Electroencephalography

(EEG)A key tool in the diagnosis and

management of‘EPILEPSY’

Margaret Mendez – April 2014

Glossary

Subject Pages

EEG Introduction 1

Epilepsy 2

EEG Patterns in Epilepsy 3-4

EEG Recordings in Partial Seizures 5-9

EEG Recordings in Generalized Seizures 10-21

EEG Neonatal-Generalized Seizure 22

EEG is the abbreviated, daily terminology used for the title, ELECTROENCEPHALOGRAM OR ELECTROENCEPHALOGRAPHY. This test is particularly useful for recording uncontrollable, abnormal brain wave activity associated with epileptic seizures. It is a test that is safe and painless. Electrodes, which are small, metal electrical sources/circuits are attached to your scalp and connected by wires to an electrical box. The electrodes receive and deliver the electrical activity from the brain, which in-turn then are transmitted to a connected EEG recorder for tracing brainwave patterns during the period of the test.

Certain types of EEG wave patterns, whether they be lower to higher, or slower to faster activity, along with localization that occur during a patient’s recording are very useful with the specification of the epileptic disorder. Doctors refer to some specific patterns as ‘epileptiform abnormalities’ or ‘epilepsy waves’. These EEG wave patterns consist of Spikes, Sharp Waves, and Spike-and-Wave discharges, Slow Waves and et al, with relations to assisting in classifying a seizure disorder type.

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ELECTROENCEPHALOGRAM

Epilepsy is a general term used for a group of seizure disorders that cause disturbances of electrical signaling in the brain. Although EPILEPSY is a word often heard after a person has incurred a seizure; a person is not diagnosed without proper evaluation from a physician, has had at least two seizures that were not caused by some other known medical condition, along with other clinical evaluations which usually include an EEG. The word "epilepsy" also does not indicate the cause of the person's seizures & what type or severity they are; as epilepsy can be related to a brain injury, secondary medical disorder, family tendency, or most of the time the cause is unknown – ‘idiopathic’.

An EEG does help with determining seizure types¹ and seizure syndromes² in patients with epilepsy; which in-turn provides assistance with the classifying and management of their epileptic disorder(s). EEG contributes in the diagnosis and classifications of seizure disorders being either Partial (Focal) or Generalized, idiopathic or symptomatic, or part of another unclassified epilepsy category.

The title EPILEPSY is just a general term to which there are several different types of ‘Seizure Disorders’ that fall into this diagnosis. The frequent classification of seizure disorders are split into two categories, Partial and Generalized. In turn, these two categories are divided further into more descriptive Seizures Types (see chart below). This report will give in more details a general definition, description of the type of events a person can experience and the wave patterns that are to be expected to appear on an EEG during a seizure for each of these few types; Simple Partial, Complex Partial and Generalized Absences, Myoclonic, Clonic, Tonic, Tonic-Clonic and Atonic.

¹seizure types = patient’s appearance during seizure event, patient’s personal description (if any) during an event, and what, where & when and event occurs on the EEG recording at the time of a seizure

²seizure syndrome = patient’s age, history and seizure type(s) that appear on the EEG

Epilepsy syndromes are defined by a cluster of features. These features may include:

● The type or types of seizures● The age at which the seizures begin● The causes of the seizures● Whether the seizures are inherited● The part of the brain involved● Factors that provoke seizures● How severe and how frequent the seizures are● A pattern of seizures by time of day● Certain patterns on the EEG, during seizures and between seizures● Other disorders in addition to seizures● The prospects for recovery or worsening

‘EPILEPSY’-Seizure Disorders

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EEG PATTERNS IN EPILEPSY

Along with indicating the location(s) of electrical interference, wave patterns are what also assists in distinguishing the type of seizure disorders, as seizure waveforms do vary.

An easier way of describing is, think of ocean wave forms, as they can range, high, low, loud, quiet, rough, slow & smooth, abrupt and harsh etc. Specific waves are usually a distinction which can indicate the type of events (ex: weather), surroundings or location of the ocean. The EEG too, indicates well-defined patterns of normal or abnormal brain electrical activity, along with the locations. Abnormal patterns may be either Nonspecific or Specific.

