3Mansoura University Hospitals EEG Teaching CoursesTamer Belal, MD ,PHDLecturer of NeurologyMansoura University Hospitals
4Uses of ambulatory EEGEvaluation of interictal epileptiform activityDocumentation of seizures of which patients are unawareEvaluation of response to therapyEvaluation of nocturnal or sleep-related eventsEvaluation of suspected pseudoseizuresEvaluation of syncope
8Normal EEG waves Delta 0-4 Theta 4-8 Alpha 8-13 (5-100uv) Type Frequency (Hz)LocationNormallyPathologicallyDelta0-4frontally in adults, posteriorly in children;high amplitude wavesadults slow wave sleep (deep sleep)in babiesHas been found during some continuous attention taskssubcortical lesionsdiffuse lesionsMetabolic encephalopathy hydrocephalusdeep midline lesionsTheta4-8Found in locations not related to task at handyoung childrendrowsiness or arousal in older children and adultsAssociated with inhibition of elicited responses (has been found to spike in situations where a person is actively trying to repress a response or action)focal subcortical lesionsmetabolic encephalopathydeep midline disorderssome instances of hydrocephalusAlpha8-13(5-100uv)posterior regions of head, both sides, higher in amplitude on non-dominant side. Central sites (c3-c4) at restRelaxed/reflectingClosing the eyesAlso associated with inhibition control, seemingly with the purpose of timing inhibitory activity in different locations across the brain.Attenuated by eye opening, attention and mental effort (Alpha block)Alpha Coma (unresponsive)Paradoxical alphaInterside differences˃50% (lt)Unilateral failure of the alpha rhythm to attenuatereflects an ipsilateral abnormality (Bancaud’s phenomenon
9Normal EEG waves Beta ˃13-30 ˂35uv Gamma 30-100+ Mu 8-13 Type Frequency (Hz)LocationNormallyPathologicallyBeta˃13-30˂35uvboth sides, symmetrical distribution, most evident frontally; low amplitude wavesalert/workingactive, busy or anxious thinking, active concentrationBenzodiazepinesGammaSomatosensory cortexDisplays during cross-modal sensory processing (perception that combines two different senses, such as sound and sight)Also is shown during short term memory matching of recognized objects, sounds, or tactile sensationsA decrease in gamma band activity may be associated with cognitive decline, especially when related the theta band; however, this has not been proven for use as a clinical diagnostic measurement yetMu8-13Sensorimotor cortexCz and PzShows rest state motor neuronsDuring wakefulnessAttenuated by contraction of contralateral musclesWhen persistent, unreactive, and associated with focal slowing, mu like frequencies are abnormalMu suppression could indicate that motor mirror neurons are working. Deficits in Mu suppression, and thus in mirror neurons, might play a role in autism
15The 5 principles of localization Rule 1Widely placed electrodes record larger voltages than closely placed electrodesThe potential recorded from the pair having one electrode at F will be greater than the potential recorded from the pair having neither electrodes at FRule 2The further away the dipole is from the surface of the scalp the smaller will be the potential observed at the surface, inter-electrode distance being constantRule 3Phase reversal is really an instrumental one and no true phase reversal. The reversal results from the fact that the shared electrodes goes to opposing inputs and hence causes the opposite deflection to occurRule 4Rule 5If two Electrodes are equidistant from the focus, no voltage will be recorded between them (Cancellation)
16The 5 principles of localization Widely placed electrodes record larger voltages than closely placed electrodesThe potential recorded from the pair having one electrode at F will be greater than the potential recorded from the pair having neither electrodes at FThe further away the dipole is from the surface of the scalp the smaller will be the potential observed at the surface, inter-electrode distance being constantPhase reversal is really an instrumental one and no true phase reversal. The reversal results from the fact that the shared electrodes goes to opposing inputs and hence causes the opposite deflection to occurIf two Electrodes are equidistant from the focus, no voltage will be recorded between them (Cancellation)
18Commonly seen localization patterns A Phase reversal observed in a line of referentially connected electrodes is a true phase reversal . The longer the deflection associated with a particular focus of activity, the closer is the electrode to the focusContamination results from a significantly active F included in the reference electrode.
19Commonly seen localization patterns (A) Bipolar montage demonstrating phase reversal and (B) referentialmontage demonstrating absolute voltage.
20Commonly seen localization patterns EEG demonstrating bipolar (A) and reference (B) montages to illustrate a left anterior temporal sharp wave.
21Commonly seen localization patterns The rules governing polarity and convention relative to “pen”deflection. When input 1 is negative the deflection is up.
