Dr. Amit VatkarMBBS, DCH, DNB Pediatrics

Fellow in Pediatric Neurology, MumbaiTrained in Neurophysiology & Epilepsy,

USA

Contact No. : +91-8767844488Email: vatkaramit@yahoo.com

NEUROPHYSIOLOGY OF SEIZURES AND EEG

NEUROPHYSIOLOGY

Initiation Phase :

1. High frequency bursts of AP

2. Hyper synchronization

Bursting activity :

Long lasting depolarisation of Neuronal

membrane due to influx of EC Ca2+

Opening of Na+ channels

influx of Na+

Generation of repetitive AP

PROPAGATION PHASE :

1.Increased in EC K+ (Blunts hyperpolarization and

depolarise neighbouring neuron)

2. Accumulation of Ca2+ in presynaptic terminals (enhanced NT release)

3. Depolarisation – induced Activation of the N- methyl – D Aspartate (Ca++ influx * Neuronal activation)

Mechanisms for Bursting Activity :

Intrinsic to Neuron :

Changes in

• conductance of ion channels

• response characteristics of membrane receptors

• Cytoplasmic buffering

• Second messenger systems

• Protein expression as determined by gene transcription, translation and post translational modification

Extrinsic to Neuron :

Changes in

1.Amount or type of NT present at the synapse

2. Modulation of receptors by EC ions and other molecules

3. Temporal & spatial properties of synaptic and non synaptic input

Mechanism of origin of generalised spike and wave discharges in Absence Seizures

Related to oscillatory rhythm (by circuits connecting thalamus & cortex)

Oscillatory behaviour involves an interaction between GABA -B receptor, T-Type Ca2+ channels and K+ channels located within thalamus

Mechanism of Epileptogenesis :

Transformation of a normal neuronal network into one that is chronically hyper excitable CNS injury Lowering of seizure threshold Structural changes in Neuronal networksEg. I - MTLE

1) highly selective loss of neurons 2) Reorganisation or sprouting of surviving neuron II - Head Injury Alterations in intrinsic bio chemical properties o cells eg. Chr changes in Glutamate Receptor function

MECHANISM OF INTER ICTAL AND ICTAL EVENTS

APPLIED IMPORTANCE :

AED appear to act primarily by blocking the initiation of spread of seizures

Inhibition of Na+ dependent AP – phenytoin CBZ, Lamotrigine, Topiramate

Inhibition of voltage gated Ca++ channels – phenytoin

Decrease glutamate release – Lamotrigine

Potentiation of GABA receptor function Benzodiazepine

Increased in availability of GABA valproic acid, gabapentin, Tiagabine

Inhibition of T. type Ca2+ channels in thalamic neuron – Ethosuximide, valproic acid

DefinitionDefinition

EEG Stands for EEG Stands for ElectroencephalographyElectroencephalographyEEG signals are based upon the movement of EEG signals are based upon the movement of

electrical charges in biological tissue. electrical charges in biological tissue. These electrical charges are associated with These electrical charges are associated with

ions (+ve or ions (+ve or ––ve charged) such as sodium ve charged) such as sodium (Na), potassium (K).(Na), potassium (K).

This activity is actually a measure of the This activity is actually a measure of the brainbrain’’s s function function rather than rather than structurestructure..

Definition Contd..Definition Contd..

EEG typically is the recording of potential EEG typically is the recording of potential differences between two points (with one or differences between two points (with one or both electrodes on the scalp)both electrodes on the scalp)

Amplitude scale typically in microvolts (Amplitude scale typically in microvolts (V)V)Typical EEG, as recorded from the surface of Typical EEG, as recorded from the surface of

the head is attenuated by ~75% from direct the head is attenuated by ~75% from direct cortical recordings. cortical recordings.