‘Nonspecific’ refers to patterns that may be seen in a number of different conditions. For example, certain waves may be seen after head trauma, stroke, brain tumor, or even seizures. ‘Slowing’, in which the rhythm of the brain waves is slower than the rhythm that would be expected for the patient’s age, is a Nonspecific pattern.

‘Specific’ refers to patterns that indicate a tendency toward seizures, as in ‘Epilepsy Waves’ (Spikes, Sharp Waves, and Spike-and-Wave discharges, et al). Although these waveforms may appear similar, yet vary, each type of seizure disorder has a consistent wave form pattern which helps in the diagnosis to a patient. Spikes and sharp waves occurring in a local area of the brain, such as the left temporal lobe, are markers of partial seizures. Spike-and-wave discharges occurring in a widespread area over both cerebral hemispheres, and beginning simultaneously over both hemispheres, are markers of primary generalized epilepsy. In some cases, actual seizures may be recorded during the EEG, particularly in children with absence seizures who are asked to hyperventilate during the test.

That being described, below are titles and measurements of the ‘Specific’ abnormal wave patterns which appear during epileptic seizures.

¹Amplitude = extent; Height of the Wave

²Hz = Hertz or CPS = Cycles Per Second - the unit of Frequency (number of waves) per second

Spikes range from 20 to less than <70 milliseconds (ms) High-amplitude¹

Sharp waves pointed peak and duration of about 70 to 200 ms

Spike-wave complexes (SWCs) are the repetitive occurrence of a Spike followed by a Slow Wave; although a run of 3 seconds is required to classify a record as SWC.

SWCs can be divided further into 2 more specific types: 3-Hz² SWCs and Slow SWCs.3-Hz SWC pattern is characterized by a frequency of 2.5-4 Hz and a very monomorphic (perfectly regular rhythm) morphologySlow SWCs are not only slower than 3-Hz SWCs (< 2.5 Hz) but also more irregular—that is, less monomorphic

Polyspikes are multiple repetitive spikes occurring at about 20 Hz

Hypsarrhythmia is defined as continuous (during wakefulness), high-amplitude (>200 Hz), generalized polymorphic slowing with no organized background and multifocal spikes

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EEG PATTERNS IN EPILEPSY

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PARTIAL SEIZURES, also called Focal seizures, are titled exactly as to what they pertain to; a partial, focalized section of the brain, usually within one hemisphere consisting of electrical disturbances. They consists of abnormal neuron activity restricted to a relatively small region of the brain. These seizures are divided into two types based on the symptoms the patient experiences during an event and the brain waves that appear on an EEG. The two basic partial seizure disorders are titled - Simple Partial and Complex Partial. Partial seizures are the most common type of events experienced by people with epilepsy.

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EEG RECORDINGS OF PARTIAL SEIZURES

EEG RECORDINGS OF PARTIAL SEIZURES

Key Things to Remember about Partial Seizures:Although partial seizures affect each patient in different physical, emotional, or sensory functions of their brain, they both have some things in common:●They don't last long. Most last only a few seconds to a minute or two, although, some people may be confused and need a lot more time (2 to 30 minutes) afterwards to recover fully.● In partial epilepsies, the most important ictal EEG changes for seizure localization are those that occur within the first 30 seconds after the seizure onset.● They end naturally on their own, except in rare cases. The brain has its own way of bringing the seizure safely to an end.● You can't stop them! The normal person should wait for the seizure to run its course and try to protect the patient from any harm until they are alert. *Although, in some emergency cases, doctors may use drugs to bring a lengthy, non-stop, reoccurring partial seizures to an end. ● They are not dangerous to others. The movements produced by a seizure are almost always too vague, too unorganized and too confused to threaten the safety themselves or anyone else.

