Glossary

Absence Seizure: Commonly seen in children between four years old and adolescence. There is no warning or postictal period. Patients have abrupt alteration of consciousness, with staring and a blank facial expression, usually lasting less than 15 seconds. Automatisms may occur. The electroencephalogram reveals generalized 3 Hertz spike and wave.

 Absence Status Epilepticus (Spike Wave Stupor): Rather than blink or stare as in an absence seizure, patients are confused. Absence status typically is seen in children, but may present in old age in patients who have never had seizures. There is a good response to intravenous diazepam.

 Agyria (Lissencephaly): A type of cortical dysplasia with inadequate cortical sulcation and gyration. The cortex is smooth and thin, with most of the cortical neurons misplaced in a subcortical layer.

 Aicardi Syndrome: This syndrome of mental retardation, infantile spasms, agenesis of the corpus callosum, and chorioretinal lacunae affects only females and has a high rate of early mortality. Vertebral body abnormalities are common. An intrauterine insult during gestation may be responsible.

 Artifact: Electroencephalogram (EEG) signals not related to brain waves. Muscle activity, sweat, patient movement, and poor electrode contacts are common sources of artifacts. Cardiac pacemakers, intravenous infusion pumps, and telephones also can create abnormal EEG signals. Artifacts can obscure important brain signals or may be mistaken for epileptic activity. Extensive training in EEG interpretation is essential to appropriately recognize artifacts.

 Astatic Seizure: A drop attack that may be due to a tonic, atonic, myoclonic, or partial onset seizure. Astatic seizures most often are seen in Lennox-Gastaut syndrome and may result in injury.

 Atonic Seizure: A seizure due to loss of muscle tone. The head may drop, or if postural tone is lost, the patient may fall to the ground in a "drop attack." Injury may occur, particularly to the face.

 Atypical Absence Seizure: Lasts longer than a typical absence seizure, more often has tone changes, associated with an abnormal interictal electroencephalogram (EEG) and seen in patients with mental retardation. The ictal EEG is faster or slower than the 3 Hertz spike and wave seen in a typical absence seizure.

 Aura: The characteristic warning that heralds a partial seizure. Actually, the aura represents focal epileptic activity and is the beginning of a seizure. Clinical symptomatology depends on the location of the epileptic discharge. For example, a mesial temporal lobe focus can elicit an aura of fear, an occipital lobe focus can cause flashing lights or spots, and a frontal lobe focus can result in contralateral motor movements.

Automatisms: Involuntary abnormal movements that occur during or after an epileptic seizure while consciousness is impaired. Patients may chew, smack their lips, swallow, rub their hands, or perform more complex movements such as walking or undressing. An automatism may be new motor activity or a continuation of preictal behavior.

Arteriovenous malformations (AVMs): A tangling of minute blood vessels in the brain in which the blood from the arteries abnormally flows into the veins. The Gamma Knife treats this tangling, often referred to as the "nidus."

 Benign Epileptiform Transients of Sleep: These small spikes can be unilateral or bilateral. Also known as small sharp spikes of sleep (SSS), these benign discharges should not be confused with epileptic spikes.

Benign Familial Neonatal Convulsions: Occur primarily on days 2 and 3 after birth, these clonic and apneic seizures are dominantly inherited. Only approximately 14 percent of these infants develop epilepsy.

 Benign Neonatal Convulsions: These clonic or apneic seizures occur without known cause on day 5 after birth ("fifth day fits"). The electroencephalogram may show alternating theta waves. Development is normal and seizures do not recur.

 Benign Myoclonic Epilepsy in Infancy: In this rare disorder, myoclonic seizures occur in normal children in the first or second year of life. Approximately one third have a family history of seizures. Developmental delay often occurs. Seizures respond well to medication. Convulsions may occur during adolescence.

 Benign Rolandic Epilepsy: Also known as benign epilepsy with centrotemporal spikes, the name refers to the large epileptic spikes seen on the electroencephalogram (EEG). Seizures begin between age 2 and 13 years and are characterized by speech arrest, salivation, and facial jerking. Hemiconvulsions and convulsions also may occur. Three quarters of the seizures occur during sleep. Neuroimaging and the neurologic examination between seizures are normal. The EEG may be positive only during sleep. Patients respond well to antiepileptic drugs, and some do not require medication. Benign rolandic epilepsy is age-related, and seizures disappear by age 16.  

Burst Suppression: This electroencephalographic pattern of bursts of high voltage slow waves mixed with sharp waves or spikes followed by periods of relative flatness is most commonly seen in the comatose patient and is associated with a poor prognosis.

CAT scan or CT (computerized tomography): A method of examining body tissues such as the brain using x-rays, with the beam passing or scanning through a body part and a computer measuring the density of the organ being examined. It compiles an image or picture by computer analysis. CT scans are excellent for identifying bone structures and to detect a hemorrhage.

Catamenial Epilepsy: Some women have seizures only at the time of menstruation. Many other women note an increase in seizures in the perimenstrual (days -3 to 3), ovulatory (days 10 to 13), or latter half of their menstrual cycle. Studies report a range of 10 percent to 78 percent of women with catamenial epilepsy, depending on the magnitude of seizure increase required by the authors. These patterns become evident when women carefully document seizure frequency and menstruation on a calendar. An increase in the estradiol:progesterone ratio may be responsible for the observed increase in seizures. Identifying a hormonal link to seizure frequency may allow for more targeted treatment.