Compared with ECG (typically in the mV Compared with ECG (typically in the mV range), EEG signal is 1000 times smaller range), EEG signal is 1000 times smaller

Complexity of EEG is greater than ECG and Complexity of EEG is greater than ECG and not as clearly definednot as clearly defined

Electrode PlacementElectrode Placement

Ten Twenty SystemTen Twenty SystemIn 1958 it was decided there should be an In 1958 it was decided there should be an

internationally agreed system for the internationally agreed system for the placement of EEG electrodesplacement of EEG electrodes

Known as the 10/20 system.Known as the 10/20 system.Certain anatomical landmarks on the skull, Certain anatomical landmarks on the skull,

such as the nasion, inion and preauricular such as the nasion, inion and preauricular notches are used to determine the relative notches are used to determine the relative positioning of electrodes.positioning of electrodes.

Electrode PlacementElectrode Placement

Ten Twenty SystemTen Twenty SystemEEG Technician measures the skull and EEG Technician measures the skull and

marks positions usually with chinagraph marks positions usually with chinagraph pencil.pencil.

Points marked at the appropriate 10% and Points marked at the appropriate 10% and 20% intervals.20% intervals.

Relative distance Relative distance between pairs of between pairs of electrodes remains the same, regardless of electrodes remains the same, regardless of absolute head size.absolute head size.

Electrode caps based upon the 10-20 Electrode caps based upon the 10-20 system may also be used for clinical system may also be used for clinical recording. recording.

Electrode PlacementElectrode PlacementA : Lateral left-sided view of headB: Superior view of headC: 10-10 International System (or extended 10-20 System)

• Even Numbers: correspond to right hemisphere• Odd Numbers: correspond to left hemisphere• Subscript Z: corresponds to the midline• Numbers increase laterally from the midline

Abbreviations:N: NasionFp: Frontal polarAF: Antero-Frontal (Anterior Frontal)F: FrontalFT: Fronto-Temporal (Frontal-Temporal)FC: Fronto-Central (Frontal-Central)T: TemporalC: CentralTP: Temporo-Parietal (Temporal-Parietal)CP: Centro-Parietal (Central-Parietal)P: ParietalPO: Parieto-Occipital (Parietal-Occipital)O: OccipitalI: InionPg: Nasopharyngeal

Electrode PlacementElectrode Placement

Special Note:

Ambiguous labels between 10-20 & 10-10 System

T7 T3

P7 T5

T8 T4

P8 T6

Electrode PlacementElectrode Placement

Signals (commonly referred to as Signals (commonly referred to as tracestraces) are ) are generally recorded between pairs of electrodes generally recorded between pairs of electrodes on both hemispheres of the brain.on both hemispheres of the brain.

Recording from pairs of adjacent electrodes Recording from pairs of adjacent electrodes commonly referred to as commonly referred to as bipolarbipolar

Recording of electrode potentials with respect Recording of electrode potentials with respect to a default or global reference electrode to a default or global reference electrode referred to as referred to as monopolar, unipolar or monopolar, unipolar or referentialreferential

They are measured in linked chains of bipolar They are measured in linked chains of bipolar electrodes from front to back and transversely electrodes from front to back and transversely across the head.across the head.

Convention regards the polarity as Negative, Convention regards the polarity as Negative, such that a negative potential difference is such that a negative potential difference is represented by an upward deflection in the represented by an upward deflection in the trace. trace.

EEG Frequency Bands

Alpha 8.1 – 13 Hz

Beta ~13 – 20 Hz

Theta 4.1 – 8 Hz

Delta 0.5 – 4 Hz

Gamma* ~20 - 55 Hz* Frequencies in Gamma range or higher often referred to as

high frequency Beta

EEG is commonly divided into following frequency bands:

EEG and AgeEEG and Age

Normal EEG has alpha as the dominant Normal EEG has alpha as the dominant frequencyfrequency

In infants and young children, may observe a In infants and young children, may observe a predominance of theta activity or low predominance of theta activity or low frequency alphafrequency alpha