22EEG ReadingBoth the background activity and the changes that appear in the features of the tracing are described in the following termsFrequency: fast, slow, monomorphic, polymorphic or periodicAmplitude :low ˂20uv, Medium 20-5-uv, high˃50uvAttenuation and blocking, suppression , paroxysmalWave shape (morphology) : transients (sharp, spike) or complex, monomorphic , polymorphicSymmetry (synchrony)Location : focal , generalized or lateralizedContinuity : continuous or intermittentReactivity
23Writing the EEG report Two parts 1- Actual description f the EEG findings and their interpretation2- Clinical correlation that render the report meaningfulBrief history of the clinical findings todayMention what the referring physician hope to find outDescriptive details regarding the testing situationDescribe the state of the patientDescribe the EEG ( just descriptive)Impression : normal or abnormal and define abnormalityAttempt to correlate the EEG with clinical pictureSuggest further study if needed
24Writing the EEG reportThe EEG was recorded with the standard system of electrode placement. The patient was awake and cooperative.EEG Report : Background activity comprises of alpha activity 9-10 c/s, which is symmetrical in the occipital leads and spreading anteriorly interspersed with fast beta activity. No paroxysmal activity seen. Hyperventilation and photic stimulation is non-contributory.IMPRESSION: Normal record. No epileptiform activity seen. Clinical correlation advised.Note: A normal EEG does not rule out the diagnosis of epilepsy, as epileptiform discharges may be paroxysmal.
25Abnormal EEG Patterns Abnormality of background rhythm Abnormal sleep patternsAbnormal slow activity:Generalized intermittent slow activityFocal and lateralized intermittent slow activityPersistent slow activityParoxysmal epileptogenic abnormalitiesInter-ictal epileptiform discharges( focal, generalized)IctalSecondary bilateral synchronyEpileptiform patterns of doubtful significanceAbnormal periodic paroxysmal patternsGeneralized periodic paroxysmal patternsSSPE,CJD,Herpes S E, suppression patterns, Triphasic wavesLateralized periodic paroxysmal patternsPLEDS,BPLEDS
26The Normal EEG Patterns Alpha rythmAlpha frequencyNormal 10-Hz alpha rhythm “blocked” by eye opening and returning on eye closure. Note the faster frequency immediately on eye closure (“squeak”).
27The Normal EEG Patterns Note the prominent left central mu rhythm during eye opening (Mu rhythm)
28The Normal EEG Patterns Breach rhythm in the right temporal region (maximal at T4) following craniotomy for temporal lobectomy
29The Normal EEG Patterns Normal frontocentral theta rhythm in an 18-year-old patient while awake.
30The Normal EEG Patterns Bi-occipital lambda waves in a 28-year-old patient with dizziness.Notice the frequent “scanning” eye movement artifact in the F7 and T8 derivations.
31The Normal EEG Patterns Intermittent left mid-temporal delta during transition to drowsiness in a normal 84-year-old patient evaluated for syncope
32The Normal EEG Patterns NORMAL SLEEP ARCHITECTUREPOSTS appearing in the lower three channels in a bipolar circle montage demonstrating positive polarity in the occipital region during sleep.Notice the surface negative vertex waves maximal at Cz
33The Normal EEG Patterns NORMAL SLEEP ARCHITECTUREStage 2 sleep with prominent sleep spindles and POSTs
34The Normal EEG Patterns NORMAL SLEEP ARCHITECTURESlow-wave sleep. Note the intermittent POSTs and sleep spindles against the continuous delta background
35The Normal EEG Patterns NORMAL SLEEP ARCHITECTUREREM sleep with rapid eye movements associated with lateral rectus spikes is noted at the F7 and F8 derivations
36The Normal EEG Patterns ACTIVATION PROCEDURES Normal build-up during hyperventilation
37The Normal EEG Patterns ACTIVATION PROCEDURES Normal 10-Hz alpha rhythm “blocked” by eye opening and returning on eye closure. Note the faster frequency immediately on eye closure (“squeak”).
38The Normal EEG Patterns BENIGN VARIANTS OF UNCERTAIN SIGNIFICANCERhythmic temporal theta bursts of drowsiness.Note the sharply contoured morphology.
39The Normal EEG Patterns BENIGN VARIANTS OF UNCERTAIN SIGNIFICANCECentral theta (maximal at Cz) seen during the awake state in a 35-year-old patient with migraine headaches
40The Normal EEG Patterns BENIGN VARIANTS OF UNCERTAIN SIGNIFICANCEA 6-Hz (phantom) spike-wave burst with frontal predominance in the 5th second of this EEG in an awake patient with temporal lobe epilepsy.
