Frontal lobe epilepsy

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Brain: Frontal lobe

Principal fissures and lobes of the cerebrum viewed laterally. (Frontal lobe is blue.)
Gray726 central sulcus.svg
Lateral surface of left cerebral hemisphere, viewed from the side. Red line indicates the central sulcus.
Latinlobus frontalis
Gray'sp.821
NeuroNameshier-29
NeuroLex IDbirnlex_4035
 
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Frontal lobe epilepsy, or FLE, is a neurological disorder that is characterized by brief, recurring seizures that arise in the frontal lobes of the brain, often while the patient is sleeping. It is the second most common type of epilepsy after temporal lobe epilepsy (TLE), and is related to the temporal form by the fact that both forms are characterized by the occurrence of partial (focal) seizures. Partial seizures occurring in the frontal lobes can occur in one of two different forms: either simple partial seizures (that do not affect awareness or memory) or complex partial seizures (that affect awareness or memory either before, during or after a seizure). The symptoms and clinical manifestations of frontal lobe epilepsy can differ depending on which specific area of the frontal lobe is affected.[1]

The onset of a seizure may be hard to detect since the frontal lobes contain and regulate many structures and functions about which relatively little is known. Due to the lack of knowledge surrounding the functions associated with the frontal lobes, seizures occurring in these regions of the brain may produce unusual symptoms which can often be misdiagnosed as a psychiatric disorder, non-epileptic seizure or a sleep disorder.[2]

During the onset of a seizure, the patient may exhibit abnormal body posturing, sensorimotor tics, or other abnormalities in motor skills.[2] In rare cases, uncontrollable laughing or crying may occur during a seizure.[1] Afflicted persons may or may not be aware that they are behaving in an abnormal manner, depending on the patient and type of seizure. A brief period of confusion known as a postictal state may sometimes follow a seizure occurring in the frontal lobes. However, these postictal states are often undetectable and generally do not last as long as the periods of confusion following seizures that occur in the temporal lobes.

There are many different causes of frontal lobe epilepsy ranging from genetics to head trauma that result in lesions in the frontal lobes. Although frontal lobe epilepsy is often misdiagnosed, tests such as prolonged EEG monitoring and/or a MRI scan of the frontal lobes can be administered in order to reveal the presence of a tumor or vascular malformation. Unlike most epileptic EEGs, the abnormalities in FLE EEGs precede the physical onset of the seizure and aid in localization of the seizure's origin.[3] Medications such as anti-epileptic drugs can typically control the onset of seizures, however, if medications are ineffective the patient may undergo surgery to have focal areas of the frontal lobe removed.

Signs and symptoms[edit]

Epileptic symptoms are frequently the product of the spread of overactivation occurring within one central foci that travels to lateral brain regions thereby causing an array of symptoms. Due to the massive amount of diversity in both the cognitive and motor functions that occur within the frontal lobes, there is an immense variety in the types of symptoms that can arise from epileptic seizures based on the side and topography of the focal origin. In general these symptoms can range anywhere from asymmetric and abnormal body positioning to repetitive vocal outburts and repetitive jerking movements.[2] The symptoms typically come in short bursts that last less than a minute and often occur while a patient is sleeping.[4] In most cases, a patient will experience a physical or emotional Aura of tingling, numbness or tension prior to a seizure occurring.[5] Fear is associated with temporal and frontal lobe epilepsies, but in FLE the fear is predominantly expressed on the person's face whereas in TLE the fear is subjective and internal, not perceptible to the observer.[3]

Tonic posture and clonic movements are common symptoms among most of the areas of the frontal lobe, therefore the type of seizures associated with frontal lobe epilepsy are commonly called tonic-clonic seizures. Dystonic motor movements are common to both TLE and FLE, but are usually the first symptom in FLE episodes where they are quite brief and do not affect consciousness. The seizures are complex partial, simple partial, secondarily generalized or a combination of the three. These partial seizures are often misdiagnosed as psychogenic seizures.[3] A wide range of more specific symptoms arise when different parts of the frontal cortex are affected.[1]

Common misdiagnoses[edit]

Episodes that include complex hyperactivity of the proximal portions of the limbs that lead to increased overall motor activity are called hypermotor seizures. When associated with bizarre movements and vocalizations these seizures are often misdiagnosed as pseudoseizures or other episodic movement disorders such as psychogenic movement disorders, familial paroxysmal dystonic choreoathetosis, paroxysmal kinesogenic choreoathetosis, or episodic ataxia type 1.[3] Hypermotor seizure in children are often confused with pavor nocturnus (night terrors). Paroxysmal nocturnal dystonia or hypnogenic paroxysmal dystonia are other names given to describe FLE symptoms but are simply just FLE.[3]

Autosomal Dominant Nocturnal Frontal Lobe Epilepsy (ADNFLE) is the best understood form of frontal lobe epilepsy but is often misdiagnosed as sleep apnea. Both disorders are characterized by awakening during the night which leads to daytime sleepiness. Some symptoms of sleep apnea overlap with those of ADNFLE, such as sudden awakening accompanied by a feeling of choking and on occasion motor activity which makes diagnosis difficult based on symptoms alone. Video surveillance as well as EEG is occasionally needed to differentiate between the two disorders. It has been reported that sleep apnea might be associated with epilepsy which would account for some of the misdiagnoses.[3]

Causes[edit]

An MRI image of a brain with an invasive, multilocular tumor in the left Frontal lobe of the brain.

