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Structural and Genetic Temporal Lobe Epilepsy – Hippocampal Sclerosis
Mesial Temporal vs.Lateral Temporal Lobe Epilepsy – Structural vs. Genetic Autosomal Dominant –Diagnosis – Treatment – Prognosis – Surgery for Temporal Lobe Epilepsy
Structural vs. Genetic Temporal Lobe Epilepsy
Structural/Metabolic, former symptomatic, epilepsy term is referring to epileptic seizures occurring secondary to physical or metabolic insult on the brain tissue. Focal epilepsy is not likely to be caused by metabolic abnormalities, though. Developmental brain anomalies, neuronal migration disorders, arteriovenous malformations, venous angiomas, strokes, tumors, infections, or head injuries are the most common causes of structural epilepsy.
Genetic and structural forms of temporal lobe epilepsy have similar symptoms. In genetic forms, however, there should be no evidence of temporal lobe structural abnormalities on the MRI.
Response to anti-epileptic medication is less robust in structural forms of temporal lobe epilepsy as compared to genetic forms.
Surgery is reserved exclusively for proven structural temporal lobe epilepsy. Surgical removal of the diseased brain area in structural epilepsy is a viable and often better treatment option. Surgery may cure or significantly moderate seizure severity and frequency.
If untreated, some focal epilepsy syndromes, such as hippocampal sclerosis, may worsen over time. The individual prognosis is usually unpredictable, however. There is some difference in treatment success, depending on the cause and location of the epileptic focus. There is usually no specific age of onset or gender predominance in temporal lobe epilepsy.
Postictal symptoms are typically severe in structural temporal lobe epilepsy. Partial complex status epilepticus is not common in genetic temporal lobe epilepsy but is not unusual in structural epilepsy, especially in untreated patients.
Symptoms of temporal lobe epilepsy depend on the epileptic focus location in the mesial vs. lateral temporal lobe.
Mesial Temporal Lobe Epilepsy with Hippocampal Sclerosis
It is one of the most common types of epilepsy, or about 20% of all epilepsies, 65% of patients with temporal lobe epilepsy, and 80% with mesial temporal lobe epilepsies have hippocampal sclerosis. There is no gender predominance. Age of onset varies from infancy to early thirties with 80% developing seizures before age 16.
History of febrile seizures is present in about 60%, with complex febrile seizures in 35%. Prolonged beyond typical febrile seizures are especially associated with temporal lobe epilepsy. Genetic predisposition probably plays a role in some families.
Hippocampal sclerosis is the most common cause of structural temporal lobe epilepsy. The cause of hippocampal sclerosis remains elusive. There are a few proposed mechanisms of nerve cell loss in the hippocampus: developmental anomalies, autoimmune disease, and overstimulation by repetitive or prolonged seizures. Some evidence exists that abnormalities in the brain are spread well beyond the temporal lobe.
The most common focal seizure manifestation is a rising epigastric sensation associated with fear. It is described as a bizarre nauseating/emptying/unpleasant sensation that starts from the upper abdomen gradually moving upwards. This type of focal seizure is not typical for genetic mesial temporal lobe epilepsy.
Automatisms occur in about 70%. They are repetitive, stereotypical purposeless movements: chewing, lip smacking, picking, fidgeting. Automatisms may be limited to one side.
Complex partial seizures usually present with arrest of normal activity, staring, and may be accompanied by automatisms. They last from 30 seconds to 2 minutes and may be confused with absences. There is lack of awareness and response to the surrounding. Complex partial status epilepticus may occur in some patients.
Complex internal sensations of déjà vu spectrum and hallucinations of taste and smell are less common.
Generalized tonic-clonic seizures, as a secondary phenomenon, occur mostly in untreated patients.
Postictal state (period of confusion after seizure) is typical.
Diagnosis of Mesial Temporal Epilepsy
Brain MRI demonstrates hippocampal sclerosis. Additional developmental anomalies may be seen in some patients.
Interictal EEG is non-revealing in half of the patients on a single recording.
Only one third have a classical sharp-and-slow wave epileptic focus in the temporal lobe. Sleep deprivation and lengthy monitoring increases sensitivity up to 80%. Half of the patients have runs of slow waves in the temporal region.
Ictal EEG: 4 to 7 Hz rhythmic slow wave activity over the temporal lobe.
Prognosis and Treatment
The prognosis is unpredictable in each particular patient. In some patients initial response to medications may moderate over years leading to progressive worsening of seizure severity and frequency. Intractable epilepsy may lead to memory and psychological abnormalities.
In the majority of hippocampal sclerosis cases response to anti-epileptic drugs remains substantial for years. Any antiepileptic medications indicated for focal seizures (see at the bottom of the page) or their combinations may be employed in seizure control. The choice is dictated by age, gender, and other medical problems.
For intractable epilepsy, surgery in an excellent alternative, since 60% will become seizure free, 10% will have no reduction in seizure frequency, and 20% will have some degree of improvement.
Surgical intervention involves the removal of a large portion of the temporal lobe. For this reason, about 10% will have surgical complications (speech and memory problems are the main concerns) or get worse.
Structural Lateral Temporal Lobe Epilepsy
Lateral temporal lobe epilepsy is about 2 times less common than mesial. It is equally common in males and females and usually starts in adolescent years.
Hallucinations: hearing of sounds, vertigo, visual hallucinations and illusions, déjà vu, jamais vu
Motor seizures: hand automatisms, grimacing, clonic movements in the face, arm posturing, vocalizations, whole body rotation, speech disturbance
Complex partial seizures or complex partial status epilepticus and secondary GTCS are possible in untreated patients.