Cerebral arteriography or angiography: A procedure that enables blood vessels to be seen on film after the vessels have been injected with a substance that is visible to x-rays. The resulting films are called angiograms or arteriograms. This imaging technique gives more precise information than MRI or CT scans.

 Childhood Absence Epilepsy (Petit mal, True petit mal, Pyknolepsy): Characterized by multiple staring spells, this seizure type occurs in preschool or school-aged children who otherwise are neurologically normal. Seizures may be provoked by hyperventilation. The electroencephalogram reveals generalized 3 Hertz spike and wave. Forty percent of patients also have generalized tonic-clonic seizures. Ethosuximide or valproate readily control staring spells. Children usually outgrow this syndrome, which is a type of primary generalized epilepsy (see Absence Seizure).

 Clonic Seizure: Repetitive jerking of muscles during a seizure.

Cobalt-60: The radioactive source (isotope) used in the Gamma Knife. Pellets of the isotope are enclosed in 201 small metal cylinders, which are mounted inside the Gamma Knife.

Collimator helmet: A half spherical, helmet-like device with small openings of different sizes through which the radiation passes into the brain during a Gamma Knife procedure. It is attached to the couch. The patient's skull is positioned in the helmet by the stereotactic head frame. There are four different helmets with different size portals (4, 8, 14 and 18 mm).

Comprehensive Epilepsy Program: Often found at a medical school, these programs combine the skills of an epileptologist, neurosurgeon, neuropsychiatrist, neuropsychologist, neuroradiologist, social worker, nurse clinician, and others in a dedicated team designed to help patients with epilepsy. A comprehensive epilepsy center can provide advanced neurodiagnostic studies such as magnetic resonance imaging (MRI), single photon emission computed tomography (SPECT), positron emission tomography (PET), and video-EEG monitoring. Investigational AEDs and other research protocols will also be available. Patients likely to benefit from a comprehensive epilepsy program are those with anatomic lesions referred for epilepsy surgery, persistent seizures despite treatment with multiple AEDs, or suspected nonepileptic seizures.

 Computerized Axial Tomography: A CAT or CT scan. Multiple x-ray images taken in different planes by a movable gantry are reconstructed to provide cross-sectional views of the skull and brain. CAT scans are particularly useful when searching for calcium, blood, or skull defects.

 Convulsion: A generalized tonic-clonic seizure. A partial seizure may spread to become a convulsion, or a convulsion may begin globally without a focal onset.

Corpus Callosotomy: A type of epilepsy surgery particularly used for patients who have "drop attacks" due to atonic seizures and are at risk for injury. Many of these patients have Lennox-Gastaut syndrome. When the corpus callosum is severed, epileptic discharges can no longer spread as easily from one hemisphere to the other. This surgery can greatly reduce drop attacks, but it does not improve partial seizures.

 Cortical Dysplasia: Broad category of neuronal migration disorders. Examples include microdysgenesis, agyria, pachygyria, polymicrogyria, and laminar heterotopia. These developmental abnormalities often lead to childhood epilepsy.

CT or CAT scan (computerized tomography): A method of examining body tissues such as the brain using x-rays, with the beam passing or scanning through a body part and a computer measuring the density of the organ being examined. It compiles an image or picture by computer analysis. CT scans are excellent for identifying bone structures and to detect a hemorrhage.

Cytochrome P450: A hepatic enzyme system consisting of more than a dozen isoenzymes responsible for the metabolism of most AEDs. For example, cytochrome P450 3A4 metabolizes carbamazepine, while phenytoin is metabolized by cytochrome P450 2C8/9/10. Cytochrome P450 activity may be induced or inhibited by AEDs and many other drugs, affecting the rate of AED metabolism and resultant serum AED levels. The potential effect on the cytochrome P450 system should be assessed whenever a new drug is added to a patient's regimen.

 Déjà Vu: A sensation that a new experience has occurred before. Déjà vu is a disturbance of higher cerebral function characteristically due to a partial seizure localized in the temporal lobe. A déjà vu sensation may occur as an aura prior to a complex partial or generalized seizure.

 Depth Electrodes: Invasive electrodes used to determine the seizure focus when scalp electroencephalograms remain inconclusive. Typically, four to six electrodes are placed stereotactically into the brain under computed axial tomography or magnetic resonance imaging guidance through small holes drilled into the skull. These electrodes are associated with a small risk of hemorrhage and infection.

Digital subtraction angiography (DSA): See cerebral arteriography or angiography.

 DigiTrace: An ambulatory electroencephalogram (EEG) monitoring system that uses digital technology. The patient has EEG electrodes connected to the scalp and then takes the DigiTrace computer home for one to several days. The device contains computer software that records background samples, spikes, electrographic seizures, and push-button events. These are later downloaded and reviewed on paper. DigiTrace can also be used with video.

 Early Myoclonic Encephalopathy: Myoclonus, partial seizures, or tonic spasms begin before 3 months of age. Early myoclonic encephalopathy occurs frequently in families. The electroencephalogram reveals suppression-burst activity. This severe seizure disorder may result in death before the age of 1 year.

