WHO Fact Sheet No 165 June 1997

EPILEPSY: AETIOLOGY, EPIDEMIOLOGY AND PROGNOSIS

Epilepsy is a universally occurring disorder and one of the oldest known to mankind. It is characterized by a tendency to recurrent seizures which can lead to loss of awareness or consciousness, disturbances of movement, sensation (including vision, hearing and taste), autonomic function, mood and mental function.

It was, and still is, widely believed that a person with epilepsy is seized by a supernatural force or power. This ancient belief is reflected in the name of the disorder -- the word "epilepsy" is derived from the Greek word "epilepsia", which means "to take hold of" or "to seize".

It is, however, now known that seizures are the result of sudden, usually brief, excessive electrical discharges in a group of brain cells (neurones). Different parts of the brain can be the site of such an electrical discharge. The clinical manifestations of seizures are, therefore, variable and depend on the site and the function of the brain cells involved.

Prevalence and incidence

There are no geographical, racial or social class boundaries. Anyone can be affected by seizures. Epilepsy can occur in both sexes of any age, especially infancy, childhood, adolescence and old age. In fact, up to 5% of the world's population may have a single seizure at some time in their lives. However, the diagnosis of epilepsy is reserved for those who have repeated seizures.

• The prevalence of a disorder is the proportion of a population with that disorder at a given point in time. The mean prevalence of active epilepsy (i.e. continuing seizures or the need for treatment) from many studies around the world is approximately 7 per 1 000 of the general population. Thus, 40 million people in the world have epilepsy at any one time.
• This may be an underestimate as some studies in developing countries (Colombia, Ecuador, Liberia, Nigeria, Panama, Tanzania and Venezuela) suggest a prevalence of more than 10 per 1 000.
  The lifetime prevalence of epilepsy, i.e. the number of people presently in the world who have epilepsy now or have had it in the past (e.g. childhood) or will get it in the future (e.g. old age), rises to approximately 100 million people.
• The incidence of a disorder is the number of new cases at a given time, usually one year. Studies in developed countries suggest an annual incidence of epilepsy of approximately 50 per 100 000 of the general population. However, studies in developing countries suggest this figure is nearly 100 per 100 000 (i.e. double).
• The main reasons for the higher incidence of epilepsy in developing countries are the higher risk of acute and chronic brain infections, pre- and post-natal obstetric complications, leading to brain damage, and malnutrition.

Mortality

Epilepsy is associated with an increased risk of mortality. Death may be related to:

• an underlying brain disease (e.g. tumour or infection);
• seizures in dangerous circumstances (drowning, burns, head injury, etc.);
• status epilepticus (frequent recurrent attacks without recovery of consciousness between each episode);
• sudden and unexplained causes, or a possible respiratory or cardio-respiratory arrest in seizure;
• suicide.

Studies are sparse, but in the UK epilepsy-related deaths in young adults are two to three times higher than standard age-related mortality rates. Mortality may be higher in developing countries due to either more serious brain diseases (e.g. infection) or absence of treatment. In a thirty-year follow-up of 164 patients in Tanzania, 67% of them died. The majority of deaths were related to epilepsy itself.

Syndromes

Epilepsy is characterized by seizures that can take many forms. Different epilepsy syndromes are based on the age of onset, the type of seizures, the presence or absence of detectable brain disease, and genetic background. Medical science is only at an early stage of this understanding.

SEIZURES may vary from the briefest lapses of attention or muscle jerks to severe and prolonged convulsions. Attacks may vary in frequency from less than one per year to several per day. Seizures are classified according to the site of the brain in which they arise. There are three broad categories:

• Generalised seizures: Seizures arising bilaterally and symmetrically in the brain. These will almost invariably involve loss of consciousness. They include the typical "grand mal" convulsion, and also the brief "absence", otherwise known as "petit mal".
• Partial or focal seizures: Seizures arising in one or more localized areas of the brain, which remain localized in that part of the brain.
• Partial or focal seizures which become generalized may spread to the whole brain, causing a generalized attack.
• The state of frequent recurrent attacks without recovery of consciousness between each episode is known as Status Epilepticus.

It is unclear why seizures occur at a particular age or time, and not at other ages and times. However, provocative factors are recognised in some patients - for example, certain flashing lights (discos, television, etc.), over-breathing, over-hydration, loss of sleep, emotional and physical stress may cause seizures. It is important to note that these are not causes of epilepsy, but they do influence the timing of seizures.

Causes

Epilepsy is often but not always the result of underlying brain disease. Any type of brain disease can cause epilepsy, but not all patients with the same brain disease will have epilepsy.

• There are still many people for whom the cause of their epilepsy cannot, as yet, be identified. In such cases, the theory most commonly accepted at present is that it is the result of an imbalance of certain chemicals in the brain, especially chemical messengers known as neurotransmitters.
• Children and adolescents are more likely to have epilepsy of unknown or genetic origin. The older the patient, the more likely it is that the cause is an underlying brain disease such as a brain tumour or cerebrovascular disease.
• Trauma and brain infection can cause epilepsy at any age and in particular, account for the higher incidence rate in developing countries. For example, in Latin America neurocysticercosis -- cysts on the brain caused by tapeworm infection -- is a common cause; in Africa AIDS and its related infections, malaria and meningitis; and in India AIDS, neurocysticercosis and tuberculosis.
• Febrile illness of any kind, whether or not it involves the brain, can trigger seizures in vulnerable young children, so-called febrile convulsions. About 5% of such children go on to develop epilepsy in later life.
• Furthermore, for any brain disease, only a proportion of sufferers will experience seizures as a symptom of that disease. It is, therefore, suspected that those who do experience such symptomatic seizures are more vulnerable for similar biochemical/neurotransmitter reasons.

Treatment and prognosis

Recent studies in both developed and developing countries have shown that up to 70% of newly diagnosed children and adults with epilepsy can be successfully treated (complete control of seizures for several years) with anti-epileptic drugs. After two to five years of successful treatment drugs can be withdrawn in about 70% of children and 60% of adults without relapses.

• Up to 30% of patients may not respond to drug therapy. There is evidence that the longer the history of epilepsy the harder it is to control. A factor which leads to a worse prognosis is the presence of an underlying brain disease. Partial seizures, especially if associated with brain disease, are more difficult to control than generalized seizures.
• For economic and social reasons, three out of four people in the world with epilepsy do not receive treatment at all, and most of these who do not receive treatment are in developing countries.
• Some forms of epilepsy, mainly but not only those related to acute short lasting disease of the brain such as infection or trauma, can run a self-limiting course. However, a significant proportion of patients with brain lesions go on to develop established epilepsy

Up to five per cent of mankind may have at least one seizure in their lives.

At any one point in time at least 40 million people have epilepsy, especially in childhood, adolescence and old age.

Epilepsy can have profound physical and psychological consequences, including sudden death, injuries and mood disorders.

In up to 70% of cases, epilepsy responds to treatment, but for economic and social reasons three out of four people in the world with epilepsy do not receive treatment at all.

For further information, contact WHO's Office of Public Information, Geneva. Telephone (41 22) 791 2584. Fax (41 22) 791 4858. E-Mail: inf@who.int

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