Epidemiology

There are problems in establishing precise epidemiological information for a heterogeneous condition such as epilepsy. Unlike most ailments, epilepsy is episodic; between seizures, patients may be perfectly normal and have normal investigations. Thus, the diagnosis is essentially clinical, relying heavily on eyewitness descriptions of the attacks. In addition, there are a number of other conditions in which consciousness may be transiently impaired and which may be confused with epilepsy. Another problem area is that of case identification. Sometimes the person may be unaware of the nature of the attacks and so may not seek medical help. People with milder epilepsy may also not be receiving ongoing medical care and so may be missed in epidemiological surveys. Furthermore, since there is some degree of stigma attached to epilepsy, people may sometimes be reluctant to admit their condition. Indeed, epilepsy is still one of the world’s most stigmatised conditions. In today’s society, in both developed and developing countries, fear, misunderstanding, discrimination and social stigma still exist and these affect the quality of life for people with the disorder and their families.

Epilepsy does impact on an individual’s human rights, for example, access to health and life insurance is affected. A person who suffers from epilepsy may not be able to obtain a driving licence and it has an impact on the choice of career. In addition, legislation can impact on the life of individuals with epilepsy, for example, in some countries epilepsy may deter marriages. Legislation based on internationally accepted human rights standards can prevent discrimination and rights violations, improve access to health care services and raise quality of life (WHO, 2009). A global campaign has been established to raise awareness about epilepsy, provide information and highlight the need to improve care and reduce the disorder’s impact through public and private collaboration. This is supported through a partnership established between WHO, the International League Against Epilepsy (ILAE) and the International Bureau for Epilepsy (IBE).

Epilepsy is recognised as a priority in effective health care delivery and there are still a number of issues that health professionals should consider:

Aetiology

Epileptic seizures are produced by abnormal discharges of neurones that may be caused by any pathological process which affects the cortical layer of the brain. The idiopathic epilepsies are those in which there is a clear genetic component, and they probably account for a third of all new cases of epilepsy. In a significant proportion of cases, however, no cause can be determined and these are known as the cryptogenic epilepsies. Possible explanations for cryptogenic epilepsy include as yet unexplained metabolic or biochemical abnormalities and microscopic lesions in the brain resulting from brain malformation or trauma during birth or other injury. The term ‘symptomatic epilepsy’ indicates that a probable cause has been identified.

The likely aetiology of epilepsy depends upon the age of the patient and the type of seizure. The commonest causes in young infants are hypoxia or birth asphyxia, intracranial trauma during birth, metabolic disturbances and congenital malformations of the brain or infection. In young children and adolescents, idiopathic seizures account for the majority of the epilepsies, although trauma and infection also play a role. In this age group, particularly in children aged between 6 months and 5 years, seizures may occur in association with febrile illness. These are usually short, generalised tonic clonic convulsions that occur during the early phase of a febrile disease. They must be distinguished from seizures that are triggered by central nervous system infections which produce fever, for example, meningitis or encephalitis. Unless febrile seizures are prolonged, focal, recurrent or there is a back-ground of neurological handicap, the prognosis is excellent and it is unlikely that the child will develop epilepsy.

The range of causes of adult-onset epilepsy is very wide. Both idiopathic epilepsy and epilepsy due to birth trauma may also begin in early adulthood. Other important causes are head injury, alcohol abuse, cortical dysplasias, brain tumours and cerebrovascular diseases. Brain tumours are responsible for the development of epilepsy in up to a third of patients between the ages of 30 and 50 years. Over the age of 50 years, cerebrovascular disease is the commonest cause of epilepsy, and may be present in up to half of patients.

Pathophysiology

Epilepsy differs from most neurological conditions as it has no pathognomonic lesion. A variety of different electrical or chemical stimuli can easily give rise to a seizure in any normal brain. The hallmark of epilepsy is a rather rhythmic and repetitive hyper-synchronous discharge of neurones, either localised in an area of the cerebral cortex or generalised throughout the cortex, which can be observed on an electroencephalogram (EEG).

Neurones are interconnected in a complex network in which each individual neurone is linked through synapses with hundreds of others. A small electrical current is discharged by neurones to release neurotransmitters at synaptic levels to permit communication with each other. Neurotransmitters fall into two basic categories: inhibitory or excitatory. Therefore, a neurone discharging can either excite or inhibit neurones connected to it. An excited neurone will activate the next neurone whereas an inhibited neurone will not. In this manner, information is conveyed, transmitted and processed throughout the central nervous system.

