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The EEG and epilepsy
When evaluating a new patient, the first line of inquiry for the clinician is, “is this a seizure?” There are many seizure mimics including parasomnias, syncope, transient ischemic attacks and psychogenic non-epileptic attacks (PNEA). A seizure is defined by the International League against Epilepsy (ILAE) to be “a transient occurrence of signs and/or symptoms due to abnormal excessive or synchronous neuronal activity in the brain.” If the event in question is a seizure, the next line of inquiry is: Is the onset of the seizure generalized or focal? According to the ILAE generalized epileptic seizures begin at “some point within and rapidly engaging, bilaterally distributed networks. Such bilateral networks can include cortical and subcortical structures, but not necessarily include the entire cortex. Generalized seizures can be asymmetric.” Focal epileptic seizures begin “within networks limited to one hemisphere. They may be discretely localized or more widely distributed.” In some cases, there can be more than one seizure focus, which makes the epilepsy multifocal. Focal seizures can spread and involve both hemispheres, hence the type of epilepsy pertains to the onset and not the propagation pattern. The electrographic representation of a seizure is often similar between individuals (e.g., temporal lobe seizures from hippocampal sclerosis or an absence seizure). Electrographic seizures always disrupt the background, they generally evolve from faster frequencies to slower frequencies, and the shape of the waves (morphology) often changes over the course of the seizure, most commonly becoming higher in amplitude. Multiple seizures from the same focus in the same individual will often have a very similar pattern. Table 5-1 delineates different seizure types and the EEG patterns associated with each seizure type.
Table 5-1
Seizure types and associated EEG patterns
| Clinical characteristics | EEG findings during the seizure | |
|---|---|---|
| Generalized seizures | ||
| Generalized tonic-clonic (GTC) | During the tonic phase, there is loss of consciousness and full body stiffening, often accompanied by a loud cry. In the clonic phase there is active rhythmic jerking. | Generalized fast activity (>10 Hz) that increases in amplitude and decreases in frequency during the tonic phase, with slow waves during the clonic phase ( Figure 5-1 ). |
| Absence seizures | ||
| Typical absence | Impairment of awareness for several seconds without loss of body tone. Sudden onset and cessation. Can have eyelid fluttering and eyes may drift upward. No post-ictal phase. Duration from 5–20 seconds. | Regular and symmetric generalized usually 3 Hz spike and slow wave complexes ( Figure 4-6 ). |
| Atypical absence | Impairment of awareness often with insidious onsets and offsets. Can have an atonic component. Duration from 5–30 seconds. | Diffuse sometimes irregular spike and wave <2.5 Hz. Can be asymmetric. |
| Myoclonic absence | Rhythmic 2.5–4 Hz jerks, usually of the shoulders, arms, and legs during the absence seizure. Can have peri-oral jerks and an underlying tonic component. Duration is up to 60 seconds. | Regular and symmetric generalized 3 Hz spike and slow wave complexes. |
| Eyelid myoclonia | The first component is spasmodic 4–6 Hz blinking (eyelid myoclonia) often followed by mild impairment in consciousness. Seizures triggered with eye closure in the presence of light or with photic stimulation. Can have a subtle tonic component. Brief, each seizure lasts for seconds. | Generalized 3–6 Hz spike and polyspike and wave discharges that are triggered by eye closure or flickering light. |
| Myoclonic seizures | ||
| Myoclonic | Brief (<100 ms), involuntary, shock-like, often irregular, jerking of the body. Can affect the whole body or just a part. Consciousness is typically not impaired. | Epileptic myoclonus is usually time locked to a generalized polyspike, which is followed by a wave. Myoclonus may not have an EEG correlate ( Figures 5-2 and 5-3 ). |
| Myoclonic atonic | Brief myoclonic jerk followed by atonia (loss of muscle tone). Duration of myoclonic atonic seizure is 1–2 seconds. | Myoclonic jerk correlates with a generalized polyspike; atonia correlates with the after-going slow wave. |