 Electroencephalogram: First discovered by Hans Berger in 1929, the electroencephalogram (EEG) remains an essential component of all clinical neurophysiology laboratories. Human brain waves reveal levels of mental alertness, sleep stages, and the presence or absence of epileptic activity. Scalp electrodes distributed in an array over the head detect endogenous cerebral electricity, which is then filtered, amplified, and continuously recorded on paper by voltage sensitive pens. Typically, 16 channels of electrical activity from different brain areas are displayed. A standard EEG represents 20 minutes of continuous recording. Modern digital EEG machines can display brain waves on a computer screen or laser printout. Prolonged recordings can save hours or days of collected information to a computer hard drive. To enhance review, software can search the record for spikes and subclinical seizures.

Electrographic Seizures (Subclinical Seizures): Seizures detected on the electroencephalogram that do not produce clinical symptoms.

 Epilepsia Partialis Continua: Focal motor seizures, usually of the face or arms, consisting of clonic movements which continue for hours or days. Consciousness is preserved. Postictal weakness occurs. Rasmussen's encephalitis is commonly responsible, but these enduring seizures may also be caused by Alper's disease, subacute type of delayed measles encephalitis, and mitochondrial encephalomyopathy with lactic acidosis and strokelike episodes.  

Epilepsy with Continuous Spikes and Waves During Slow Sleep: Spike wave activity occurs during at least 85 percent of slow wave sleep. Convulsions, absences, and myoclonic seizures can occur. Behavior and speech deteriorate. Seizures disappear by puberty but mental sequelae may remain.

Epilepsy with Grand Mal Seizures on Awakening: Average age of onset is 17 years. Nearly all convulsions occur after awakening from sleep, whether in the morning or after a nap. Absence or myoclonic seizures may also be seen. This appears to be an idiopathic generalized epilepsy with genetic predisposition. Seizures respond well to antiepileptic medication but often recur when drugs are stopped.  

Epilepsy with Myoclonic Absences: Absence seizures begin at a mean age of 7 years accompanied by severe clonic jerks, often with a tonic contraction. Seizures are frequent and do not respond well to therapy. Mental deterioration may occur.

Epilepsy with Myoclonic-Astatic Seizures: Absence with clonic and tonic components, astatic, myoclonic, myoclonic-astatic, and tonic-clonic seizures can occur in this childhood syndrome. Status epilepticus is frequent.

Epileptic Syndrome: A constellation of symptoms and signs, seizure types, etiology, anatomy, age of onset, precipitating factors, and other characteristics. Defining an epilepsy syndrome guides treatment and refines prognosis. Examples of epilepsy syndromes are Lennox-Gastaut, benign rolandic epilepsy, childhood absence epilepsy, juvenile myoclonic epilepsy, and West Syndrome.

Epileptic Twilight State: See Absence Status Epilepticus.

Febrile Seizures: Seizures that occur in 3 percent to 5 percent of children between the ages of 6 months and 5 years with fever not related to central nervous system (CNS) infection. Most occur during bacterial or viral infections between 18 and 24 months of age. Very few of these children develop epilepsy.

Febrile seizures can be divided into "simple" and "complex." (These adjectives have different meanings here than when applied to partial seizures!) Most children have "simple" febrile seizures. These convulsions last less than 15 minutes, lack focality, and do not recur within 24 hours. Febrile seizures become "complex" when they exhibit one or more of the following features; last longer than 15 minutes, focal motor movements, a neurologic deficit, recur during the same day, or there is a parent or sibling with epilepsy. This differentiation is clinically useful because children with two or more "complex" features have a 6 percent risk of developing epilepsy by age 7, whereas children with simple febrile seizures have a less than 1 percent risk. In addition, children with complex febrile seizures need to be evaluated more aggressively for CNS infection or intracranial lesion. Children with one or two simple febrile seizures do not require chronic antiepileptic drug therapy. These seizures appear to be a benign response to fever that is age related and later outgrown. Complex febrile seizures are more likely to require ongoing antiepileptic treatment. Oral or rectal benzodiazepines may be useful for children with recurrent febrile seizures.  

Fugue State (Poriomania): A prolonged period of aimless wandering with amnesia. Fugue states probably more often represent psychogenic dissociative disorders rather than postictal states.  

Gamma radiation: Similar to x-ray (photon radiation) but much more powerful. It is not a laser. Gamma radiation is invisible, cannot be felt and is able to penetrate deep through tissues. The radioactive source is Cobalt-60.

Geschwind Syndrome: A cluster of personality traits thought overrepresented in patients with temporal lobe epilepsy, particularly hypergraphia, hyper-religiosity, and hyposexuality. Other personality traits associated with temporal lobe epilepsy are; emotionality, manic tendencies, depression, humorlessness, anger, aggression, nascent philosophical interest, augmented sense of personal destiny, dependence, paranoia, moralism, guilt, obsessionalism, circumstantiality, and viscosity. (The prevalence of the Geschwind syndrome is still much debated.)

 Grand Mal Seizures: Loosely translates from the French to "big bad" seizures. These are generalized tonic-clonic seizures or convulsions.

 Grid: An array of electrodes placed on the surface of the brain to determine seizure onset or used to map cortical function such as speech.

 Half-life: The time it takes for the serum concentration of an antiepileptic drug to decrease by 50 percent. Half-lives vary from as short as 5 hours for gabapentin to as long as 136 hours for phenobarbital. Metabolic rate affects serum half-lives. Consequently, hepatic induction will decrease the half-life of most AEDs, while decreased hepatic and renal function increase AED half-lives. (Half-lives tend to be increased in the elderly.)