In the elderly, also may have a tendency to see In the elderly, also may have a tendency to see some slowing in background activity, again some slowing in background activity, again alpha-theta boundaryalpha-theta boundary

Some epilepsy syndromes have specific EEG Some epilepsy syndromes have specific EEG changes that are only present within specific changes that are only present within specific age rangesage ranges

EEG EEG shouldshould be interpreted with some be interpreted with some background knowledge of the patient, and age background knowledge of the patient, and age is an important discriminant between what is an important discriminant between what may be acceptable as a normal EEG variant may be acceptable as a normal EEG variant and a specific abnormalityand a specific abnormality

EEG MontagesEEG Montages

EEG signals are typically represented as a EEG signals are typically represented as a series of waveforms on paper or monitorseries of waveforms on paper or monitor

They represent the potential difference They represent the potential difference between electrodes pairsbetween electrodes pairs

The order and sequence of these The order and sequence of these waveforms are defined as waveforms are defined as montagesmontages

Montages are particularly useful in that Montages are particularly useful in that the magnitude and orientation of the EEG the magnitude and orientation of the EEG generators that may not be clearly generators that may not be clearly defined in one montage may become defined in one montage may become apparent in another.apparent in another.

ReferentialReferential EEG trace of interest is defined by the difference EEG trace of interest is defined by the difference

between the specific electrode (ie. O1) and a between the specific electrode (ie. O1) and a cephalic reference point referenced to a single cephalic reference point referenced to a single electrode.electrode.

i.e. Fp2 i.e. Fp2 –– REF, Fp1 REF, Fp1 –– REF, etc. REF, etc.DifferentialDifferential EEG trace is defined by electrode referenced to EEG trace is defined by electrode referenced to

another (more proximally located) electrode on another (more proximally located) electrode on the head ie Fp2 the head ie Fp2 –– F4 F4

Differential (commonly referred to as Differential (commonly referred to as BipolarBipolar) is ) is the most flexible montage type and is most the most flexible montage type and is most commonly used or modified for assessing focal commonly used or modified for assessing focal EEG abnormalities.EEG abnormalities.

EEG MontagesEEG Montages

Types of EEG RecordingTypes of EEG Recording

Routine EEGRoutine EEG20 – 30 minute test20 – 30 minute testScreeningScreeningEyes Open & Eyes ClosedEyes Open & Eyes ClosedIncludes provocative techniquesIncludes provocative techniques

Types of EEG RecordingTypes of EEG Recording

Ambulatory EEGAmbulatory EEGPatient is fitted with a small recorder Patient is fitted with a small recorder

for 24 hours – patient can then have for 24 hours – patient can then have their EEG recorded whilst in their their EEG recorded whilst in their normal environmentnormal environment

Types of EEG RecordingTypes of EEG Recording

Long term MonitoringLong term MonitoringTypically ranges from 3 hours to 5 days. Typically ranges from 3 hours to 5 days.

(Generally no longer than 2 weeks)(Generally no longer than 2 weeks)Performed if Routine EEG recording shows Performed if Routine EEG recording shows

nothing, but clinical history of seizures nothing, but clinical history of seizures suggestivesuggestive

extended recording, usually with video used extended recording, usually with video used to try to record unusual activity. to try to record unusual activity.

Clearly define the relationship between Clearly define the relationship between electrical EEG changes and clinical eventselectrical EEG changes and clinical events

NOTE:NOTE: A large percentage of patients with epilepsy may A large percentage of patients with epilepsy may display normal EEG until an actual episode or “attack” display normal EEG until an actual episode or “attack” occurs, extended recording along with supervised occurs, extended recording along with supervised modifications to medications may be required to clearly modifications to medications may be required to clearly elucidate the seizure typeelucidate the seizure type..

