervous system (CNS) Peripheral nervous system (PNS)


  • Brain
  • Spinal cord


  • Cranial nerves
  • Spinal nerves
  • Sensory (afferent) neurones
  • Motor (efferent) neurones
  • Somatic nervous system (voluntary)
  • Autonomic nervous system (involuntary)

    • sympathetic
    • parasympathetic
Flow diagram of organisation of the nervous system with boxes connected by arrows labeled Central nervous system (CNS) Brain and spinal cord, Somatic nervous system Voluntary control, etc.

Figure 8.1 Organisation of the nervous system.


Central and peripheral nervous system


The nervous system may be divided into the central nervous system (CNS) and peripheral nervous system (PNS).


Physiologically, the nervous system is subdivided and organised as shown in Fig. 8.1.


Cellular structure of the nervous system


Highly specialised neurone (nerve) and neuroglia (nerve fibre) cells provide the cellular building blocks of the nervous system. Neurones are nerve cells primarily involved with the transmission of information, while neuroglial cells provide a variety of supportive functions.


Transmission of nerve impulses


There are three types of nerve impulse transmission in the nervous system. Simple linear transmission passes electrical action potentials along neurones, through the exchange of sodium and potassium across cell membranes. This causes polarisation and depolarisation along the neurone. Saltatory conduction passes electrical action potentials along myelinated neurones. The action potential jumps between the nodes of Ranvier, thus travelling much faster than by simple linear transmission. The third type of transmission occurs via chemical neurotransmitters at synaptic endings. These include acetylcholine in the CNS and at neuromuscular junctions. Dopamine and norepinephrine (noradrenaline) are found within the CNS and autonomic nervous system. Other common synaptic neurotransmitters include serotonin and GABA (gamma‐aminobutyric acid).


Disorders of the nervous system


Introduction


This section will outline some of the common neurological disorders encountered in childhood. The term applies to any condition that is caused by a dysfunction in the brain or nervous system, resulting in physical, behavioural and cognitive symptoms. The nervous system is a highly complex and integrated system and disorders are categorised by their causative nature. These include neurological dysfunction, cerebral dysfunction, head and spinal trauma, motor dysfunction, neurological tumours, infection and seizures.


Causes of neurological dysfunction


Prenatal causes


These occur in the womb during pregnancy. To recap, the nervous system develops early in the third week of embryonic development to form a neural tube, in a process called neurulation. During the fourth and eleventh week, distinct areas of the brain are formed. The peripheral nervous system develops from the neural crest at around 4 weeks, alongside the spinal, cranial and autonomic nervous system. Growth continues until at birth, all the major structures of the nervous system are present. Exposure to factors, which may hinder neural development in pregnancy, may cause intellectual, behavioural and developmental problems.



  • Neurotoxins can enter and damage a fetus’s nervous system, via the placenta leading to neurological problems as the child develops. Fetal alcohol syndrome is linked to alcohol ingestion during pregnancy. Tobacco ingestion has been linked to challenging behaviours and developmental impairment. Lead and mercury ingestion have been linked to intelligence, memory, learning and development problems.
  • Nutritional deficiencies in the last 3 months of pregnancy can decrease the number of brain cells. Spina bifida is linked to a maternal deficiency of folic acid before or during the early stages of pregnancy.
  • Infections can be transmitted across the placenta from the mother. They can cause developmental problems and cerebral palsy in the case of chorioamnionitis. The Zika virus causes microcephaly, wherein the baby’s head is smaller than normal and the brain may not be fully developed. Other infections, which cause prenatal dysfunction, include toxoplasmosis, rubella, cytomegalovirus, HIV, herpes simplex, hepatitis B and syphilis.
  • Birth complications such as hypoxic brain damage can occur if the umbilical cord blood supply is interrupted or compromised during birth. The resultant lack of oxygen and nutrients can cause brain damage.