When an AED with linear kinetics, such as phenobarbital, is discontinued, the serum level will decrease by 95 percent after five half-lives. Similarly, it takes five half-lives to reach a steady state when beginning a new AED. (Most AEDs exhibit linear kinetics, except for carbamazepine, phenytoin, and lamotrigine.)

 Hemimegalencephaly: The affected side of the brain has a larger hemisphere and ventricle. The cortex is excessively thick with abnormal neuronal architecture. Giant neurons occur and calcifications may be seen in this rare developmental cerebral malformation.

 Hemispherectomy: A type of epilepsy surgery reserved for patients with intractable epilepsy due to a globally dysfunctional hemisphere. Many of these patients already have a congenital hemiplegia opposite the affected hemisphere. During surgery, dysfunctional cortex is disconnected from the white matter and partially removed. In addition to excellent seizure control after this operation, many of these patients paradoxically have improvement in cognitive function.

 Hertz: A unit of frequency (cycles per second) named after Heinrich Hertz, the discoverer of radio waves.

 Heterotopia: A cluster of neurons in an abnormal location resulting from abnormal neuronal migration between the second and fifth months of gestation. Three major types of neuronal heterotopia are focal subcortical heterotopia, periventricular nodular heterotopia, and subcortical band heterotopia (double cortex syndrome). These misplaced neurons can be the source of epileptic seizures.

 Hippocampal Sclerosis: Neuron loss and gliosis of the hippocampus associated with temporal lobe epilepsy. First described by Sommer in 1880, this distinctive pattern of cell loss can appear on magnetic resonance imaging as hippocampal atrophy and signal change.

Hyperekplexia (Startle Disease): An autosomal dominant movement disorder characterized by sudden loss of postural control related to a startle stimulus. Patients also may have spontaneous clonus. Symptoms may be confused with those of epilepsy. 

Hypsarrhythmia: A dramatic pattern on the electroencephalogram in patients with infantile spasms. High voltage irregular slow waves, sharp waves, and multifocal epileptic spikes occur. Fast activity and burst suppression may also be seen.

 Ictal: The period of clinical and electrical epileptic activity.

 Impulsive Petit Mal (Juvenile Myoclonic Epilepsy of Janz): A primary generalized epilepsy with onset at age 12-18 years. Patients have myoclonic seizures, particularly when fatigued. These can occur in clusters and lead to convulsions. Absence seizures occur in up to a third of these patients. Response to valproate is excellent, but patients rarely outgrow this syndrome. Continued treatment is required.

 Infantile Spasms: The first clinical description of infantile spasms appeared in the Lancet in 1841, provided by West describing these unusual seizures in his own son. Eighty-five percent of cases occur in infants before 12 months of age. Infantile spasms have a mortality of 10 percent to 20 percent and a morbidity of 75 percent to 90 percent. Approximately 25 percent of cases of infantile spasms evolve to Lennox-Gastaut syndrome. The best prognosis is seen in children who are normal when seizures begin and in whom no cause can be found for the spasms.

Seizures consist of flexor and/or extensor spasms of the body, which tend to occur in clusters. Infantile spasms are part of the triad of West's syndrome, which includes a hypsarrhythmic electroencephalogram and mental retardation. Up to 25 percent of cases of infantile spasms are associated with tuberous sclerosis.

 Interictal: Refers to the time between seizures when patients are at their baseline.

 Interictal Dysphoric Disorder: A recently described epilepsy specific affective disorder, with an intermittent and pleomorphic symptom profile. Patients exhibit three to eight of the following symptoms in the interictal period: depressive mood, anergia, pain, insomnia, fear, anxiety, paroxysmal irritability, and euphoric moods. Symptoms tend to be of sudden onset and brief duration. The most common are depressive mood, anergia, and irritability. Patients with temporal lobe epilepsy are at highest risk for interictal dysphoric syndrome.

 Intractable Epilepsy: Seizures that persist despite appropriate treatment. Approximately 20 percent to 40 percent of patients have seizures that do not respond to adequate doses of appropriate antiepileptic drugs (AEDs). Usually, several AEDs are tried over a period of years before a patient is considered intractable. Patients with intractable epilepsy are potential candidates for investigational drug trials, epilepsy surgery, and novel treatments such as the vagal nerve stimulator.

 Jamais Vu: A distortion of memory producing a feeling that a familiar experience has never occurred before (opposite of déjà vu.) Jamais vu and déjà vu are types of psychic auras and represent partial seizures.

 Juvenile Absence Epilepsy: A primary generalized epilepsy occurring around puberty with absence seizures. Convulsions occur in approximately 50 percent of patients. Patients respond well to medication.

Juvenile Myoclonic Epilepsy of Janz: See Impulsive Petit Mal.

K complex: A normal feature of sleep architecture that appears in stage 2 of sleep. Sharp, slow, and fast components make up the K complex.

Kearns-Sayre Syndrome: A mitochondrial encephalomyopathy that occurs in children and is characterized by ophthalmoplegia and pigmentary retinopathy. Patients also may have ataxia, cardiac conduction block, elevated cerebrospinal fluid protein, and dementia. Unlike patients with myoclonic epilepsy and ragged red fibers or mitochondrial encephalomyopathy with lactic acidosis and strokelike episodes, only a few patients with Kearns-Sayre syndrome experience seizures.

