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Dr. Amit VatkarMBBS, DCH, DNB Pediatrics
Fellow in Pediatric Neurology, MumbaiTrained in Neurophysiology & Epilepsy,
USA
Contact No. : +91-8767844488Email: [email protected]
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: [email protected] No.: +91-8767844488
Visit us at: http://pediatricneurology.in/
THANK YOU !