The origins of frontal lobe seizures range from tumors to head trauma to genetics. Tumors account for about one third of all frontal lobe epilepsy cases. Low-grade tumors such as gangliogliomas, low-grade gliomas, and epidermoid tumors are most common, but many high-grade tumors were most likely once involved with seizures. Other lesions on the frontal lobe such as hamartomas and nodular heterotopias can cause frontal lobe symptoms as well. Birth defects such as vascular malformation are known to cause seizures, especially arteriovenous malformations and cavernous angiomas. Head trauma frequently causes damage to the frontal lobe and can cause seizures directly or indirectly through gliosis. Seizures originating directly from head trauma usually occur within a few months, but occasionally they can take years to manifest. On occasion encephalitis can cause frontal lobe seizures but it is most often associated with temporal lobe affliction. The main genetic cause of frontal lobe epilepsy is an autosomal dominant disease called Autosomal Dominant Nocturnal Frontal Lobe Epilepsy, which involves mutations in 2 nicotinic acetylcholine receptor genes. A genetic mutation on chromosome 22 has also been associated with another genetic form of the disorder.[1]

Mechanism[edit]

Due to the difference in brain processing and function as well as various surface anatomy landmarks, the frontal lobes have traditionally been divided into two major areas known as the precentral cortex and prefrontal cortex.

Brain: Frontal lobe

Principal fissures and lobes of the cerebrum viewed laterally. (Frontal lobe is blue.)
Gray726 central sulcus.svg
Lateral surface of left cerebral hemisphere, viewed from the side. Red line indicates the central sulcus.
Latinlobus frontalis
Gray'sp.821
NeuroNameshier-29
NeuroLex IDbirnlex_4035

Precentral cortex[edit]

The precentral cortex is an area of the frontal cortex that is located directly anterior to the central sulcus and includes both the primary motor cortex and the supplementary motor area.[5] Inputs that project to both of these areas arise from a variety of locations in the brain that integrate sensory stimuli including the primary motor cortex, the thalamus and corticospinal projections.[5]These two areas along with several other main functional areas control both the preparation of motor movement as well as the execution of movements. These main functional areas are crucial to the development of the motor related symptoms associated with frontal lobe epilepsy focally when seizures are located within these defined areas.[6] The major functional areas include:

Prefrontal cortex[edit]

The prefrontal cortex, the most anterior region of the brain, comprises several key areas that are particularly important for higher mental functions that control various aspects of human personality including anticipation and planning, initiative/judgement, memory and the control of decision making.[9] Damage or lesions to this region of the brain can result in major changes in personality. A classic example is Phineas Gage, who exhibited a change in behavior after one or both frontal lobes were destroyed by a large iron bar accidentally driven through his head (though Gage, despite conventional presentations of his case, did not exhibit the aggression, antiosocial behavior, or loss of impulse control sometimes reported in patients with similar injuries).

There are two main regions of the prefrontal cortex that each control various aspects of behavior and personality:

Social effects and quality of life[edit]

Epilepsy has a substantial impact on the quality of life of the individuals that are afflicted with it. Physicians and researchers are coming to understand that the impact on the quality of life of the patient is as important as the effects of the seizures.[11] Quality of life questionnaires and other assessment tools have been created to help quantify quality of life for individual patients. They consider such factors as physical health (including numbers and severity of seizures, medication side effects etc.), mental health, social relationships, lifestyle, role activities and life fulfillment.[12] A Center for Disease Control study reported that seizure sufferers were more likely to have lower education levels, higher unemployment, higher levels of pain, hypersomnia/insomnia, increased psychological distress and social isolation/connection issues.[13] Some of the issues which impact quality of life for people with epilepsy are: ability to drive and travel, the ability to date, marry and have children, the ability to have a job and independence, the ability to have an education and learn, and the ability to have good health and mental functioning.[14] Future research is needed to find ways to not only control frontal lobe seizures, but to also address the specific quality of life issues that plague those with frontal lobe epilepsy.

Driving and transportation restrictions
Hormones and pregnancy issues
Employment
Education, learning and cognitive function
Physical health and risk of other conditions
Mental and emotional health

Treatments[edit]

There are several different ways to treat frontal lobe epileptic seizures, however, the most common form of treatment is through the use of anticonvulsant medications that help to prevent seizures from occurring. In some cases, however, when medications are ineffective, a neurologist may choose to operate on the patient in order to remove the focal area of the brain in which the seizures are occurring. Other treatments that can be administered to aid in reducing the occurrence of seizures include the implementation of a specific, regimented diet and/or the implantation of a vagus nerve stimulator.