Ketogenic Diet: Pioneered in the beginning of the 20th century, the ketogenic diet requires a high ratio of fat to carbohydrate and protein—typically 3:1 or 4:1—that produces systemic ketosis. Fluid also is restricted. Improvement in seizure control can occur when the diet is rigorously followed. The exact mechanism of action that promotes seizure control is not known.

Compliance may be a problem because of the strictness of the diet, care needed in meal preparation, and side effects of hunger and constipation. Nonetheless, the ketogenic diet is a reasonable treatment alternative for properly motivated patients and caregivers. In a Johns Hopkins study of 58 patients with mental retardation, cerebral palsy, and mixed seizure types, 29 percent became seizure-free and 38 percent had a better than 50 percent improvement. One third were not helped. In addition, 10 percent of the children discontinued their antiepileptic drugs.

 Laminar Heterotopia: A neuronal migration disorder, also known as band heterotopia or double cortex syndrome. The sulcal pattern is normal, but an abnormal zone of gray matter is bordered on both sides by white matter. Appears restricted to females (see Heterotopia).  

Landau-Kleffner Syndrome: A childhood syndrome of unknown etiology, consisting of progressive receptive and expressive aphasia, and an epileptiform electroencephalogram (EEG). Seventy percent of patients exhibit clinical seizures, most commonly partial complex. Epileptic activity is frequent on the EEG and tends to be more pronounced during sleep. Severe behavior problems commonly occur. Outcome is variable, with some children making a complete recovery as adults.

Lennox-Gastaut Syndrome: A childhood epileptic syndrome of intractable epilepsy, mental retardation, and slow spike and wave on the electroencephalogram. Multiple seizure types occur, particularly atypical absence, tonic, and atonic seizures. Myoclonic, partial and generalized tonic-clonic seizures also may be seen. Seizures are extremely difficult to control. Felbamate, lamotrigine, topiramate, valproate, and the benzodiazepines can reduce seizures. Oversedation with multiple medications is a frequent problem. The ketogenic diet may be helpful in reducing seizures. Lennox-Gastaut syndrome begins at ages 1-6 years and may evolve from West syndrome. In addition to the seizures, most of these children have other neurologic abnormalities. The prognosis is poor.

Lissencephaly: See Agyria.  

Mental Retardation: Decreased intellectual functioning with an IQ less than 70, affecting language, visual, motor, and social abilities. One third of patients with severe mental retardation requiring institutionalization also have epilepsy.

Mesial Temporal Sclerosis: A specific pattern of neuronal cell loss, gliosis, and neuronal reorganization in the medial temporal lobe commonly responsible for partial complex seizures. The hippocampal atrophy of mesial temporal sclerosis can often be detected by magnetic resonance imaging. Many patients give a history of febrile seizures. Patients with intractable epilepsy due to mesial temporal sclerosis can be cured by temporal lobectomy 80 percent to 90 percent of the time.

 

Mitochondrial Encephalomyopathy with Lactic Acidosis and Strokelike Episodes: A maternally inherited syndrome characterized by normal early development, recurrent headaches, and vomiting. Patients suffer strokelike episodes and almost always have seizures. Ataxia, dementia, exercise intolerance, muscle weakness, myoclonus, sensorineural hearing loss, and short stature may be present. (Patients may resemble those with myoclonic epilepsy and ragged-red fibers.)

 Monotherapy: The treatment of epilepsy with a single medication rather than a combination. Monotherapy has distinct advantages over polytherapy in many patients, including absence of drug-drug interactions, fewer side effects, simpler dosing, and lower cost. However, not all patients can be controlled with monotherapy.

Magnetic resonance imaging (MRI): A scanning technique that uses a very powerful magnet to record, process and analyze the radio waves generated by body tissues during the exam. The result is a computergenerated image of the area scanned. MRI is excellent for scanning soft tissue structures. Contrast (gadolinium) is usually injected to make tumors show up better.
More about MRI

 Myoclonic Epilepsy with Ragged-Red Fibers: Previously described by Ramsey Hunt as dyssynergia cerebellaris myoclonica, myoclonic epilepsy with ragged-red fibers (MERRF) is the first hereditary epilepsy syndrome to be characterized by a specific mitochondrial mutation. MERRF is a maternally inherited syndrome characterized by ataxia, myoclonus, and seizures. Patients may also have deafness, dementia, lactic acidosis, lipomas, peripheral neuropathy, and short stature. Muscle biopsy reveals ragged red fibers, which are related to subsarcolemmal mitochondrial accumulations in muscle fibers. All patients with MERRF have seizures.

 Myoclonus: Brief motor jerks that may represent epileptic seizures or nonepileptic etiologies. A history of myoclonus can help point to a specific epilepsy syndrome, such as myoclonic epilepsy of Janz.  

Neuronal Migration Disorders: Cerebral malformations such as focal cortical dysplasia, polymicrogyria, and the nodular heterotopias occur when migrating neurons do not reach their appropriate cortical destinations. Genetic factors and a variety of intrauterine insults such as drugs, infections, radiation, and/or toxins may be responsible.

 Nonconvulsive Status Epilepticus: A prolonged seizure state characterized by mental slowness, confusion, or even stupor or coma. Nonconvulsive status epilepticus may be due to either persistent absence seizures or partial complex seizures. An electroencephalogram will be necessary to confirm this diagnosis.