A normal neurone discharges repetitively at a low baseline frequency, and it is the integrated electrical activity generated by the neurones of the superficial layers of the cortex that is recorded in a normal EEG. If neurones are damaged, injured or suffer a chemical or metabolic insult, a change in the discharge pattern may develop. In the case of epilepsy, regular low-frequency discharges are replaced by bursts of high-frequency discharges usually followed by periods of inactivity. A single neurone discharging in an abnormal manner usually has no clinical significance. It is only when a whole population of neurones discharge synchronously in an abnormal way that an epileptic seizure may be triggered. This abnormal discharge may remain localised or it may spread to adjacent areas, recruiting more neurones as it expands. It may also generalise throughout the brain via cortical and subcortical routes, including collosal and thalamocortical pathways. The area from which the abnormal discharge originates is known as the epileptic focus. An EEG recording carried out during one of these abnormal discharges may show a variety of atypical signs, depending on which area of the brain is involved, its progression and how the discharging areas project to the superficial cortex.

Clinical manifestations

The clinical manifestation of a seizure will depend on the location of the focus and the pathways involved in its spread. An international seizure classification scheme based on the clinical features of seizures combined with EEG data is widely used to describe seizures. It divides seizures into two main groups according to the area of the brain in which the abnormal discharge originates. If it involves initial activation of both hemispheres of the brain simultaneously, the seizures are termed ‘generalised’. If a discharge starts in a localised area of the brain, the seizure is termed ‘partial’ or ‘focal’.

Diagnosis

Diagnosing epilepsy can be difficult as it is first necessary to demonstrate a tendency to recurrent epileptic seizures. The one feature that distinguishes epilepsy from all other conditions is its unpredictability and transient nature. The diagnosis of epilepsy is clinical and depends on a reliable account of what happened during the attacks, if possible both from the patient and from an eyewitness. Investigations may help and the EEG is usually one of them. These investigations, however, cannot conclusively confirm or refute the diagnosis of epilepsy.

There are other conditions that may cause impairment or loss of consciousness and which can be misdiagnosed as epilepsy; these include syncope, breath-holding attacks, transient ischaemic attacks, psychogenic attacks, etc. In addition, people may present with acute symptomatic seizures or provoked seizures as a result of other problems such as drug intake, metabolic dysfunction, infection, head trauma or flashing lights (photosensitive seizures). These conditions have to be clearly ruled out before a diagnosis of epilepsy is made. Epilepsy must only be diagnosed when seizures occur spontaneously and are recurrent. The diagnosis must be accurate since the label ‘suffering with epilepsy’ carries a social stigma that has tremendous implications for the person.

The EEG is often the only examination required, particularly in generalised epilepsies, and it aims to record abnormal neuronal discharges. EEGs have, however, limitations that should be clearly understood. Up to 5% of people without epilepsy may have non-specific abnormalities in their EEG recording, while up to 40% of people with epilepsy may have a normal EEG recording between seizures. Therefore, the diagnosis of epilepsy should be strongly supported by a bona fide history of epileptic attacks. Nevertheless, the EEG is invaluable in classifying seizures.

The chance of recording the discharges of an actual seizure during a routine EEG, which usually takes 20–30 min, is slight and because of this, ambulatory EEG monitoring and EEG video-telemetry are sometimes required. Ambulatory EEG allows recording in day-to-day circumstances using a small cassette recorder. EEG video-telemetry is useful in the assessment of difficult cases, particularly if surgery is considered. The person is usually admitted to hospital and remains under continuous monitoring. This is only helpful in a very few cases, and it is best suited for people who have frequent seizures.

Neuroimaging with magnetic resonance imaging (MRI) is the most valuable investigation when structural abnormalities such as stroke, tumour, congenital abnormalities or hydrochephalus are suspected. MRI should be carried out in anyone presenting with partial seizures or where a structural lesion on the brain may be responsible for seizures.

Treatment

National Institute for Health and Clinical Excellence (2004a) issued guidance on the diagnosis and treatment of the epilepsies in adults and children in primary and secondary care. The guidance covered issues such as when a person with epilepsy should be referred to a specialist centre, the special considerations concerning the care and treatment of women with epilepsy and the management of people with learning disabilities. The key points of the guidance are summarised in Box 31.1.