Visual EEGVisual EEG Assessment Assessment

Determine dominant frequency of background Determine dominant frequency of background activityactivity

Determine dominant amplitudeDetermine dominant amplitude

Compare reactivity to eye opening compared Compare reactivity to eye opening compared to background (ie. while eyes are closed)to background (ie. while eyes are closed)

Establish symmetry of activity from both Establish symmetry of activity from both hemispheres as well as comparison between hemispheres as well as comparison between cerebral lobescerebral lobes

Discriminate sharply contoured waves or Discriminate sharply contoured waves or spikes as arising from artefact or as truly spikes as arising from artefact or as truly abnormal activityabnormal activity

Compare reactivity to provocative techniques Compare reactivity to provocative techniques of photic stimulation and hyperventilationof photic stimulation and hyperventilation

Provocative Techniques ActiveProvocative Techniques Active

HyperventilationHyperventilation Patient breathes deeply, continuously, for Patient breathes deeply, continuously, for

typically about 3 minutes.typically about 3 minutes.Hyperventilation rapidly removes COHyperventilation rapidly removes CO22 from from

the blood stream and modifies blood pH the blood stream and modifies blood pH levels slightlylevels slightly

Blood vessels constrictBlood vessels constrictPronounced EEG slow activity is observedPronounced EEG slow activity is observedThis increased synchronisation may evoke a This increased synchronisation may evoke a

seizure in certain individualsseizure in certain individuals

Example of generalised slowing associated with hyperventilation.

Photic StimulationPhotic StimulationHigh Intensity light presented to patient at High Intensity light presented to patient at

various frequencies (1-40 Hz) for brief various frequencies (1-40 Hz) for brief intervals (typically 5-10 seconds)intervals (typically 5-10 seconds)

Small percentage of patients with epilepsy Small percentage of patients with epilepsy are are photo-sensitivephoto-sensitive – may have episodes – may have episodes that are precipitated by flickering light.that are precipitated by flickering light.

Normal EEG variant – Normal EEG variant – Photo DrivingPhoto Driving where where changes in EEG show a direct frequency changes in EEG show a direct frequency locked response to stimulation.locked response to stimulation.

Provocative Techniques ActiveProvocative Techniques Active

Example of photic driving, maximal activation from occipital electrodes, and discharges clearly locked to stimulus.

Sleep DeprivationSleep Deprivation Most generalised epilepsies are enhanced by Most generalised epilepsies are enhanced by

slow wave sleep, and some focal epilepsies are slow wave sleep, and some focal epilepsies are likely to generalise from the abnormal area.likely to generalise from the abnormal area.

Sleep deprivation is likely to exacerbate such Sleep deprivation is likely to exacerbate such seizures and therefore it may provide a higher seizures and therefore it may provide a higher yield of detecting an EEG abnormality from a yield of detecting an EEG abnormality from a routine EEG if patient is deprived of sleep prior routine EEG if patient is deprived of sleep prior to recording.to recording.

Commonly used technique for hospital Commonly used technique for hospital inpatients when undergoing long-term inpatients when undergoing long-term monitoring for diagnostic or pre-surgical monitoring for diagnostic or pre-surgical workupworkup

Provocative Techniques PassiveProvocative Techniques Passive

Maturation of EEG in children :

1.Posterior Dominant rhythm maturation

2. Hyper ventilation higher amplitude slow activity

3. Posterior slow waves of youth

4. More theta anteriorly

5. Hypnagogic hypersynchrony

6. Sharp & high voltage sleep activity

E.E.G IN EPILEPSY

IDEAL IN EVERY PATIENT1. DIAGNOSIS OF EPILEPSY-ABSENCE EPILEPSY

BENIGN ROLANDIC EPILEPSYMYOCLONIC EPILEPSY

2. TYPE OF SEIZURE3. LOCALISATION IN PARTIAL SEIZURE4. ETIOLOGY - LESIONAL EPILEPSY

ENCEPHALOPATHY - PLEDS - HEPATIC - SSPE - HSE - CJD

5. FOLLOW UP6. STATUS EPILEPSY

Epileptiform Discharge :