Congenital causes


Genetic abnormalities can lead to a variety of neurological disorders. In the main, genetic disorders are inherited rather than mutations of normal DNA. Inheritance is through an equal combination of parental chromosomes that create the fetal DNA. Human cells have 22 pairs of autosomes and 1 pair of sex chromosomes making a total of 46 chromosomes. This DNA contains the ‘code’, which makes us who we are and a number of factors can interact, in complex ways, to cause neurological and other disorders.



  • Genetic mutations cause abnormalities that lead to alteration in development and can therefore cause neurological damage. Phenylketonuria is such an example, where the child inherits a faulty gene from each parent.
  • Chromosome disorders have widespread effects because each chromosome contains approximately 20 000 genes. Down syndrome is caused by the presence of an extra copy of chromosome 21. Turner syndrome is caused by the loss of a chromosome. Microdeletions and microduplications of gene fragments can lead to conditions such as Cri‐du‐chat, 5p− and Prader‐Willi syndromes.
  • Metabolic disorders can cause neurological damage and need to be detected early. Babies with the inherited condition phenylketonuria (PKU) are unable to metabolise phenylalanine, which is present in food. High blood concentrations cause brain cell damage and affect intellectual ability. Many countries now routinely test babies at birth for the presence of phenylketonuria.

Acquired causes


These develop after birth and may be caused by trauma, infection, exposure to toxins, autoimmune disorders, epilepsy and neurological tumours.


Cerebral dysfunction


Cerebral dysfunction may be focal or global and alters the function of the brain and cerebral processes. Focal or localised dysfunction is caused by structural abnormalities such as tumours, local haemorrhage, congenital and acquired malformations. Global cerebral dysfunction affects the whole brain and is caused by metabolic, hypoxic, toxic, infective, haemorrhagic or traumatic events


Pathophysiology of raised intracranial pressure (ICP)


There are four interconnected cerebral ventricles in the brain. They are filled with cerebrospinal fluid (CSF) which continuously circulates through the ventricles and in the subarachnoid space around the brain and spinal cord.


ICP is one of the main sequela of cerebral dysfunction (Fig. 8.2). It may be caused by an increase in the volume within the cranium such as tumour growth, oedema, inflammation (meningitis), developmental abnormalities, excessive cerebrospinal fluid (hydrocephalus) or bleeding (haemorrhage).

Cycle diagram of raised ICP, from brain injury to raised ICP, to reduced cerebral blood flow, to brain tissue hypoxia, to increased oedema formation, and back to raised ICP. A pair of clockwise arrows are at the center.

Figure 8.2 Raised intracranial pressure (ICP).


The CSF has four main functions, which include mechanical protection of the delicate brain tissue against sudden contact with the hard bones of the skull. CSF supports the mass of the brain, preventing ischaemia in the lower parts. Chemical protection against fluctuations in pH and ionic composition and circulation of oxygen, nutrients and removal of waste products from cerebral metabolic processes, such as carbon dioxide.


Abnormal changes in ICP will influence cerebral blood flow. A raised ICP will lead to reduced blood flow, preventing adequate delivery of oxygen (O2) and nutrients such as glucose to the brain cells. This lack of oxygen rapidly leads to brain tissue hypoxia. Concurrently carbon dioxide (CO2) removal is impaired by a reduced blood flow and its accumulation will result in acidosis and a fall in pH.


Autoregulation and chemoregulation become impaired, leading to vasodilation of the cerebral blood vessels. This is initially the brain’s attempt to increase blood, O2 and nutrient flow to cerebral cells. In the confined space of the skull, there is nowhere for this increase in blood volume to go, causing fluid to ‘leak’ out of the cerebral arteries. This oedema formation leads to a further increase in ICP, causing blood flow to become more impaired. The brain is extremely sensitive and a lack of oxygen for more than 3 minutes will result in cerebral cell death.