Medications[edit]

Anticonvulsants are the most successful medication in reducing and preventing seizures from reoccurring. The goal of these medications in being able to reduce the reoccurrence of seizures is to be able to limit the amount of rapid and extensive firing of neurons so that a focal region of neurons cannot become over-activated thereby initiating a seizure. Although anticonvulsants are able to reduce the amount of seizures that occur in the brain, no medication has been discovered to date that is able to prevent the development of epilepsy following a head injury. There are a wide range of anticonvulsants that have both different modes of action and different abilities in preventing certain types of seizures. Some of the anticonvulsants that are prescribed to patients today include: Carbamazepine (Tegretol), Phenytoin (Dilantin Kapseals), Gabapentin (Neurontin), Levetiracetam (Keppra), Lamotrigine (Lamictal), Topiramate (Topamax), Tiagabine (Gabitril), Zonisamide (Zonegran) and Pregabalin (Lyrica).[1]

Surgical treatment[edit]

When both the amount and severity of seizures becomes uncontrollable and seizures remain resistant to the various anticonvulsants, a patient most likely will be considered for epilepsy surgery such as a frontal lobectomy.[30] This procedure involves the removal of focal regions of the frontal lobes that have been identified as being problematic for the patient. It has been found that around 30% to 50% of patients that undergo a frontal lobectomy will forever be free from seizures that cause a loss of consciousness or cause abnormal movements.[31]

If on the other hand, the seizures occur in an area that is too vital to remove (such as areas that control motor, sensory or language functions), then the surgeon will perform a procedure known as a multiple subpial transection. This procedure involves making a series of cuts that surround the focal region where the seizures have originated.[32] By making cuts surrounding the focal region, the surgeon is able to isolate that specific section of the brain and prevent electrical impulses from being able to travel horizontally to other areas of the brain.

The last surgical procedure that can be done to help prevent the reoccurrence of seizures in the frontal lobes is to implant a stimulator on the vagus nerve. This device is a self-activating device that is inserted directly under the skin and can be controlled directly by the patient.[33] When a patient is feeling the onset of an aura, he/she can activate the stimulator which in turn will provide stimulation to the left vagus nerve (the left vagus nerve is used because the right nerve plays a role in cardiac function). Although little is understood about the exact mechanism for vagal nerve stimulation, it has been proven to be a successful treatment that can often terminate seizures before they begin.

Diet[edit]

The use of a regimented diet is an approach that has been found to help control seizures in children with severe, medically intractable frontal lobe epilepsy. Although the use of dieting to prevent seizures from occurring is a lost treatment that has been replaced by the use of new types of anticonvulsants, it is still recommended to patients to this day. A ketogenic diet is a high-fat, low-carbohydrate based diet that patients are typically asked to follow in conjunction with their anticonvulsant medications.[34] This diet was designed in order to mimic many of the effects that starvation has on the metabolic functioning of the body. By limiting the amount of carbohydrates and increasing the amount of exogenous fats available to the metabolism, the body will create an excess of water-soluble compounds known as ketone bodies.[34] Although the mechanism of action is still unknown, it is believed that these excessive amounts of ketone bodies become the brain's main source of energy and in turn are able to suppress the frequency of seizure occurrence.

Epidemiology[edit]

Epilepsy is a relatively common disorder, affecting between 0.5-1% of the population,[35] and frontal lobe epilepsy accounts for about 1-2% of all epilepsies.[3]The most common subdivision of epilepsy is symptomatic partial epilepsy, which causessimple partial seizures, and can be further divided into temporal and frontal lobe epilepsy. Although the exact number of cases of frontal lobe epilepsy is not currently known, it is known that FLE is the less common type of partial epilepsy, accounting for 20-30% of operative procedures involving intractable epilepsy.[36] The disorder also has no gender or age bias, affecting males and females of all ages. In a recent study, the mean subject age with frontal lobe epilepsy was 28.5 years old, and the average age of epilepsy onset for left frontal epilepsy was 9.3 years old whereas for right frontal epilepsy it was 11.1 years old.[1]

Research[edit]

Over the past decade or so, researchers have been attempting to discover less invasive, safer and more efficient technologies that enable surgeons to remove epileptogenic focal zones without causing any damage to neighboring cortical areas. One such technology that has emerged and has great promise, is the use of gamma knife radiosurgery to either excise a brain tumor or repair a vascular malformation.[37]

In Gamma Knife radiosurgery, intersecting gamma radiation beams are applied directly to the tumor site or vascular malformation site that had been established using neuroimaging.[37] Although each beam itself is not strong enough to damage brain tissue, when the beams interesect they are strong enough to destroy the specific brain tissue that is to be excised. This process is extremely efficient and entirely non-invasive and is therefore much safer than actual neurosurgery itself.

Recently researchers and surgeons alike have begun to use Gamma Knife radiosurgery to treat cases of epilepsy by removing tumors responsible for causing the seizures.[38][39] The early success rates in being able to alleviate seizures seem to be similar to those of temporal resective surgery however Gamma Knife radiosurgery has less associated risk factors.[39] Current research on this topic is aimed at improving the technique in order to increase success rates as well as developing non-invasive forms of physiologic monitoring in order to determine the epileptogenic focus conclusively.[39]

References[edit]

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External links[edit]