Causes of Epilepsy

Seizures are symptoms of abnormal brain function. With the exception of very young children and the elderly, the cause of the abnormal brain function is usually not identifiable.

However, when seizures start, the physician will try to identify an underlying etiology (cause). This is because the most specific diagnosis as to why seizures are occurring depends on finding a cause, and the best therapy will be one specific to the etiology.

If a specific diagnosis of cause cannot be made, then the epilepsy will be described according to seizure type or epileptic syndrome.

Symptomatic seizures are so named when they can be linked to identifiable diseases or brain abnormalities.

Cryptogenic, idiopathic or primary seizures are diagnosed when no cause for the seizures can be found. When it is necessary to classify epilepsy according to cause, similar terms are used.

Causes of seizures (and sometimes epilepsy) are further divided into acute and remote causes. This subclassification depends on whether there is active brain disease (an acute cause) or whether the brain abnormality is the result of an injury caused by a previous event (in which case it would be called remote). For example, if a child with meningitis experiences seizures during the illness, they would be termed acute symptomatic seizures. If that same child developed seizures that persisted for years afterwards, she would be diagnosed as having remote symptomatic epilepsy.

Many acute symptomatic causes of seizures may, if severe enough, continue to produce recurring seizures (chronic epilepsy) later on.

Head trauma is an important cause of seizures and epilepsy. Although it is commonly accepted that a remote injury (that is, one which occurred at some time in the past) can cause epilepsy, there is no agreement on how extensive or of what type that injury must be. It is known that the risk for epilepsy increases substantially if there are open or penetrating wounds, however. On the other hand, trauma that produces only brief or no loss of consciousness does not predispose to epilepsy, nor does a minor head injury. Sometimes several years will pass between the original injury and the development of seizures and epilepsy.

Genetic factors. People with first-degree relatives (parents or siblings) who have epilepsy are at increased risk of developing seizures themselves. A family history of epilepsy may be considered a risk factor for epilepsy in the same way that brain injury or prior meningitis is a risk factor. However, while some epilepsy appears to be directly inherited, the risk does not follow classic Mendelian principles. Brain function—from cell membrane to level of neurotransmitter substances to other biochemical mechanisms—is controlled by individual genes that, if damaged or mutant, may lead to seizures. The search is on for genes which may be directly linked to a specific type of epilepsy. Recent discoveries in this area include a gene associated with progressive myoclonic epilepsy, and the gene for absence epilepsy in mice.