As the ICP rises, CSF is prevented from draining from the ventricles into the subarachnoid space, leading to a further increase in ICP. If this pressure persists, the fluid build‐up compresses and damages brain tissue. Raised ICP ultimately causes herniation of brain tissue through the foramen magnum at the base of the skull. This compression and herniation of the brain stem, through the space where the spinal cord enters, is also referred to as coning and inevitably results in death.


Initially, clinical signs of raised ICP include:



  • decreasing levels of consciousness
  • headache that increases in intensity with coughing and straining
  • slow pupil constriction when exposed to bright light
  • visual disturbances such as blurred vision due to papilloedema, which is swelling of the optic disc
  • convulsion and seizure activity
  • abnormal breathing patterns
  • impaired motor or sensory function and responses
  • speech and swallowing difficulties
  • altered mood and challenging behaviour.


In later stages, if condition worsens and ICP continues to rise:



  • decerebrate or decorticate posturing
  • bulging anterior fontanelle (babies only)
  • head enlargement when cranial sutures have not fused (babies only)
  • vomiting
  • high temperature without a clear indication of infection
  • Cushing’s reflex, also known as the vasopressor response, will result in the clinical signs known as Cushing’s triad:

    • raised systolic blood pressure with widening pulse pressures
    • bradycardia, reduction in the heart rate
    • irregular, shallow or slow respirations.

Treatment of a raised ICP will vary depending on the causative condition. The overall aim is to decrease ICP and this may be achieved in several ways, such as reducing the cerebral volume caused by a tumour or inflammation. Draining excess CSF and decreasing the cerebral blood volume, will reduce a raised ICP. Lowering the brain’s metabolic rate will reduce cerebral demand of oxygen and nutrients and can be achieved through administration of prescribed sedation, anti‐emetics and pharmacological seizure management.


Hydrocephalus


Hydrocephalus causes global cerebral dysfunction, due to increased levels of cerebrospinal fluid (CSF) in the brain and spinal cord. It can be congenital or acquired after birth.


Congenital hydrocephalus is present at birth and can be caused by conditions such as spina bifida, inflammation or tumours. Maternal infections during pregnancy such as mumps or rubella can also be a cause.


Acquired hydrocephalus occurs after birth and usually develops after an injury, illness or development of a brain tumour.


In both, the CSF volume increases, leading to an increase in intracranial pressure (ICP). If this increased pressure persists, the fluid build‐up compresses and damages brain tissue. Specific clinical signs of hydrocephalus are caused by the increasing CSF volume and pressure inside the cranium that result in:



  • head enlargement in babies and children with congenital hydrocephalus
  • bulging anterior fontanelle (babies only)
  • dilated scalp veins and separation of skull sutures (later sign)
  • downward eye gaze (also known as the ‘setting‐sun’ sign)
  • convulsions
  • other signs of raised ICP.

Hydrocephalus is an acute life‐threatening emergency, which must be treated promptly. Early diagnosis is critical in the older child, whose skull bones have fused, leaving little room for swelling and which will rapidly lead to raised ICP.


Treatment involves implanting a thin tube, called a shunt, in the brain. The excess CSF in the brain runs through the shunt to another part of the body, usually the peritoneal cavity. From here, the CSF is absorbed into the blood stream. The shunt has a valve inside it to control the flow of CSF and to ensure it does not drain too quickly (Corns & Martin, 2012).


Cerebral trauma


Fractured skull


Skull fractures can be linear, depressed or open. Linear fractures show no signs of skull depression and are treated conservatively. Depressed skull fractures with a depression of more than 1 cm and open skull fractures may need surgical intervention and repair of the damaged structure. Evidence of a meningeal tear, CSF leakage, cranial nerve damage, seizure activity or a risk of infection make this more likely.


Table 8.2 illustrates specific signs and symptoms that may be present in a child with a fractured skull.


Table 8.2 Vital signs and symptoms of a fractured skull


Source: Glasper et al., 2011.