| Myoclonic tonic | A myoclonic jerk or cluster of myoclonic jerks followed by a tonic seizure. Rare. | Myoclonic jerk correlates with a generalized spike, and tonic component may correlate with low-voltage fast activity. |
| Tonic | Sudden onset of a rigid increase in muscle tone, often with stereotyped posturing of the limbs lasting from seconds to minutes. More frequent from sleep. Can be subtle (eye elevation) or massive. Autonomic features are common. | Low-voltage fast activity or 9–10 Hz activity, which may increase in amplitude and decrease in frequency ( Figure 5-4 ). |
| Clonic | Generalized clonic seizures are rare consisting of LOC and bilateral 1–3 Hz rhythmic jerks with the jerk lasting for <100 ms. A clonic seizure differs from myoclonus in that it is rhythmic. Frequency diminishes but amplitude of jerk does not. Lasts from minutes to hours. | Fast activity >10 Hz or occasional spike and wave pattern. |
| Atonic | A sudden loss or decrease of muscle tone, which may be confined to a body part (head), or diffuse, leading to falls. | Electrodecrement, polyspike and wave, or low-amplitude fast activity. |
| Focal seizures | ||
| Focal seizures | Seizure manifestation depends on the area of the brain that is seizing. People may be aware or have clouding of awareness. Symptoms and signs of focal seizures are numerous and varied and can include limb clonus, déjà vu, intense fear, or visual hallucinations. When there is clouding of the sensorium, people may have semi-purposeful picking movements known as automatisms. Focal seizures can spread and secondarily generalize leading to a generalized tonic clonic convulsion. | EEG can show rhythmic activity of varying morphologies from the brain region that is seizing ( Figures 5-5, 5-6, and 5-7 ). In seizures that do not recruit at least 6 cm 2 of cortex, the EEG may show no change from the background on a scalp (not intracranial) recording. |
| Unknown | ||
| Epileptic spasm | Onset of this seizure type is typically before age 1 year. Spasms are brief massive contractions of the axial muscles and can be clinically described as extensor, flexor, or mixed. In a mixed spasm there may be extension of the legs, abduction of the arms, and flexion of the neck. Spasms cluster around sleep transitions. Movement is usually symmetric. Consistent asymmetry implies a possible focal lesion. | The background EEG shows a high-voltage chaotic pattern known as hypsarrythmia. The EEG during a spasm can demonstrate a diffuse slow wave followed by electrodecrement, electrodecrement alone, or generalized paroxysmal low-amplitude fast activity (GPFA) ( Figure 5-8 ). |
Generalized tonic clonic (GTC) seizure. 27-year-old woman with generalized tonic clonic seizures. ( A ) There is diffuse rhythmic fast activity at the seizure onset. ( B ) The patient becomes tonic, and the EEG is entirely obscured by muscle artifact. ( C ) Clonic activity follows with characteristic rhythmic muscle artifact. ( D ) After the seizure, there is postictal slowing. The entire seizure lasted 64 seconds.
Myoclonic epilepsy of infancy. 4-year-old boy with myoclonus since 8 months of age. A bilateral synchronous burst of high-amplitude 4 Hz polyspike and wave (bracket) is more prominent in the parasagittal region for 0.5 sec and then becomes diffuse. A subtle myoclonic shoulder jerk was captured 100 msec after the last spike. Arrows show sporadic spikes, maximal in the parasagittal chain.
Juvenile myoclonic epilepsy (JME). A 17-year-old girl with JME. Generalized irregular 4 Hz spike and polyspike and wave (arrow) in the setting of a normal background. A jerk was reported by the technician during this discharge.
Tonic seizure. 56-year-old male with developmental delay and tonic seizures. Diffuse beta activity (arrow) and admixed EMG artifacts are present for 8 seconds. Clinically correlates with eye opening and subtle raising of his arms.
Mesial temporal lobe epilepsy (MTLE). Onset of a left temporal lobe seizure in a 58-year-old man with left MTS and schizophrenia. Rectangle shows rhythmic left temporal theta activity. After 30 seconds there is diffuse rhythmic activity of mixed frequencies (arrow).
Occipital lobe seizure. A 21-year-old girl with Sturge–Weber syndrome, a left-sided port wine stain, and left posterior leptomeningeal angiomatosis. Onset of her left occipital seizure (arrow) with rhythmic alpha (mimicking a well-organized PDR!) evolves into bilateral occipital theta activity (arrowhead) with admixed spikes. Patient reports seeing a rainbow at onset.