EEG Patterns in Partial seizures:

•Epileptic discharges begin and remain Unilateral (sometimes can spread to the other hemisphere, if the seizure is to become Generalized)•Usually consisting of repetitive, Rhythmic Spike, Sharp and/or Slow Wave discharges•Most partial seizures can be recorded by scalp electrodes; however, the mesial surfaces may cause difficulty for some recordings

EEG Findings below:

● Periodic Spike and Slow Wave discharges occurring in the posterior, right temporal location

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Simple Partial Events: consists in which consciousness or awareness is retained (no loss of consciousness). Sudden jerking, twitching, numbness or tingling can occur, particularly on one side of the body; psychic symptoms (hallucinations, déjà vu). This seizure disorder, especially most common in children can be more difficult to diagnose without full evaluation and testing. An Aura* may also occur and progress to a generalized seizure, in which case the classification category is Partial-(simple or complex)- into secondarily-Generalized seizure.

Simple Partial Seizures are characterized by:

● Person remaining consciousness during the event● Commonly consist of rhythmic or semi-rhythmic clonic activity of the face, arm or leg● Experience of unusual feelings or sensations

*Aura : A sensation that is known as the onset, warning before a seizure, is also called a simple partial seizure when it occurs within seconds before another generalized seizure. At times an Aura may appear alone and not progress, at which time it then represents a seizure in its own.

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EEG RECORDINGS OF PARTIAL SEIZURES

Complex Partial Events: Consciousness is impaired or responsiveness may diminish during this seizure which can lasts 30 seconds to a few minutes. They are common in both children and adults. It can consist of warning (most typical is sensation in stomach, numbness), automatisms (such as lip smacking, picking at clothes, fumbling), unaware of environment (may wander, amnesia of the events, mild to moderate confusion during), and possibly appear drowsy after seizure with no recollection of the event.

Complex Partial Seizures are characterized by:• Impaired consciousness can occur; may appear awake, yet unresponsive (dream-like)• Having a change during the event and loss of full consciousness• Psychic symptoms more often are a component• Sudden and unexplainable feelings of joy, anger, fear, sadness, or nausea• Altered senses of hearing, smelling, tasting, seeing, or feeling of things that are not real• Strange repetitious behaviors such as blinks, twitches, and mouth movements

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EEG RECORDINGS OF PARTIAL SEIZURES

EEG RECORDINGS OF PARTIAL SEIZURES

TEMPORAL LOBE seizures are typically defined as simple partial seizures, which do not cause loss of awareness, and complex partial seizures, which do. Although they can lead into generalized seizures. These seizures may occur after brain injury or infection, such as meningitis or encephalitis. Sometimes, they are caused by stroke or the presence of a brain tumor or are diagnosed as idiopathic, cryptogenic.

Temporal Lobe Events:Temporal lobe seizures cause behaviors such as smacking of the lips or rubbing the hands together. Other features of the seizures may include, staring, déjà vu, emotional or thought disturbances and hallucinations - involving sounds, smells, or tastes.

EEG Patterns in Temporal Lobe seizures:

•Usually consists of Spike or Sharp-waves•Anterior frontal-temporal (either right or left = F7,T3 or F8,T4)•Focal temporal discharges are usually activated by sleep deprived

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Image above shows the EEG finding during interictal state of MTLE; a typical epileptiform abnormality with spike or sharp wave with negative polarity and followed by a slow wave.

Generalized is a classification in which the seizures are widely spread over both hemispheres of the brain, especially when they begin in both at the same time. Although each of these seizure classifications are categorized as generalized and occur throughout both hemispheres, they each have different signs, symptoms, EEG patterns and also differ based upon the age of the patient. Therefore, each generalized type is titled and further distinguished separately.

This category of seizure disorders consists of several types, some particular being titled; Myoclonic, Clonic, Tonic, Tonic-Clonic, Atonic and both Typical & Atypical Absence seizures disorders.

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EEG RECORDINGS OF GENERALIZED SEIZURES

ABSENCE seizures, also called in the past ‘Petit-mal seizures’,falls into two different categories, Typical and Atypical, which are indications of primary and secondary description of events that occur within Absence seizures. These seizures are more common in children.

