Temporal_lobe_epilepsy

Temporal lobe epilepsy Classification and external resources
ICD-10	G 40.1.-G 40.2.
ICD-9	345.4
DiseasesDB	29433
MedlinePlus	001399
eMedicine	neuro/365
MeSH	D004833

Temporal lobe epilepsy is a form of focal epilepsy, a chronic neurological condition characterized by recurrent seizures. While focal epilepsy accounts for about 50% of all epilepsy cases, the prevalence of temporal lobe epilepsy (TLE) among these cases remains uncertain.¹

Causes

Temporal lobe epilepsies are a group of medical disorders in which humans and animals experience recurrent epileptic seizures arising from one or both temporal lobes of the brain. Two main types are internationally recognized.

Because of strong interconnections, seizures beginning in either the medial or lateral areas often involve neighboring areas of the brain. The causes or etiology of different temporal lobe epilepsies vary.

A link between febrile seizures (seizures coinciding with episodes of fever in young children) and subsequent temporal lobe epilepsy has been suggested, but the exact role remains unclear.²³⁴⁵⁶ Some studies have shown abnormalities of the hippocampus on magnetic resonance imaging (MRI) in status epilepticus, which supports the theory that prolonged seizures damage the brain.⁷⁸⁹ Interestingly, some cases of MTLE present without the typical changes of mesial temporal sclerosis or other abnormalities on MRI scans. This has been termed paradoxical mesial temporal lobe epilepsy. The epilepsy in these patients tends to occur at a later age, which might suggest that an early event leads to hippocampal damage causing MTLE.¹⁰¹¹ Although this theory needs confirmation, some studies have pointed to human herpesvirus 6 (HHV-6) as a possible link between febrile convulsions and later MTLE. Firstly, several studies suggest that HHV-6 infection occurs commonly prior to the occurrence of febrile seizures.¹²¹³¹⁴¹⁵ However, only a minority of primary HHV-6 infections may be associated with febrile seizures.¹⁶ Secondly, other studies found HHV-6 DNA in brain tissue removed during surgery for MTLE.¹⁷¹⁸¹⁹²⁰

Rarely, MTLE can be hereditary or related to brain tumors, spinal meningitis, encephalitis, head injury or blood vessel malformations. MTLE can occur in association with other brain malformations. Most often, a cause cannot be determined with certainty.

LTLE is less common. It can be hereditary, as in Autosomal Dominant Lateral Temporal Lobe Epilepsy (ADLTLE) with auditory or visual features, but can also be associated with tumors, meningitis, encephalitis, trauma, vascular malformations or congenital brain malformations. Again, in many affected persons it is common that no cause can be identified.

Dispersion of granule cell layer in the hippocampal dentate gyrus is a major feature of temporal lobe epilepsy and is linked to the downregulation of reelin,²¹ ²² a protein that normally keeps the layer compact by containing the neuronal migration.

Symptoms

The symptoms felt by the patient with TLE and the signs observable by others during seizures depend upon the specific areas of the temporal lobes and neighboring brain areas affected by the seizure. The Classification of Epileptic Seizures published in 1981 by the International League Against Epilepsy (ILAE) recognizes three types of seizures which persons with TLE may experience.

Syndrome of Temporal Lobe Epilepsy (TLE)

The classical syndrome of TLE begins when there is a very early insult to the left or right hippocampus. Newborn babies may develop an infection resulting in a fever. Young babies have an immature thermoregulation system, and the fever causes the baby's core body temperature to increase. The raised body temperature can cause febrile convulsions. These are quite normal in babies, usually lasting only a few minutes, but in a few cases the convulsions can last for an hour. This is a sign that the infant is at a high risk of developing TLE.

Treatments

There are many oral medications available for the management of epileptic seizures, typically termed anticonvulsants or antiepileptic drugs (AEDs, for short). For temporal lobe epilepsy specifically, the most commonly used AEDs are (historically) phenytoin, carbamazepine, valproate and phenobarbital. Newer drugs, though, like gabapentin, topiramate,Levetiracetam and lamotrigine, promise similar efficacy with fewer side-effects. Nearly all AEDs function by decreasing the excitation of neurons (e.g., by blocking sodium channels or calcium channels) or by enhancing their inhibition (e.g., by potentiating the effects of inhibitory neurotransmitters, like GABA). Unfortunately, many patients with mesial temporal lobe epilepsy (up to one-third) will not experience adequate seizure control with medication.²³ For these patients, resective surgery is the primary alternative. In preparation for these surgeries, patients are monitored by various methods to determine the focus of their seizures (that is, the region of the brain where seizures tend to arise before spreading). This can be done with video-EEG monitoring, intracranial EEG (where electrodes are placed beneath the skull, either within or resting just outside the brain), or SPECT imaging. MRI studies may additionally be used to seek evidence of hippocampal sclerosis. Once the epileptic focus has been determined, it can be excised, which usually involves removing part of the hippocampus and often the amygdala. To avoid removing areas of the brain responsible for speech (so-called "eloquent" areas), the surgical team will conduct a Wada test pre-operatively, wherein sodium amytal is injected in the left or right carotid artery to effectively quiet one half of the brain. If the patient performs poorly on neuropsychological testing after the temporary quieting of a hemisphere, the surgical team will typically do their best to avoid operating on that area.

Social and artistic influence

Temporal Lobe Epilepsy and the Arts

As Eve LaPlante discusses in her book, "Seized," the intense emotions, sensory experience including vibrancy of colors, and particular mental state provoked by temporal lobe abnormalities may have contributed to the creation of significant works of art. A number of well-known writers and artists are known, or in many cases suspected to have had temporal lobe epilepsy, aggravated, in some cases, by alcoholism. They include Charles Dodgson (a.k.a. Lewis Carroll), Edgar Allan Poe, Fyodor Dostoevsky (whose novel The Idiot features an epileptic protagonist, Prince Myshkin), Gustave Flaubert, Philip K. Dick, Sylvia Plath and the contemporary author Thom Jones. Peter O'Leary also discusses this in his book "Gnostic Contagion: Robert Duncan and the Poetry of Illness." Sadi Ranson-Polizzotti writes about Lewis Carroll's epilepsy in many of her articles on Lewis Carroll on Tant Mieux and in her forthcoming book, publisher Continuum-Books, New York, London, Tokyo.

Temporal Lobe Epilepsy, Neurotheology and Paranormal Experience

The first researcher to note and catalog the abnormal experiences associated with TLE was neurologist Norman Geschwind, who noted a constellation of symptoms, including hypergraphia, hyperreligiosity, fainting spells, mutism and pedantism, often collectively ascribed to a condition known as Geschwind syndrome.

Vilayanur S. Ramachandran explored the neural basis of the hyperreligiosity seen in TLE using galvanic skin response, which correlates with emotional arousal, to determine whether the hyperreligiosity seen in TLE was due to an overall enhanced emotional response, or if the enhancement was specific to religious stimuli (Ramachandran and Blakeslee, 1998). By presenting subjects with neutral, sexually arousing and religious words while measuring GSR, Ramachandran was able to show that patients with TLE showed enhanced emotional responses to the religious words, diminished responses to the sexually charged words, and normal responses to the neutral words. These results suggest that the medial temporal lobe is specifically involved in generating some of the emotional reactions associated with religious words, images and symbols.

Temporal lobe epilepsy and orgasms

In some modes of presentation women can experience orgasms when suffering a temporal lobe epilepsy episode. No cases have so far been reported for men.²⁴

Contents

Causes

Symptoms

Syndrome of Temporal Lobe Epilepsy (TLE)

Treatments

Social and artistic influence