Frontal lobe epilepsy. ( A ) Intracranial recording of a right frontal seizure with a focal onset (arrow) in this 26-year-old man with refractory epilepsy. Clinically very bland with decreased responsiveness. Note postictal slowing (arrowhead). ( B ) Diagram of the 64 contact intracranial electrode grid used in this surgical case. Red indicates seizure onsets and green indicates a focus of interictal spikes or sharp waves. Epilepsy focus was resected and the patient has been seizure free since.
West syndrome. A 4-month-old previously normal baby boy with the development of infantile spasms. Hypsarrythmic background with high amplitude poorly organized chaotic appearing brain waves. A synchronous slow wave correlates with his clinical spasm (arrow) and is followed by electrodecrement.
The next question for discussion is whether or not an individual has epilepsy. Epilepsy is a disease of the brain defined by any of the following conditions: (1) At least two unprovoked (or reflex) seizures occurring >24 h apart; (2) one unprovoked (or reflex) seizure and a probability of further seizures similar to the general recurrence risk after two unprovoked seizures (at least 60%); and (3) diagnosis of an epilepsy syndrome. Of note, if an individual has a history of six seizures, all occurring in the setting of hypoglycemia from accidental insulin overuse, this individual does not have epilepsy. If a child has a single seizure, and the EEG is consistent with BECTS, by criteria #2 and 3, this child has epilepsy.
Following are brief discussions of nine important epilepsy syndromes along with the principal electrographic findings. An epilepsy syndrome or electroclinical syndrome specifically refers to identifiable disorders based upon multiple defining characteristics including but not limited to: age of onset, EEG characteristics, and seizure type. If the clinician is able to make an accurate diagnosis, the particular syndrome has implications for treatment, management, and prognosis. Table 5-2 provides a list of all the electroclinical syndromes and distinctive constellations as defined by the ILAE along with salient clinical and electrographic features.
Table 5-2
Electroclinical syndromes and other epilepsies
| Syndrome Age of onset |
Clinical | EEG |
|---|---|---|
| Neonatal period | ||
| Benign familial neonatal epilepsy (BFNE) 3rd day of life |
Usually clonic seizures, but can be apneic. Neurologically normal. Autosomal dominant. 10–15% progress to epilepsy. Multiple gene loci, usually a K + channel. | Normal background. Theta pointu alternant pattern (theta runs with admixed sharp waves) and multifocal spikes can be seen. |
| Early myoclonic encephalopathy (EME) Birth to several months |
Stimulation-induced and spontaneous myoclonus and focal intractable seizures. Poor prognosis. | Burst suppression pattern. Myoclonus occurs during bursts. |
| Ohtahara syndrome Birth to several months |
Tonic seizures, severe encephalopathy. Majority have severe structural abnormalities. Prognosis is poor. Can progress to IS and LGS. | Burst suppression pattern. |
| Infancy | ||
| Epilepsy of infancy with migrating focal seizures <6 months |
Unprovoked bilateral independent multifocal prolonged partial seizures that are intractable and followed by neurological deterioration. Infants are normal at onset. | Background normal at onset and then deteriorates. Multifocal spikes between seizures. Seizures with multifocal electrographic onsets. |
| West syndrome 3–12 months |
Infantile spasms, developmental regression. Commonly progresses to LGS. | Hypsarrhythmic background. Diffuse slow or sharp wave with electrodecrement, electrodecrement alone or GPFA during a spasm ( Figure 5-8 ). |
| Myoclonic epilepsy in infancy (MEI) 6 months–2 years |
Myoclonic seizures, occasionally myoclonic atonic seizures. 30% have had febrile seizures. Most neurologically normal. Aggressive treatment is postulated to help with overall development. Remits by age 6. | Normal background. Myoclonus is associated with generalized spike and polyspike discharges ( Figure 5-2 ). |
| Benign infantile epilepsy 3–10 months |
Behavioral arrest, automatisms, can secondarily generalize. Remits by age 2. | Normal background. Can have vertex spikes in sleep. |
| Benign familial infantile epilepsy <1 year |
Focal seizures, which may cluster. Easily controlled with medication. Neurologically normal. Autosomal dominant, usually Na 2+ channel. Remits 1–2 years after onset. | Normal background. |
| Dravet syndrome <2 years, peak 6 months |
Heat sensitive GTCC, hemiconvulsions, myoclonic seizures, atypical absence, ataxia, and neurological decline. Majority have SCN1A mutation. | Normal background at onset of disease, which worsens over time. Focal and generalized spikes interictally. |