There is less impairment of consciousness than in mesial temporal lobe epilepsy.
Diagnosis of Lateral Temporal Epilepsy
Brain MRI is abnormal in the majority of patients.
Inter-ictal EEG is often abnormal with focal slow waves and spikes over the affected temporal lobe.
Ictal EEG demonstrates 4 to 7 Hz rhythmic activity or fast spiking in the leads over the affected temporal lobe.
Prognosis and Treatment of Lateral Temporal Epilepsy
The prognosis largely depends on the cause of the brain lesion and is not very predictable. Medications for focal seizures produce variable response which is predictably worse than in genetic form of temporal lobe epilepsy. Surgical treatment is a potentially curative option for this type of epilepsy.
Familial Autosomal Dominant Lateral Temporal Lobe Epilepsy
Simple auditory hallucinations is the hallmark of focal epilepsy arising from the lateral temporal lobe: different noises, buzzing, clicking, or humming. The focal seizures may progress to complex partial seizures and to GTCS, but it is not very common.
Less frequent are primitive visual hallucinations (figures, blobs of colors), speech arrest, vertigo, and smells. Seizures may be provoked by sleep. The type of seizures points to the source of epileptic activity in the lateral portion of the temporal lobe.
Typical age of onset is second or third decade. No sex preferences.
Autosomal Dominant with 80% penetrance. Mutation of LGI1/Epitempin gene in chromosome 10q.
Brain imaging is unremarkable. EEG is usually normal. Presence or normal brain imaging and family history distinguish this syndrome from secondary/structural temporal lobe epilepsy.
Prognosis and Treatment
There are no neurological or mental health sequelae. Seizures are usually brief, infrequent and mild. There is excellent response to Carbamazepine.
Familial Mesial Temporal Lobe Epilepsy
Considering location of the brain memory domain in the mesial temporal lobe, the whole range of subjective internal and perceptual phenomena, as well as autonomic symptoms is possible in this epilepsy syndrome: déjà vu, jamais vu, “stranger behind the back”, feeling of detachment from oneself, sensation of enlightenment, extreme pleasure, fear and dread, anxiety, nausea, vomiting, paleness, palpitations, and so on.
Other symptoms are illusions of vision and hearing, strange, hard to localize and describe body sensations. A focal seizure may infrequently progress to GTCS.
Age of onset is the second to third decade with median age of 25 years. It is slightly more common in females.
Autosomal dominant with about 60% penetrance. Multiple genetic mutations appear to be involved.
Brain imaging is usually normal but some T2 hyperintensities in the temporal lobes may be seen on the Brain MRI. FDG-PET may demonstrate hypometabolism in the temporal lobe.
The main issue is a differentiation from hippocampal sclerosis, which may also be familial.
Interictal EEG is normal in 50%. The rest have either slow- or sharp-and-slow wave discharges over a temporal lobe (usually on one side). Ictal EEG usually demonstrates epileptiform activity over the temporal areas.
Prognosis and Treatment
The course of autosomal dominant focal epilepsy is variable. Some patients with mild symptoms will never know that they have an epilepsy, unless they have family history with more severe forms.
A small percentage has severe epilepsy with poor response to antiepileptic drugs.
The majority has an obvious epilepsy syndrome with some of the attacks progressing to complex partial seizures or GTCS; with excellent response to treatment.
Long remissions with subsequent seizure recurrence are common. Good response to Carbamazepine or other AED indicated for focal seizures, as described at the bottom of the page.
Familial Focal Epilepsy with Variable Foci
This is an epileptic syndrome running in families which does not have a structural counterpart for obvious reasons.
Variable types of focal epilepsy which may arise from any of brain areas: frontal, temporal, parietal, or occipital. Even though each particular patient has a fixed epileptic focus in a particular brain region, the location is not specific for the rest of the family members. Each one has a unique focus location. This means that symptoms in every person affected are different.
The only feature they share is the fact that everyone has some form of focal seizures with or without progression to complex partial seizure and GTCS. The majority has generalized tonic-clonic seizures.
Seizures in sleep are common. Both sexes are affected equally. The age of onset varies from infancy to early 40s, with median 10 years.
Autosomal dominant with 60% penetrance. Multiple genetic abnormalities in chromosomes 22 and 2 are involved.
Brain imaging is expected to be normal.
EEG, ictal and interictal, show focal epileptic discharges in different areas. Location of the epileptic focus is specific for every particular patient and this location is not changing over time.
EEG abnormalities can be brought up by sleep and may be present in asymptomatic family members.
The extent of EEG changes is not indicative of severity or prognosis of the epilepsy syndrome.
Prognosis and Treatment
Epilepsy syndrome severity and response to treatment vary from family to family and from patient to patient within the same family.
The response to anti-epileptic drugs is usually decent.
Treatment of Autosomal Dominant Focal Epilepsy Syndromes
Most of familial focal epilepsies demonstrate a very good response to Carbamazepine. If Carbamazepine is not effective, poorly tolerated or contraindicated, any other anti-epileptic drug for focal epilepsy (or drug combination) may be employed for seizure control.
Depending on side effects profiles, gender, age and other medical conditions the following medications are reasonable choices: Oxcarbazepine, Pregabalin, Gabapentin, Lamotrigine, Levetiracetam, Tiagabine, Topiramate, and Zonisamide.
The same medications are indicated in structural temporal lobe epilepsy.