 Nonepileptic Seizures (Pseudoseizures, Psychogenic Seizures): These may be physiologic events such as syncope, tics, or transient ischemic attacks that are mistaken as epileptic seizures. More commonly, staring spells, abnormal movements, or convulsions result from psychiatric problems such as conversion disorder, malingering, or panic attacks. The diagnosis of recurrent unexplained spells can be very difficult to make with only the patient as witness. Consequently, video-EEG may be required in order to diagnose nonepileptic seizures.

 Pachygryria: A type of cortical dysplasia with wide cortical convolutions and heterotopic neurons.

 Partial Seizure: A seizure that begins in a specific cortical location, or focus. An anatomic abnormality, such as a brain tumor or an arteriovenous malformation, or an electrical lesion that can only be seen by electroencephalography may be responsible. Partial seizures are divided into "simple" and "complex" seizures. Consciousness is preserved in partial simple seizures but altered in partial complex seizures. Partial seizures are the most common seizure type in adults.

Partial Complex Seizure: A partial complex seizure begins in a specific location, such as the temporal or frontal lobe, and causes alteration of consciousness. Temporal lobe partial complex seizures are sometimes called psychomotor seizures. Typically, these last from 30 seconds to several minutes. Automatisms, such as lip smacking, chewing, swallowing, and fumbling with clothes, commonly occur. Because of the alteration of consciousness, patients may not always be aware they have had a seizure. This limits their ability to self-report seizure frequency and underlines the importance of a witness or caretaker to assist in medical management.

Partial Simple Seizure: A partial simple seizure begins in a specific brain location and does not cause alteration of consciousness. For example, a seizure that begins in the frontal lobe and causes motor movements of the opposite extremity is a partial simple seizure. An epileptic aura, such as a smell, visual hallucination, or sound, is also a partial simple seizure. Partial simple seizures may be self-limited or evolve into partial complex or secondarily generalized seizures.

 Petit Mal Seizure: See Childhood Absence Epilepsy.

Petit Mal Variant: A slow spike and wave pattern seen on the electroencephalogram at 1-2.5 Hertz. This pattern differs from the three Hertz pattern seen in classic "petit mal" absence seizures. Petit mal variant is seen in Lennox-Gastaut syndrome, a severe type of childhood epilepsy.

 Pharmacodynamic Interactions: The physiologic consequence of combining drugs with similar mechanisms of action. The results may be additive, more than additive, or antagonistic.

 Pharmacokinetic Interactions: One drug can alter serum concentrations of another. Several types of pharmacokinetic interactions occur, including effects on drug distribution, metabolism, and excretion. Enzyme inhibition or induction by one drug often affects the half-life of another. For example, valproate extends the half-life of lamotrigine, whereas carbamazepine decreases the half-life of topiramate. Pharmacokinetic interactions can be assessed directly by measuring antiepileptic drug levels.  

Polycystic Ovary Syndrome: Characterized by polycystic ovaries, hirsutism, acne, obesity, elevated androgens, an elevated luteinizing hormone (LH):follicle stimulating hormone (FSH) ratio, chronic anovulation, and insulin resistance. Polycystic ovary syndrome is increased in women with temporal lobe epilepsy fourfold over that of women in the general population. In addition, women taking sodium valproate have been found to have an increase in polycystic ovary syndrome, but the relationship to the drug remains under investigation.

Polymicrogyria: A cortical abnormality with excessive numbers of small gyri. Polymicrogyria can be focal or diffuse. Intrauterine cytomegalovirus infection can cause polymicrogyria. Ischemia may also be responsible. Congenital bilateral perisylvian syndrome due to polymicrogyria consists of developmental delay, pseudobulbar paresis, and typical imaging findings. Most patients have seizures.

 Polypharmacology: Multiple actions of a single drug. For example, topiramate limits sustained repetitive firing via state-dependent blockade of sodium channels, potentiates GABA-mediated neuroinhibition at GABA (A) sites, blocks glutamate-mediated neuroexcitation, and is a carbonic anhydrase inhibitor.  

Polytherapy: The treatment of epilepsy with medication combinations. Because not all patients can be controlled with monotherapy, sometimes two or more medications are effective. Whenever possible, drugs with complementary mechanisms of action and different side-effect profiles should be used. For example, phenytoin and valproate represent a logical combination, whereas phenobarbital and primidone would offer more additive side effects than therapeutic advantages.

 Poriomania: See Fugue State.

 Positron Emission Tomography: A computerized imaging technique that allows imaging of cerebral metabolic rates, receptor densities, and blood flow. Most commonly, radioactive labeled F-fluoro-2-deoxyglucose assesses cerebral glucose metabolism. During the interictal period, positron emission tomography (PET) scans often identify regions of cerebral hypometabolism that correlate with the epileptogenic zone. During a seizure, this same region becomes hypermetabolic. PET may reveal abnormal brain regions not seen on magnetic resonance imaging.

 Postictal Psychosis: Psychosis in epilepsy can occur in the interictal, ictal, and postictal state. Although interictal psychosis is the most frequent type of psychosis, postictal psychosis comprises 25 percent of the psychoses in this population. Postictal psychosis usually occurs after a cluster of convulsions. A lucid interval lasting 1 to 6 days frequently precedes the psychosis. Most patients exhibit abnormal mood and paranoid delusions. Psychotic episodes last days to weeks. Neuroleptic treatment may not be required. Postictal psychosis may be related to increased dopamine release.