| Myoclonic encephalopathy in nonprogressive disorders 1 st day–5 years, peak 1 year |
Repeated myoclonic status epilepticus. Focal, hemiclonic, GTCC can occur. Majority have an underlying genetic or structural disorder. Prognosis poor. | Background is slow with multifocal continuous spikes, sharp waves, or slow waves. Myoclonus may or may not correlate with a visible discharge. |
| Childhood | ||
| Febrile seizures plus (FS+) (can start in infancy and continue past age 6) |
Begins with febrile seizures. May have afebrile seizures of multiple types. Neurologically normal. Usually autosomal dominant. | Background normal. May have generalized spike and wave interictally. |
| Panayiotopoulos syndrome 2–8 years, peak 5 years |
Rare nocturnal seizures with autonomic features and eye deviation. Often prolonged. Neurologically normal. Remits in 1–2 years. | Normal background. EEG variable with occipital, centrotemporal, parietal, and even generalized spikes. Discharges activate with sleep, eye closure, or darkness. |
| Epilepsy with myoclonic atonic (previously astatic) seizures 7 months–6 years, peak 2–6 years |
Myoclonic atonic seizures, myoclonus, absence, GTCC, and tonic seizures. Neurologically normal at onset. Most have neurological deterioration. Prognosis is variable. | Background can be normal at onset. Interictal EEG can show generalized epileptiform potentials and parietal theta. Can go into status epilepticus after a GTCC ( Figure 5-9 ). |
| Benign epilepsy with centrotemporal spikes (BECTS) 3–13 years, peak 7 years |
Rare, usually nocturnal seizures with unilateral facial sensations and movements. Can generalize. Normal neurologically. Remits by age 16. | Normal background. Abundant bilateral or unilateral centrotemporal spikes activated by sleep ( Figure 4-11 ). |
| Autosomal-dominant nocturnal frontal lobe epilepsy (ADNFLE) Variable, mean 9 years |
Brief nocturnal frontal lobe seizures can be hypermotor or tonic. Neurologically normal. 30% refractory. Defects in nicotinic acetylcholine receptor subunit genes. | Normal background. May have anterior spikes. Seizures often are surface negative. |
| Late-onset childhood occipital epilepsy (Gastaut type) 3–16 years, peak 5 years |
Frequent brief seizures with visual elementary hallucinations often with postictal migraine. Neurologically normal. 5% will develop recurrent epilepsy. | Mostly occipital spikes and sharp waves, activated by sleep, with eye closure or darkness ( Figure 4-5 ). |
| Epilepsy with myoclonic absences 1–12 years, peak 7 years |
Daily myoclonic absence seizures. GTCC, atonic, and absence seizures can be present. Usually neurologically normal. Cognitive function preserved with seizure control. | Background is normal. Interictal EEG with generalized 3 Hz spike and polyspike and wave. |
| Lennox–Gastaut syndrome (LGS) 1–7 years, peak 3–5 years |
Multiple seizure types, including tonic (most common), myoclonic, GTCC, absence, atonic, and focal. Cognitive impairment. Refractory. | Background with slow spike and wave (1.5–2.5 Hz) ( Figure 5-10 ). MISF and GPFA can be seen. |
| Epileptic encephalopathy with CSWS 2–12 years, peak 4–5 years |
Neuropsychological and behavioral changes. Atypical absence, GTCC, atonic, and partial seizures. Refractory. | EEG shows CSWS with an anterior predominance ( Figure 5-11 ). |
| Landau–Kleffner syndrome (LKS) 1–8 years, peak 3–5 years |
Acquired aphasia presenting between 3 and 8 years. Seizures can occur and are usually easily controlled. Aphasia refractory. | EEG usually shows CSWS with a predominance in the temporal and temporal occipital area. Can have multifocal spikes. |
| Childhood absence epilepsy (CAE) 4–8 years, peak 5 years |
Absence seizures. Neurologically normal. Majority will remit. | Normal background. Can have occipitally predominant rhythmic delta activity. Interictal generalized spikes or spike fragments. Seizures show 3 Hz spike and wave ( Figure 4-6 ). |
| Adolescence–adult | ||
| Juvenile absence epilepsy (JAE) 8–20 years, peak 9–13 years |
Absence seizures, most with GTCC as well. Neurologically normal. Treatment is often lifelong. | Same as CAE (above). |
| Juvenile myoclonic epilepsy (JME) 8–25 years |
Myoclonic seizures, often in the morning. Can have GTCC and absence. Neurologically normal. Easy to treat but usually requires lifelong medication. | Normal background. Interictally majority will have 4-6 Hz generalized polyspike and spike discharges ( Figure 5-4 ). |
| Epilepsy with generalized tonic–clonic seizures alone 5–40 years, peak 11–23 years |
GTCC within 1–2 hours of awakening. Neurologically normal. Usually requires lifelong treatment. | Normal background. Generalized spikes and polypsikes predominantly in sleep. |
