Epilepsy

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All the causes (or etiologies) of epilepsy are not known, but many predisposing factors have been identified, including brain damage resulting from malformations of brain development, head trauma, neurosurgical operations, other penetrating wounds of the brain, brain tumor, high fever, bacterial or viral encephalitis, stroke, intoxication, or acute or inborn disturbances of metabolism. Hereditary or genetic factors also play a role.

Seizures may occur in any person under certain circumstances, including acute illness and drug overdoses, but these provoked seizures are not part of the definition of epilepsy. Epilepsy connotes that an individual has unprovoked seizures which recur over time. In about 50% of all cases, there is no cause for epilepsy that is currently detectable even with state of the art investigations. In about 50% of cases, evidence of a brain injury, scar or malformation is found, to which the epilepsy is attributed. In many, but not all cases, abnormal electrical activity can be detected in the brain with an electroencephalogram (EEG), either during or in between seizures.

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The most common ages of incidence are under the age of 18 and over the age of 65. It has been estimated that about 1% of the population meets the diagnostic criteria for epilepsy at any given time, but some theorize that the prevalence may be much higher in fact.

A significant and measurable decline in cognitive function is known to be associated with epilepsy, although it has not been entirely clear to what extent this is due to the epilepsy itself or to the drugs used to treat it. Phenobarbital, in particular, has been shown to decrease IQ and classroom performance when used to treat epilepsy in children; the effects persist after the phenobarbital is stopped. Some newer anti-epileptic drugs are considered by some to have less severe cognitive effects than older drugs. On an individual level, a person's reaction to epileptic seizures and/or anti-epileptic drugs may be idiosyncratic, so it is difficult to predict how a particular person might be affected.

Mutations in several genes have been linked to some types of epilepsy. Several genes that code for protein subunits of voltage-gated and ligand-gated ion channels have been associated with forms of generalized epilepsy and infantile seizure syndromes[2]. Several ligand-gated ion channels have been linked to some types of frontal and generalized epilepsies. Epilepsy-related mutations in some non-ion channel genes have also been identified.

One interesting finding in animals is that repeated low-level electrical stimulation to some brain sites can lead to permanent increases in seizure susceptibility: in other words, a permanent decrease in seizure "threshold." This phenomenon, known as kindling (by analogy with the use of burning twigs to start a larger fire) was discovered by Dr. Graham Goddard in 1967. Chemical stimulation can also induce seizures; repeated exposures to some pesticides have been shown to induce seizures in both humans and animals. One mechanism proposed for this is called excitotoxicity. The roles of kindling and excitotoxicity, if any, in human epilepsy are currently hotly debated.

"Normal" provocants

Some people with epilepsy have certain triggers or provocants that will reliably produce a seizure. If the provocant can reasonably considered to be part of normal daily life, and yet it causes a seizure, the seizures are considered 'unprovoked' for the purpose of diagnosing the person with epilepsy. Examples of these "normal provocants" include reading, hot water on the head, hyperventilation, and flashing lights.

For example, some people (especially young children) have seizures when exposed to certain patterns of flashing/flickering lights. This is a special type of reflex epilepsy called photosensitive epilepsy. (Such seizures are often informally called "Pokémon seizures," after an article was published describing an outbreak of photosensitive seizures due to broadcast of an episode of the popular children's television show Pokémon. While some of the children involved doubtless had photosensitive epilepsy, some investigators believe that the majority of the 12,000 affected in this outbreak actually were having psychogenic non-epileptic seizures.)

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