 Prolactin: A hormone produced by the anterior pituitary gland. Serum prolactin levels often increase 3 to 20 times baseline after a seizure. Prolactin levels peak 10 to 20 minutes after a seizure and return to baseline in an hour. Prolactin levels are used along with the electroencephalogram to help differentiate epileptic seizures from nonepileptic spells. Because prolactin levels vary during the day, a repeat serum prolactin level 24 hours later is needed for comparison. Prolactin elevations occur in 90 percent of tonic-clonic seizures, approximately 70 percent of partial complex seizures, and 10 percent of partial simple seizures. Consequently, the absence of a prolactin rise is less helpful than a definite increase. Prolactin usually does not increase in frontal lobe partial complex seizures. Prolactin elevations also can occur from many other sources, including pregnancy, prolactinomas, general anesthesia, phenothiazines, butyrophenones, and metoclopramide.

 Pseudoseizures: See Nonepileptic Seizures.

 Psychomotor Variant: An electroencephalographic pattern, composed of rhythmic bursts of theta waves, that resembles an epileptic discharge. Most often seen in drowsiness, this normal variant is also known as "rhythmic midtemporal discharges" or "rhythmic temporal theta bursts."

 Psychomotor Epilepsy: A historical term referring to the varied psychic phenomena that occur during certain types of seizures. The vast majority of seizures of this type originate in the temporal lobe. Seizures beginning in the temporal lobe may cause autonomic, dysmnesic, emotional, gustatory, olfactory, visual, and other strange symptoms.

Radioactive source: The source that emits the radiation (gamma radiation in this case) by the process of radiation decay. Cobalt-60 is the radioactive source used in the Gamma Knife.

 Radioligand: A radioactive pharmaceutical tracer used in positron emission tomography or single photon emission computed tomography. Radioligands can be fabricated to evaluate glucose or oxygen utilization, cerebral blood flow, benzodiazepine, cholinergic, or opiate receptor distribution, and other aspects of the central nervous system.

 Rasmussen's Encephalitis: Usually presenting in children, Rasmussen's encephalitis is characterized by progressive hemiplegia, mental decline, and intractable seizures. About 50 percent of patients manifest epilepsia partialis continua. Brain biopsy reveals cortical inflammation with gliosis and tissue destruction. Traditional treatment has been functional hemispherectomy. The benefits of plasma exchange and immunosuppressant treatment are under evaluation for this probable autoimmune disorder.  

Schizencephaly: A developmental abnormality resulting in a cleft extending from the pial cerebral surface to the ependymal surface of the ventricle. Dysplastic gray matter often lines the cleft. Heterotopias may be present. Patients with schizencephaly may have severe developmental delay, microcephaly, and seizures.

 Sharp Wave: A sharply contoured wave on the EEG too prolonged to meet spike criteria, but may suggest epileptic activity. Sharp waves last between 70 and 200 milliseconds.

Single Photon Emission Computed Tomography: Noninvasive nuclear medicine imaging of cerebral blood flow used at epilepsy centers to help determine the lateralization and localization of a seizure focus. When the radioligand is injected at the onset of a seizure, single photon emission computed tomography (SPECT) scans can reveal cerebral hyperperfusion at the seizure focus. In between seizures (interictally), this same region may be hypoperfused. Ictal SPECT reliably identifies the seizure focus in temporal lobe epilepsy more than 90 percent of the time. Ictal SPECT can also provide useful localization information in extratemporal epilepsy.

Whereas traditional positron emission tomography (PET) measures cerebral glucose metabolism, SPECT measures cerebral blood flow. Both tests are complementary in the presurgical evaluation of the intractable epilepsy patient.

Spike: A specific electroencephalogram abnormality associated with epileptic seizures. A spike must last 20-70 milliseconds, display a pointed peak, and be distinct from the background.

 Spike Wave Stupor: See Absence Status Epilepticus.

 Startle Disease: See Hyperekplexia.

 Status Epilepticus: Recurrent or persistent seizures that create a fixed and lasting epileptic condition. Status epilepticus requires immediate evaluation for its underlying cause and simultaneous treatment of the seizures. Status epilepticus can be life-threatening, with mortality ranging from 1 percent to 10 percent. Any seizure or cluster of seizures without recovery that lasts 30 minutes or more qualifies as status epilepticus. (Therapeutic intervention should be attempted long before, however.)

Stereotactic head frame: An aluminum frame that is secured to the patient's head after the patient receives local anesthesia. It is used to define the target location and secure the head in the Gamma Knife's collimator helmet.

Stereotactic radiosurgery: The highly precise delivery of a single, high dose of radiation to a small area in the brain. This is achieved by letting a large number of beams all focus simultaneously at this area. Gamma Knife is one type of stereotactic radiosurgery and was the first to be used in clinical applications.

Stevens-Johnson Syndrome: Click for link

 Strip: A single row of electrical contacts used for monitoring electrical brain activity directly from the cortex. Strips can be placed through a burr hole or after craniotomy.

 Sturge-Weber Syndrome (Encephalofacial Angiomatosis): A neurocutaneous syndrome of uncertain inheritance. The constellation of facial nevus, mental retardation, contralateral hemiparesis, and glaucoma characterizes this syndrome. More than 70 percent of patients develop epilepsy, typically beginning in childhood. Status epilepticus often occurs. Patients have leptomeningeal angiomatosis and develop intracranial calcifications. Seizures may be refractory to antiepileptic drug therapy, although some patients dramatically improve with surgical resection.

