Temporal Lobe Epilepsy Health Article

Definition

Temporal lobe epilepsy (TLE) is a term that refers to a condition where seizures are generated in the portion of the brain called the temporal lobe. Either the right or the left temporal lobe can be involved, and in rare cases both temporal lobes can be involved in a particular individual.

Description

Under the broad category of TLE, there are a number of specific types. In mesial TLE (MTLE), there are characteristic abnormalities in the mesial aspect of the temporal lobe. This variably involves sclerosis (scarring), loss of nerve cells in the hippocampus and mossy cell fiber sprouting. Of course, there are other different pathologies that can be seen in the temporal lobe including tumors, stroke, multiple sclerosis plaques, and tubers (as seen in tuberous sclerosis). Another type of TLE is lateral TLE. This is where the seizures originate in the lateral portion of the particular temporal lobe. Again, various pathologies can be found such as cortical malformations and stroke. However, imaging studies, such as magnetic resonance imaging (MRI), often may not show any obvious lesions or abnormalities. As more information is gathered regarding the genetics that may be involved in some cases, the classification of TLE will likely change.

Demographics

TLE, as a whole, constitutes a common type of epilepsy. The exact incidence is not clear but it is suspected to make up a significant proportion of medication-resistant epilepsy. Approximately 30% (of the 2.7 million cases of epilepsy in the United States) do not adequately respond to medications. Up to a half of these may be due to TLE. One of the risk factors that may predispose children to, in particular, mesial TLE is complicated or prolonged febrile convulsions before the age of five years. Mesial TLE can also run in some families.

Causes and symptoms

The abnormalities most associated with mesial TLE are sclerosis (scarring) of the hippocampus, neuronal cell loss in the hippocampal area, and inappropriate sprouting (growth) of mossy cell fibers. The cause of these variable pathological findings is still being studied. There is some evidence that mesial TLE may be a progressive condition where seizures become more resistant to medications over time. Likely, seizures over time play a role in the changes seen in the mesial temporal lobe. Likewise, the mesial temporal abnormalities contribute to the epileptogenicity (seizure potential) of that region. Although these pathologies are the most common findings in cases of mesial TLE, other lesions can be the suspected cause of epilepsy such as stroke, multiple sclerosis plaques, tumors, and cortical malformations. Lateral TLE can also be affected by strokes, cortical malformations, multiple sclerosis plaques, etc., and be the cause of seizures from this area. In the rare condition of benign familial TLE the cause is genetic and runs in families. Exactly how any of the previously mentioned abnormalities actually cause groups of neurons to generate seizure activity is complex and not fully under-stood. Because there can be different lesions, there can also be different mechanisms of generating a seizure. The temporal lobe epilepsies should not be considered as diseases. Rather, they are syndromes (groups of physical signs and symptoms) with many causes.

The age of onset of TLE is highly variable depending on the cause. In mesial TLE, seizure can begin as early as childhood or even later in adulthood. There is a characteristic remission that can occur during childhood, lasting a few years, but then seizures resume in adulthood.

The seizures that occur in TLE are simple partial seizures or complex partial seizures. Uncommonly, a generalized tonic-clonic seizure may occur. The simple partial seizures can take the form of auras. Although these are viewed as seizure warnings, they are actually minor seizures that do not affect consciousness. The most common aura is a visceral sensation. This can take the form of a rising feeling in stomach. Other kinds of auras can be déjà vu (a sense of familiarity) or jamais vu (the opposite of déjà vu, a sense of unfamiliarity or uniqueness); distortion of perceptions of size, or movement (vertigo); or olfactory (odors) distortions and buzzing sounds depending on what portion of the temporal lobe is involved. Emotional auras can also occur; fear, for example. Still other auras are too difficult for patients to describe. All these minor seizures are usually not serious unless they are occurring frequently and are disturbing to the person.

Seizures that affect or alter consciousness are present in the majority of people with TLE. These complex partial seizures variably involve cessation of activity, a certain degree of starring off, lip smacking or other oral movements. Moreover, the arm contralateral (opposite) the temporal lobe displays a posturing action. The arm ipsilateral (same side) as the affected temporal lobe has automatisms (semi-purposeful motions). During this phase of the seizure, the person has little to no awareness of the environment and will virtually be unresponsive to those around him or her. The aura plus the complex-partial-seizure phase typically lasts less than two to three minutes. Then there is a variable period of confusion lasting longer. If the seizure involves primarily the dominant (usually left) hemisphere (where language is processed) then a so-called post-ictal (after seizure) aphasia (loss of language) can occur and last several minutes. All these behavioral features can help decide which hemisphere, if not temporal lobe, is involved.