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Epilepsy: aetiogy, epidemiology and prognosis
What is epilepsy?
Epilepsy is a neurological disorder that affects people in every country throughout the world. Epilepsy is also one of the oldest conditions known to mankind. It is characterized by a tendency to recurrent seizures and it defined by two or more unprovoked seizures.
The belief widely held in many countries is 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" being derived from the Greek word "epilambanein" which means "to seize or attack". We now know, however, that seizures are the result of sudden, usually brief, excessive electrical discharges in a group of brain cells (neurones) and that different parts of the brain can be the site of such discharges. The clinical manifestations of seizures will therefore vary and depend on where in the brain the disturbance first starts and how far it spreads. Transient symptoms can occur, such as loss of awareness or consciousness and disturbances of movement, sensation (including vision, hearing and taste), mood or mental function.
Seizures may vary from the briefest lapses of attention or muscle jerks to severe and prolonged convulsions. They may also vary in frequency, from less than one a year to several per day. Seizures are classified according to where in the brain they arise, for instance:
These seizures arise from an electric discharge of one or more localised areas of the brain regardless of whether the seizure is secondarily generalized. Depending on their type, they may or may not impair consciousness. Whether seizures are partial or focal, they begin in a localized area of the brain, but then may spread to the whole brain causing a generalized seizure.
The electrical discharge which leads to these seizures involves the whole brain and may cause loss of consciousness and/or muscle contractions or stiffness. They include what used to be known as "grand mal" convulsion and also the brief "petit mal" absence of consciousness.
This is a state in which a person has frequent seizures without recovery of consciousness between each episode. It is a dangerous state and if not treated may lead to brain damage or death.
It is unclear why particular seizures occur at a particular age or time and not at other ages or times. Provocative factors, however, are recognized in some patients. For example, certain flashing lights (discos, television, video games etc.), over-breathing, over-hydration, loss of sleep, and/or emotional and physical stress, may stimulate seizures. Although these are not causes of epilepsy, they may influence the timing and frequency of seizures.
Different epileptic syndromes are based on the age of onset, the type of seizure, the presence or absence of detectable brain disease and genetic background. However, medical science is only at an early stage in understanding these different types.
Epidemiology: prevalence, incidence and mortality of epilepsy
Epilepsy knows no geographical, racial or social boundaries. It occurs in men and women and can begin at any age, but is most frequently diagnosed in infancy, childhood, adolescence and old age. Anyone can be affected by seizures. In fact, up to 5% of the world's population may have a single seizure at some time in their lives, but a diagnosis of epilepsy is reserved for those who have recurring seizures, at least two unprovoked ones.
The prevalence of a disorder is the proportion of a population with that disorder at a given point in time. From many studies around the world it has been estimated that the mean prevalence of active epilepsy (i.e. continuing seizures or the need for treatment) is approximately 8.2 per 1,000 of the general population. However, this may be an underestimate as some studies in developing countries (such as Colombia, Ecuador, India, Liberia, Nigeria, Panama, United Republic of Tanzania and Venezuela) suggest a prevalence of more than 10 per 1,000.
The incidence of a disorder is the number of new cases at a given time. 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 that this figure is nearly double that at 100 per 100,000.
One of the main reasons for the higher incidence of epilepsy in developing countries is the higher risk of experiencing a condition which can lead to permanent brain damage. These conditions include 1neurocysticercosis, meningitis, malaria, pre and perinatal complications and malnutrition.
Epilepsy is associated with an increased risk of mortality. Death may be related to:
Whilst studies on this subject are sparse, epilepsy-related deaths in young adults in the UK, for example, are 3 times higher than standard age-related mortality rates.
Etiology of epilepsy
Epilepsy is often, but not always, the result of an underlying brain disease. Any type of brain disease can cause epilepsy, but not all people with the same brain disease will have epilepsy. In view of the fact that only a proportion of people who have a brain disease experience seizures as a symptom of that disease, it is suspected that those who do have such symptomatic seizures are more vulnerable due to 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 (i.e, their seizures can be completely controlled for several years) with anti-epileptic drugs. After 2-5 years of successful treatment, drugs can be withdrawn in about 70% of children and 60% of adults without relapses.
Sources: US Department of Health; The World Health Organization