Absence Events:

Both typical and atypical absences share many characteristics: ● Starting abruptly - without an aura● Lasts less than 30 seconds● End abruptly ● Consists of staring, unresponsive, frequent eye blinking, lip smacking, decrease in tone, and automatisms

Typical Absence Seizure-EEG patternAtypical Absence Seizure-EEG

pattern

EEG Patterns in Typical Absence Seizures:

● Sudden onset of 3-Hz generalized spike-and-wave or multiple spike-and-slow wave complexes**Frequency tends to be faster (about 4 Hz) at the onset, and slower (down to 2 Hz) toward the end of discharges, if they persist longer than 10 seconds.● Voltage of the discharges is often maximal in the fronto-central regions. ● Easily induced by hyperventilation in more than 90% of the patients.

EEG Patterns in Atypical Absence Seizures:

● More heterogeneous, showing 1.5- to 2.5-Hz Slow Spike-and-Wave● May be irregular or asymmetric● No characteristic location of maximal discharges

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EEG RECORDINGS OF GENERALIZED SEIZURES

EEG RECORDINGS OF GENERALIZED SEIZURES

TONIC seizures consist of sudden stiffness of limbs, which often causes the person to lose balance and fall. Along with stiffening of limbs, will occur flexion of certain arm and leg joints, and possible grunting sounds. These seizures are usually short and last a few seconds, although they are the usual onset of Tonic-Clonic seizures (as discussed further).

Tonic Seizures Events:Tonic seizures usually last less than 20 seconds. The child’s muscle tone increases and the body and limbs make sudden stiffening movements. These seizures most often occur during sleep.

EEG patterns in Tonic Seizures:

• Rapid Spikes with High Amplitude throughout• Frequency ranging from 10 to 25 Hz

CLONIC seizures are very similar to Myoclonic, although they are characterized with repetitive jerks of muscle groups throughout any part of the body , along with lasting longer, ranging anywhere from several seconds to two minutes.

Children’s Clonic Seizures Events:With clonic seizures, the child’s muscle(s) jerk repeatedly. These movements cannot be controlled by restraining the child or repositioning the arms and legs.

EEG patterns in Clonic seizures:

•Spike or Spike-Wave discharges usually match the frequency of the body jerks•Frequency of the seizure discharge is usually rhythmic

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EEG RECORDINGS OF GENERALIZED SEIZURES

Tonic-Clonic- This stereotyped epileptic ‘fit’(a.k.a. grand mal seizures), exhibits a number of well defined stages. First a loss of consciousness occurs, then a loss of body tone and a consequent fall. This type of seizure first causes the person to stiffen up muscles (Tonic phase), generally followed by uncontrollable Clonic jerking or twitching. Typically these seizures end spontaneously after a few minutes, and afterward the person may appear drowsy and confused. Tonic-clonic seizures can occur at any age and are encountered with numerous forms of epilepsy, including generalized idiopathic forms.

Generalized tonic-clonic seizures are characterized by five distinct phases that occur in a child. The body, arms, and legs will flex (contract), extend (straighten out), tremor (shake), a clonic period (contraction and relaxation of the muscles), followed by the postictal period. During the postictal period, the child may be sleepy, have problems with vision or speech, and may have a bad headache, fatigue, or body aches. The final phase in which consciousness is regained may last anywhere between 2 and 30 minutes. Sometimes these seizures are preceded by  an aura (a partial seizure itself), in which case the seizure is secondarily generalised.

EEG Patterns in Tonic-Clonic seizures:

•Usually begin with Rapid Spikes that slow in frequency after a few seconds, which indicates the Tonic phase•As spikes slow down, they become Spike-Waves and represent the Clonic phase

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EEG samples of both Tonic and Clonic seizure patterns, along with muscles artifacts which usually occur in between each phase.

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EEG RECORDINGS OF GENERALIZED SEIZURES

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EEG RECORDINGS OF GENERALIZED SEIZURES

MYCLONIC seizures consist specifically of single jerks or a quick series of jerks of muscles throughout any part of the body, particularly the upper shoulders. This seizure disorder can be diagnosed to infants, children and adults.