| Progressive myoclonic epilepsies (PME) Variable onset |
Heterogenous group of disorders with myoclonus as a seizure type and typically a progressive and devastating course. (See Table 5-3 for more detail.) | Background may be normal at onset but worsens over time. Interictal EEG can show generalized and focal spikes ( Figure 5-12 ). Large somatosensory or visual evoked potentials. |
| Autosomal dominant epilepsy with auditory features (ADEAF) | Focal seizures with buzzing, ringing or sudden inability to understand language. Neurologically normal. Can be a mutation in LGI1 gene. Responsive to treatment. | Background normal. Minority have focal temporal epileptiform potentials interictally. Ictal EEG shows temporal onset. |
| Other familial temporal lobe epilepsies | Temporal lobe seizures with a family history. Neurologically normal. Autosomal dominant. | Usually normal. Focal temporal lobe slowing can be seen. Rare temporal epileptiform potentials. |
| Less specific age relationship | ||
| Familial focal epilepsy with variable foci (infancy to adult) | Each individual has a single focus, but family members may have different foci. Neurologically normal. Responsive to treatment. Autosomal dominant. | Normal background. May have focal epileptiform potentials interictally. |
| Reflex epilepsies | Syndrome in which all seizures are precipitated by sensory stimuli. Syndromes can involve multiple forms of photosensitivity, as well as reading, music, and startle. Can occur in neurologically normal and abnormal individuals. | These epilepsies can either be focal or generalized with either normal or abnormal backgrounds ( Figure 2-10 ). |
| Distinctive constellations | ||
| Mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE with HS) | Typical auras include rising epigastric sensation, déjà vu or fear. Focal seizures with impaired awareness and automatisms. Neurologically normal individuals but some cognitive decline can occur with prolonged epilepsy. Often refractory to medical treatment. | Background may show focal slowing from involved temporal lobe. The majority have interictal anterior temporal sharp waves or spikes. Ictal EEG will often show rhythmic theta or alpha from the involved temporal lobe ( Figure 5-5 ). |
| Rasmussen syndrome | EPC and other focal seizures. Progressive hemiplegia and cognitive decline. Hemispherectomy or hemispherotomy is the treatment of choice. | EEG shows focal slowing and epileptiform potentials on the affected side ( Figure 5-13 ). EPC is often surface negative. |
| Gelastic seizures with hypothalamic hamartoma Variable, peak <12 months |
Gelastic seizures are brief and frequent with bursts of laughing or giggling, can secondarily generalize. Neurologically normal at onset but at risk of deterioration. | Background normal at onset. Can worsen. Interictal spikes are rare and can be focal or generalized. Seizures are typically surface negative. |
| Hemiconvulsion–hemiplegia–epilepsy <2 years |
Onset with a prolonged often febrile hemiconvulsion followed by flaccid hemiplegia, which does not entirely resolve. Subsequent refractory focal epilepsy with cognitive impairment. MRI shows edema followed by atrophy of involved hemisphere. Prognosis poor. | Focal slowing and epileptiform potentials on involved side. |
| Epilepsies that do not fit into any of the above diagnostic categories | These include epilepsies caused by malformations of cortical development, neurocutaneous syndromes, tumors, infections, trauma, angiomas, perinatal insults, strokes, and epilepsies of unknown cause. | EEG depends on particular cause. Seizures can be focal or generalized. Background can be normal or abnormal. |
| Conditions with epileptic seizures that are traditionally not diagnosed as a form per se | ||
| Benign neonatal seizures (BNS) 5th day |
Usually clonic seizures, but can be apneic. Neurologically normal. Seizures remit by 4–6 months of life. | Normal background. Theta pointu alternant pattern (theta runs with admixed sharp waves) and multifocal spikes can be seen. |
| Febrile seizures (FS) 3 months–5 years, peak 18–24 months |
Seizures occurring in the setting of a high fever. Can be simple (<15 minutes, generalized) or complex (>15 minutes, focal, abnormal neurological examination and/or recurrent seizure within 24 hours). Family history common. Slight increased risk of developing epilepsy. | Background normal. |
EPC, epilepsia partialis continua; GTCC, generalized tonic-clonic convulsion; GPFA, generalized paroxysmal fast activity; IS, infantile spasms; LGS, Lennox–Gastaut syndrome; MISF, multiple independent spike foci; CSWS, continuous spike and wave during sleep; SCN1A, alpha subunit of the neuronal type 1 sodium channel.