Symptoms can include:

  • Bruising around the eyes (‘panda/raccoon eyes’), which is caused by a basal skull fracture. A rupture of the meninges causes blood to pool in the peri‐orbital area via the cranial sinuses.
  • Bruising over the mastoid bone (‘Battle’s sign’), behind the ear, is usually caused by a fracture of the posterior cranial fossa. This is a later sign and often does not appear for 24 hours post injury.
  • Blood in the ear canal.
  • Cerebrospinal fluid (CSF) leakage from the nose or ears, due to a basal skull fracture.
  • A palpable dent or spongy area of the head, indicating a depressed skull fracture.

Signs depend on the area of injury and can include:

  • Evidence of raised ICP.
  • Visual disturbance, due to optical nerve compression/damage or rising ICP.
  • Facial muscle weakness, altered facial sensation and loss of smell due to cranial nerve damage.
  • Speech impairment.
  • Loss of hearing due to inner ear haemorrhage or ruptured eardrum.
  • Dizziness, vertigo and other balance problems.
  • Impaired motor or sensory function and responses.

Consider a C‐spine injury in all head injuries.

Urgent assessment using an ABCDE approach and a full neurological assessment, including Paediatric Early Warning System (PEWS), AVPU (alert, voice, pain, unresponsive) and Glasgow Coma Scale (GCS), is imperative to assess the level of consciousness and awareness (Table 8.3).


Table 8.3 Investigations to assess level of consciousness


Source: Glasgow Coma Scale 2014.







  1. The AVPU response scale can be used quickly to assess the level of consciousness. A score lower than V is a cause for concern and requires urgent medical referral
    A the patient is awake
    V the patient responds to verbal stimulation
    P the patient responds to painful stimulation
    U the patient is completely unresponsive.

  2. The Glasgow Coma Scale (GCS) is used to provide a practical method for the assessment of conscious level in response to defined stimuli. The GCS can be used without modification for children over 5 years old. Under 5 years old, it will be difficult for children to ‘obey commands’ or give a verbal response that indicates that they are ‘orientated’. Thus, the Paediatric Glasgow Coma Scale (PGCS) may be more appropriate. (Amended PGCS stimuli are shown below in brackets.)
GCS stimuli include:


  • Eye opening

    • 4. Eyes opening spontaneously
    • 3. Eye opening to speech
    • 2. Eye opening to pressure
    • 1. No eye opening or response

  • Verbal response

    • 5. Orientated (smiles, oriented to sounds, follows objects, interacts)
    • 4. Confused (cries but consolable, inappropriate interactions)
    • 3. Words (inconsistently inconsolable, moaning)
    • 2. Sounds (inconsolable, agitated)
    • 1. No verbal response

  • Motor response

    • 6. Obeys commands (infant moves spontaneously or purposefully)
    • 5. Localises (infant withdraws from touch)
    • 4. Normal flexion (infant withdraws from pressure)
    • 3. Abnormal flexion to pain (decorticate response)
    • 2. Extension to pain (decerebrate response)
    • 1. No motor response
Each response has a value and these should be considered individually and as a combined score. A combined score of less than eight represents a significant risk of mortality. The GCS should be recorded regularly on a GCS chart. This will allow the nurse to observe trends that can indicate improvement or deterioration of the patient’s condition.

Emergency nursing care includes assisting with intubation and ventilation if the airway and breathing are compromised by damage to the respiratory centre in the brain. Immobilise the cervical spine if a fracture is suspected. Continuously monitor vital signs for indications of rising ICP, using the GCS and PEWS chart (Table 8.3). A full neurological assessment should include level of consciousness, cranial nerves, motor and sensory function and cerebellar function. Assess for other injuries and open wounds, including a fractured skull. Only treat/suture if this will not delay further investigations/transfers. Assess pain levels, using an age‐appropriate pain tool and administer analgesia. Administer an anti‐emetic as prescribed because vomiting can raise ICP further. Assess the efficacy of analgesia and anti‐emetic. Ensure family‐centred care is implemented, through effective communication and liaison with the child, family and carers. Offer reassurance and support if the child needs to be prepared for transfer to an intensive care or neurological unit (Glasper, McEwing & Richardson, 2011).