 Subacute Sclerosing Panencephalitis: A rare progressive encephalopathy resulting from exposure to measles. Intellectual deterioration, personality changes, and intractable myoclonus occur. A characteristic suppression-burst pattern occurs on the EEG in 80 percent of patients.

Subclinical Seizures (Electrographic Seizures): These seizures are visible on the EEG, but the patient does not exhibit clinical symptoms. Electroencephalography often detects subclinical seizures during sleep.

Subclinical Rhythmic Electrographic Discharge of Adults: Rhythmic slowing of the temporo-parieto-occipital junction seen in some adults, which may be associated with aging or cerebrovascular disease. Rhythmic, subclinical rhythmic electrographic discharge of adults (SREDA) does not indicate seizure activity and is a normal variant.

 Subdural Electrodes: These electrodes are small metal contacts imbedded in silastic in different configurations, either strips or grids (see Grids). They are placed on the cerebral cortex to record electrical activity and assist in the localization of the seizure focus. Subdural electrodes can also be used as stimulation contacts in speech or other brain mapping.

Temporal Lobectomy: A surgical procedure pioneered by neurosurgeon Dr. Wilder Penfield for the cure of epilepsy related to temporal lobe seizures. Patients with mesial temporal sclerosis respond exceptionally well to temporal lobectomy.

 Therapeutic Range: Measured serum concentrations of antiepileptic drugs within which most patients have good antiepileptic effect with minimal toxicity. For example, the therapeutic range of carbamazepine is 4-12 µg/ml, phenytoin 10-20 µg/ml, and valproate 50-150 µg/ml.

Note, however, that many patients have good medication results with serum levels lower or higher than the published therapeutic range, while some patients experience toxicity within that range. Consequently, these measurements provide a guideline for treatment and constitute only one component of the clinical picture. Doses should not be changed merely because of a serum level lower or higher than the therapeutic range.

In addition, serum levels vary depending on the timing of the sample relative to the last dose, particularly for AEDs with shorter half-lives.

Reasons to measure serum AED levels include:

1. A new AED has been added

2. Patient appears toxic

3. Uncontrolled seizures

4. Compliance is suspect

 

Tonic: Stiffening of flexor or extensor muscles during a seizure. May occur as a tonic seizure or part of a tonic-clonic seizure. Tuberous Sclerosis: Accounts for 25 percent of cases of infantile spasms. Half of all patients with tuberous sclerosis (TS) and seizures present with infantile spasms. The prevalence of epilepsy in TS has been measured at greater than 80 percent.

Inheritance is autosomal dominant, giving a 50 percent chance of inheritance to the child of one affected parent. Parents may be so mildly affected that they are unaware of the disease. I have seen a number of adults with mild seizure disorders who did not know they had tuberous sclerosis. The diagnosis is essential for genetic counseling. Children may be more severely affected than their parents. In addition, TS occurs by spontaneous mutation 60 percent of the time.

Learning disability is common and, when severe, is usually accompanied by seizures. Clinical features of the syndrome are achromic nevi, adenoma sebaceum, subungual fibromas, shagreen patches, cardiac rhabdomyomas, renal tumors, and retinal phacomas. Cortical tubers, calcified hamartomas, and rare intraventricular giant cell astrocytomas occur. Patients should have cardiac and renal ultrasounds and an ophthalmologic exam to screen for extraneurologic manifestations.

 Uncinate Fits: Partial seizures from the anterior mesial temporal lobe or orbital frontal structures characterized by olfactory symptoms. Typically, the abnormal smell is unpleasant, often described as "burnt rubber." These seizures have traditionally been associated with neoplasms.  

Vagal Nerve Stimulator (Neurocybernetic Prosthesis): The first implantable device approved by the U.S. Food and Drug Administration for seizure control. A battery powered programmable generator, similar to a cardiac pacemaker, sends repeated stimulation via an electrode attached to the left vagus nerve. Many patients experience significant seizure reduction.  

Version: The turning of the head and eyes during a seizure. Sustained versive movements usually indicate a contralateral seizure focus from the frontal, temporal, or occipital lobes.  

Vertex Sharp Wave: A normal feature of drowsiness and light sleep. Vertex sharp waves should not be confused with epileptic spikes.

 Wada: Also known as intracarotid Amytal procedure. Pioneered by Juhn Wada, this test evaluates memory and laterality of language before temporal lobectomy. A carotid angiogram is performed, followed by an anesthetic injection. While one hemisphere is anesthetized, the other is assessed for memory and language function. After the patient recovers, the procedure is repeated on the other hemisphere.

Surgical candidates must demonstrate sufficient memory ability in the temporal lobe that will remain after surgery. Identification of language laterality allows the neurosurgeon to tailor the operation of the temporal cortex to protect language function.

West Syndrome: A triad of infantile spasms, mental retardation, and a hypsarrhythmic electroencephalogram. Most cases occur between the ages of 3 and 7 months, with prevalence of 0.3 per 1,000. Treatment of the seizures is with ACTH or antiepileptics such as valproate and the benzodiazepines. Felbamate, lamotrigine, topiramate, and vigabatrin can also help control infantile spasms. Only about 5 percent of patients have a normal outcome.

 Adapted from: Wilner, Andrew N. Epilepsy in Clinical Practice: A Case Study Approach. New York: Demos Medical Publishing, 2000.