Epilepsy with myoclonic atonic seizure in a 7-year-old boy. ( A ) The EEG shows a generalized spike (arrows) followed by GPFA (bracket) and then rhythmic slowing and admixed muscle artifact. ( B ) After this seizure he became stuporous, drooling and ataxic. EEG consistent with a spike wave stupor (absence status epilepticus) with continuous high-amplitude 1–2 Hz spike and wave complexes. Mental status improved with very aggressive AED management.
Lennox–Gastaut syndrome (LGS). ( A ) EEG shows frequent epochs with the characteristic slow 1.5–2 Hz spike and wave or sharp and wave (arrows) pattern in this 44-year-old with LGS. There was no clinical correlate with these discharges. ( B ) Multiple independent spike foci (MISF) is another characteristic feature of LGS.
Epileptic encephalopathy with continuous spike wave of sleep (CSWS). Six-year-old girl who began to have behavioral problems in school, developmental regression, and rare seizures. ( A ) Occasional bilateral independent spikes and polyspikes (lines) during wakefulness. Eye blink (arrowhead) and a PDR of 8 Hz are seen. ( B ) CSWS with 1–2 Hz generalized spikes and polyspikes in sleep.
Progressive myoclonic epilepsy (Lafora's disease). 16-year-old boy originally diagnosed with JME because of the presence of generalized polyspikes (arrows), but upon closer inspection a number of features are inconsistent with JME including a suboptimally organized and slow background with right posterior 2 Hz spike and wave (rectangle).
West syndrome
This serious illness typically has its onset between 3 and 12 months, and nearly always before the age of 2 years. The typical spasm consists of a sudden, brief flexion movement of the body with flexion of the neck and abduction of the arms (so-called Salaam seizures). Extension of the neck and lower extremities may occur. The attacks are frequent, occurring in clusters around sleep transitions, and are associated with regression of milestones. Causes are multiple and include cerebral malformations (e.g., agyria, pachygyria), perinatal brain damage, tuberous sclerosis, and a variety of metabolic disorders (e.g., non-ketotic hyperglycinemia). In about 15% of cases, no underlying cause can be identified.
The typical EEG feature is hypsarrhythmia, a more or less continuous, high-voltage (>350 µV), chaotic, slow wave pattern with frequent multifocal spikes and sharp waves ( Figure 5-8 ). Variations of this background pattern, termed modified hypsarrhythmia, are common. These include a burst suppression pattern, focal features (i.e., hemi-hypsarrhythmia), or slow waves without spikes. During the spasm, the most common pattern is a diffuse high-amplitude slow or sharp wave followed by electrodecrement ( Figure 5-8 ), but electrodecrement alone or low-amplitude fast activity can be seen. About half of the patients develop Lennox–Gastaut syndrome (LGS), and at least 80% develop cognitive impairment. Spasms are notoriously difficult to treat. Adrenocorticotropic hormone (ACTH) is highly effective and requires close monitoring due to the potential side effects of hypertension, cushinoid obesity, electrolyte disturbances, cardiomyopathy, or immunosuppression. Vigabatrin is another effective medication for spasms, particularly in children with tuberous sclerosis.