Different from the surrounding activity

High voltage

Asymmetrical with a longer and larger second half

Has more than one phase

Tend to have an after going slow wave

Epileptiform Discharges :

1.Spike

2.Sharp wave

3. Spike and wave complex

4. Polyspike & wave complex

5. Sharp & slow wave complex

6. Polyspike complex

7. Multiple sharp wave complex

8. Synchronous spike and wave discharges

9. Asynchronous discharges

SPIKE SHARP SPIKE & WAVE SHARP & SLOW WAVE

SLOW SPIKE AND WAVE

POLY SPIKE AND WAVE

MULTIPLE SHARP AND SLOW WAVE

POLY SPIKE MULTIPLE SHARP COMPLEXES

EEG features in various Epilepsy

I – Simple Partial seizures

Normal in 60 – 80 %

In some patients, periodic sharp activity or very focal rhythmic activity limited to only a few electrodes.

II – Complex partial seizures :

Mesial frontal / orbito frontal origin

- may be without scalp EEG changes

Temporal lobe origin brief discharges termed epileptiform spikes or sharp waves

III - Generalised Absence Seizures :

High voltage

Frontally dominant

Synchronous, symmetrical, regular and rhythmic 2.5 to 4 Hz Spike and wave activity

IV - Generalised atypical absence Seizures

Frequency < 2.5 Hz

Slight post ictal slow activities

Asymmetrics are common

More regional distribution anteriorly

V – Generalised tonic seizure :

Generalised 10- Hz rhythmic activity or

Generalised high frequency low voltage activity

VI - Generalised atonic seizure :

Brief generalised spike and wave

discharges followed immediately

by diffuse slow waves

VII – Generalised tonic clonic seizure :

Tonic phase :

10 Hz rhythmic discharge that evolves into high amplitude generalised polyspike discharges.

Clonic phase :

High amplitude activity is typically interrupted by slow waves to create a spike and wave pattern

VIII – Infantile spasm :

Begins with abrupt generalised

eletro decremental response of EEG

with generalised attenuation of

back ground frequencies with

superimposed beta or alpha range

activity lasting from < 1 sec to

several seconds

IX – Juvenile Myoclonic Epilepsy :

Bilaterally synchronous fast 4-6 Hz

spike & wave discharges synchronous with myoclonus

X – Lennox – Gastaut syndrome

Slow posterior background

Slow generalised spike and wave

activity at 1.5 – 2 Hz (hall

mark)

EEG PATTERNS IN SELECTED SPECIFIC CONDITIONS

Herpes Simplex encephalitis :

Periodic lateralised epileptiform discharges in temporal or fronto temporal area

SSPE : (Subacute sclerosing Pan Encephalitis)

Long interval generalised periodic discharges

Hypoxic Ischemic encephalopathy

1.Generalised asynchronous / bisynchronous slow activity

2.Generalised attenuation

3. Alpha coma

4. Theta coma

5. Spindle coma

6. Periodic discharges may be synchronous or independent

7. Burst suppression pattern

epochs of relative flattening of back ground (suppression) alternating with epochs of

mixed frequency EEG activity (bursts)

LIMITATIONS OF EEG

NORMAL EEG. DOES NOT RULE OUT NORMAL VARIANTS MISTAKEN FOR

EPILEPSYNOT SENSITIVE FOR STRUCTURAL LESIONNOT A GOOD GUIDE FOR

- SEIZURE CONTROL- DRUG WITHDRAWAL

ALWAYS CORRELATE CLINICALLY

Dr. Amit VatkarPediatric Neurologist, Navi Mumbai

MBBS, DNB

Email: vatkaramit@yahoo.comContact No.: +91-8767844488

Visit us at: http://pediatricneurology.in/

THANK YOU !