Head injury


This occurs when trauma to the head results in damage to the brain. There are three main types of traumatic brain injury (TBI).



  • Closed head injuries – where no damage is visible. These are common in car accidents where the moving head suddenly stops or the child experiences a blow to the head.
  • Open wounds – such as occur in conjunction with a fractured skull. The brain is exposed and may have been damaged by an object or a blow to the head.
  • Crushing injuries– where the head is crushed and brain damage occurs.

Brain injuries may be classified as either focal or diffuse (see Fig. 8.3). Focal injuries are localised to one area, whereas diffuse injuries occur throughout the brain and CNS.

A box labeled Focal has arrows pointing to contusion, laceration, and haemorrhage (top) and another labeled Diffuse has arrows pointing to concussion, acute axonal injury, and hypoxic injury (bottom).

Figure 8.3 Focal and diffuse brain injury types.


Focal head injuries include contusions, lacerations and haemorrhage


Contusions or bruising, occur as the brain comes into contact with the hard inner skull. The most common areas of injury are the frontal and temporal lobes. The cerebral trauma results in the leakage of blood from microscopic vessels and the possibility of a tear in the delicate meninges, causing a haemorrhage.


Lacerations are tears in the brain tissue. A fractured skull or the entrance of a foreign object, such as a bullet into the skull, usually causes a laceration. This will result in the rupture of large blood vessels causing bleeding into the brain leading to haemorrhage, haematoma formation, cerebral oedema and raised ICP.


Haemorrhage occurs when large or small blood vessels are damaged causing bleeding into the brain. Blood is supplied to the brain from the aorta via the internal carotid and vertebral arteries. Venous blood returns to the heart via the jugular veins and superior vena cava. The brain is very susceptible to interruption in blood supply, which leads to rapid O2 and glucose deprivation of the delicate neural tissues.


A haemorrhage is classified according to the space it occurs in (Fig. 8.4).



  • Intracerebral haemorrhage occurs deep within the brain tissue.
  • Subdural haemorrhage occurs in the subdural space between the dura mater and arachnoid mater. It commonly occurs in abusive head trauma or shaken baby syndrome, although other symptoms would also need to be taken into consideration to make a full diagnosis (New Scientist, 2016).
  • Subarachnoid haemorrhage occurs in the subarachnoid space between the arachnoid mater and pia mater. It can result from a tear in the pia mater allowing blood to enter the subarachnoid space. It can also result from the rupture of aneurysms or arteriovenous malformations, often present in the circle of Willis. The circle of Willis connects cerebral arteries, allowing for rapid redistribution of arterial blood to be diverted to dependant areas of the brain.
Anterior view of frontal section through the skull displaying the cranial meninges including Dura mater, Arachnoid mater, and Pia mater with other parts labeled Cerebral cortex, Parietal bone of cranium, etc.

Figure 8.4 Anterior view of frontal section through the skull showing the cranial meninges.


Source: Tortora & Nielsen 2009.


Diffuse head injuries include concussion, acute axonal and hypoxic injury. Concussion is usually a mild diffuse injury and is the most common brain injury. It may cause temporary loss of consciousness (lasting minutes to hours), confusion, amnesia, visual disturbances, vestibular imbalance, headaches and nausea and vomiting.


Axonal injury is usually caused by high‐speed acceleration/deceleration injuries. It causes diffuse haemorrhages throughout the brain and may cause the patient to become deeply unconscious.


Hypoxic injury is caused by oxygen deprivation such as a cardiac arrest or near drowning and may not be associated with a head injury. However, it must be noted that hypoxic injury may compound the effects of a brain injury.

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Mar 27, 2019 | Posted by in NURSING | Comments Off on Disorders of the nervous system

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