Dravet's syndrome (severe myoclonic epilepsy of infancy)
Infants present with febrile seizures before the age of 2, typically around 6 months. Hot baths, infection, fever, and strong emotion can all trigger seizures. After several months, afebrile convulsions occur followed by the development of myoclonic (onset 1–5 years) and atypical absence seizures. Hemiconvulsions with unilateral clonic activity are characteristic at the onset of the disease but less common in children older than the age of 3. Obtunded states with spike and wave and rare tonic seizures can be present. The infants may be normal at onset but suffer from developmental delay and ataxia as the disease progresses. The EEG background is usually normal at onset and deteriorates over time. Interictally, there can be generalized and focal epileptiform potentials. The disease is associated in the majority of cases with a mutation in alpha subunit of the neuronal type 1 sodium channel (SCN1A). Due to the abundance of this channel on the inhibitory interneurons, any AEDs that act on the sodium channel (including phenytoin, carbamazepine and lamotrigine) can make the seizures worse and even propel the individual into status epilepticus. Agents should be chosen which are broad spectrum AND not sodium channel blockers. The severity of the seizures correlates with the severity of neurological decline and about 90% of children with Dravet are medically refractory. Recently medical marijuana, specifically cannabidiol, is being investigated in the treatment of Dravet as well as LGS.
Benign epilepsy with centrotemporal spikes (BECTS)
This common epilepsy syndrome is easily recognized and also commonly referred to as benign rolandic epilepsy. Onset is between the ages of 3 and 13, and the disorder always remits by age 16. Imaging studies are normal. The neurological examination is normal, as is the EEG background (well-organized with no focal or generalized slowing). There may be a family history.
Common features during seizures include vocalization with guttural sounds, hypersalivation, unilateral oral/facial sensations, and clenching of the teeth. There may be hemifacial movements, hemiconvulsions, and even generalized tonic-clonic convulsions. Seizures typically occur upon falling asleep or upon awakening. Seizures are usually rare in BECTS but a small minority may have frequent events. Subtle neuro-psychological difficulties have been encountered in children with BECTS, typically involving attention and reading. These difficulties are thought to resolve when the interictal EEG improves in mid adolescence.
Epileptiform discharges consist of sharp waves and/or spikes, often biphasic in configuration, occurring in the centrotemporal regions (C3/T3 and/or C4/T4) ( Figure 4-9 ). The discharges may occur in wakefulness but are usually markedly activated by drowsiness and sleep. Isolated sharp waves while awake often transform into grouped or rhythmic discharges during sleep and often alternate between the two hemispheres. There may be a left or right preponderance. Strictly unilateral discharges may also be seen. Rarely, some patients will have generalized discharges as well. Note that the EEG may contain many discharges, although few seizures have ever occurred. Interestingly, these discharges are seen in nearly 1% of children without a seizure disorder and it is estimated that only about 10% of children with centrotemporal sharp waves and spikes go on to develop epilepsy.
There is no universal agreement on treatment. Considering the benign nature of the condition, the debate is whether to treat or not. If treatment is elected, the best therapy may be one that reduces interictal discharges as well as seizures (e.g., levetiracetam, valproic acid).
Lennox–gastaut syndrome (LGS)
LGS has its onset in early childhood, usually around 3–5 years. The classic triad of LGS is cognitive impairment, multiple seizure types, and slow spike and wave (1.5–2.5 Hz) on the EEG. Seizure types include tonic (most common), atonic, myoclonic, focal seizures, and atypical absence. Status epilepticus is not rare and occurs in at least 50% of LGS patients. Typically it is non-convulsive with atypical absence stupor and tonic seizures admixed.
About one-third of cases of LGS are of unknown cause, the remainder being due to congenital malformations, tuberous sclerosis, encephalitis, and perinatal hypoxic brain damage. Infants can first develop West syndrome in infancy and later evolve into LGS.
The EEG typically demonstrates a pattern of generalized slow spike-wave discharges at an average of 2 Hz ( Figure 5-10 ). In addition, multiple independent spike foci (MISF) and generalized paroxysmal fast activity (GPFA) are common.
Treatment of the seizures is difficult. ACTH, the ketogenic diet, multiple AEDs, vagal nerve stimulator, and corpus callosotomy have all been used with variable success. As the clinician struggles to control the seizures, overmedication can occur, which can worsen mentation and balance.
Prognosis is generally poor, and the majority suffer from severe cognitive impairment, even if the seizures are eventually controlled.
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