EEG Patterns in Myoclonic seizures::

•High-voltage of Poly-spike waves that usually lasts less than a second, followed byslow-waves•Bursts of the waves may occur single or in a quick series •Can be rhythmic or non-rhythmic

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EEG RECORDINGS OF GENERALIZED SEIZURES

Juvenile Myoclonic Epilepsy (JME) seizures occurs at the age of 12 years until 13, of which then is usually classified further as Tonic-Clonic seizure disorder. The seizure event can consist of quick, sudden, small jerks of the legs, arms or shoulders - particularly the upper limbs.

EEG Patterns in Juvenile Myoclonic seizures:

•High-voltage of Poly-spike waves (4-5 Hz) that usually lasts less than a second, followed by slow-waves•Often occur in Stage I sleep•Epileptiform findings can be triggered by hyperventilation and/or intermittent photic stimulation

EEG Finding below:

A 12 year old patient having high amplitude, poly-spike waves within a 1 second period, followed by slow-wave activity throughout, along with indications of myoclonic jerks 

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EEG RECORDINGS OF GENERALIZED SEIZURES

EEG RECORDINGS OF GENERALIZED SEIZURES

Atonic seizures are consistent with a sudden loss of muscle tone. The seizure can range from mild - consisting of eyelids drooping, head nodding, shoulders slumping and the person dropping things; to dramatic - brief loss of postural tone, often resulting in falls, the most severe form of which is known as “drop attacks”. The seizures are brief - usually less than fifteen seconds. Atonic seizures are known to occur at any age, and are always associated with diffuse cerebral damage, learning disabilities and are common in severe symptomatic epilepsies. *Atonic seizures usually begin in childhood and are often seen in syndromes like Lennox Gastaut syndrome.*

EEG Patterns consists of:

EEGs are irregular and show, one or a mix of, waveforms.•Slow Spike-waves, intermittent desynchronized flattening or polyspikes followed by flattening

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EEG RECORDINGS OF GENERALIZED SEIZURES

*LENNOX-GASTAUT SYNDROME (LGS) is a rare epileptic encephalopathy which consist of combined seizure patterns, which include; Atypical, Atonic, Tonic (especially during sleep) and Myoclonic seizures. Its severity can be nonresponsive to treatment and occurs in two-thirds of the patients diagnosed. The syndrome typically develops after 3 years of age, and often evolves from other epilepsy syndromes, such as *West syndrome.

EEG Patterns in Lennox-Gastaut seizure:

Figure 1: showing slow spike-and-waves (1.5-2.5 Hz) associated with atypical absences.

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LENNOX-GASTAUT SYNDROME (LGS) CONT.

Figure 2: EEG of a patient with LGS, showing low-voltage, high-frequency patterns seen during tonic spells, which are especially common during sleep. *Delta waves that follow indicate patient was sleeping.

EEG RECORDINGS OF GENERALIZED SEIZURES

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LENNOX-GASTAUT SYNDROME (LGS) CONT.

Figure 3:

EEG RECORDINGS OF GENERALIZED SEIZURES

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West Syndrome, also called ‘infantile spasms’, is a severe epilepsy syndrome composed of the triad of flexor, extensor or mixed (asymmetrical) spasms, an electroencephalogram is a central tool in the diagnosis. West syndrome is an age-dependent expression of a damaged brain, and most patients with infantile spasms have some degree of developmental delay. The term infantile spasm has been used to describe the seizure type, the epilepsy syndrome, or both.

SymptomsIn nine out of 10 children with the condition, infantile spasms occur in the first year of life, typically between three and eight months old. To begin with, the attacks are usually brief and infrequent and do not occur in clusters. Therefore it is quite common for the diagnosis to be made late. The first diagnosis is often colic, because of the pattern of the attacks and the cry that a child gives during or after an attack can mimic gastrointestinal discomforts.

EEG RECORDINGS OF GENERALIZED-NEONATAL

SEIZURES

EEG Patterns in West Syndrome seizure: This EEG shows Hypsarrhythmia, a chaotic pattern of continuous, high-amplitude polymorphic, rapid spikes, high-voltage generalized slowing and other abnormalities. Often sleep is the period of seizure occurrence.

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