41The Normal EEG Patterns BENIGN VARIANTS OF UNCERTAIN SIGNIFICANCEFourteen- and 6-Hz positive bursts maximal in the T6 electrode derivation in a linked-ears reference montage. Note the downward deflection and prominent 14-Hz frequency
42The Normal EEG Patterns BENIGN VARIANTS OF UNCERTAIN SIGNIFICANCEA right benign Epileptiform transients of sleep (BETS) in the temporal region during stage 2 sleep. Note the higher amplitude in the T1 and T2 channel with a longer interelectrode distance
43The Normal EEG Patterns BENIGN VARIANTS OF UNCERTAIN SIGNIFICANCEWicket waves maximal at T3 and T4
45Normal EEG Variants Refer to waves that are rare or unusual but not generally abnormal. They may be unusual in shape or in distribution.They can includewave mixtures that can appear unusual and can confuse the casual reader (for example, wave harmonics)Artifacts or electrical disturbances from structures that are not in or part of the brain and do not affect the brain or its function but appear in the EEG tracing
46Normal EEG Variants Odd-Looking WaveformsPsychomotor variant (rhythmic harmonic theta)Mu (rhythm en arceau or wicket rhythm, arciform rhythm )14- and 6-Hz wavesSmall sharp spikes of sleep (SSS) , benign epileptiform transients of sleep (BETS). posterior occipital transients of sleep POSTS6-Hz spike and wave (phantom spike and wave)Wicket spikesSubclinical rhythmic EEG discharges in adultsRhythmic midline theta
47Normal EEG Variants Odd-Looking WaveformsPsychomotor variant (rhythmic harmonic theta)Asymmetrical runs of theta or delta activity primarily in the mid-temporal regions, lasting for a few seconds or as long as 30-45occurs in 0.5% to 2.0% of selected normal adults and consists of bursts or runs of 5- to 7-Hz theta waves that may appear sharp, flat, or notched in appearanceIt starts suddenly on 1 side and lasts for several seconds before terminating suddenly. This behavior resembles a seizure discharge, hence the name "psychomotor variant."Generally considered benign, this waveform does not correlate with seizure disorder. It is best seen on a prolonged EEG and tends to be more common in children and young people
48Normal EEG Variants Odd-Looking WaveformsPsychomotor variant (rhythmic harmonic theta)Rhythmic temporal theta bursts of drowsiness. Note the sharply contoured morphology.
49Normal EEG Variants Odd-Looking WaveformsMu (rhythm en arceau or wicket rhythm, arciform rhythm )This waveform is recognized easily and has no pathological significance. The naive may not recognize it and assume it to be abnormalThe mu waveform occurs in the central regions in the awake patient. It is seen best if a bone defect underlies the electrodesIt can be markedly asymmetricalOften in the alpha range frequency, it has rounded positive aspects on 1 side and sharpened negative aspects on the otherIt is not blocked by eye openingIt becomes obvious when the alpha disappears (ie, alpha blocking).Associated with fast activity, mu has a frequency about half that of fast activity.The most classical feature of mu waveform is that it blocks with motor activity of the contralateral body (or the thought of such movement).
50Odd-Looking Waveforms Normal EEG Variants Odd-Looking Waveforms14- and 6-Hz wavesThe 2 frequencies are intimately intertwined and the complexes occur in bursts.They generally are thought to be clinically insignificant.They occur in healthy children and adolescents. Some claim that they are best seen in referential recordings during sleepSmall sharp spikes of sleep (SSS)This waveform also is known as benign epileptiform transients of sleep (BETS).These sharp, small waves occur on 1 or both sides (often asynchronously), especially in the temporal and frontal regions.Rarely seen in children, they are seen most often in adults and the elderlyThey can occur in epileptic patients but often are seen in healthy individuals. They can be regarded as a probable normal variant
51Odd-Looking Waveforms Normal EEG Variants Odd-Looking Waveforms6-Hz spike and wave (phantom spike and wave)These occur as bursts of miniature spike and wave complexes or runs of such complexes at 6 Hz rather than the usual 2-4 Hz.Their significance is debated, but generally those occurring in the posterior head regions are regarded as benignSeen at all ages (but especially in adults), they often are confused with 14- and 6-Hz waves and may merge into themThe anterior variety are regarded by some as consistent with epilepsy, but further studies are needed to confirm thisWicket spikesAlmost exclusively in adultsLike wicket rhythm, (rounded aspects to 1 side and sharp points to the other, giving the appearance of spikes or sharp wavesdistinguished by their morphology and at times by their defined background rhythms, which are harmonizing.Can be seen either in wakefulness or sleep in the anterior or temporal head regions.
52Odd-Looking Waveforms Normal EEG Variants Odd-Looking WaveformsSubclinical rhythmic EEG discharges in adultsSREDA consists of theta rhythm occurring in a widespread manner, maximal over the parietal and posterior temporal regions, and lasting for a few seconds to a minute without clinical signs or symptoms.It is described as "not evolving" and appears quite stable for its duration.Mechanism of SREDA is not understood, represent a benign EEG phenomenon that distinguished from seizure dischargesAnother unusual variant (delta rhythm as well as notched waveforms with a frontal distribution and a more prolonged duration that even includes sleep(FRIDA)Rhythmic midline thetaRhythm maximal at the midline, most prominently at CzIt has a frequency of 5-7 Hz and typically has an arciform, spiky, mu like appearanceWaxes and wanes, can appear during wakefulness or drowsiness, and is usually reactive to eye opening or limb movement
53Normal EEG Variants ArtifactsForehead, jaw, and eyelid muscle movements homotor variant (rhythmic harmonic theta)Tongue and eyes have their own dipole electric chargeu (rhythm en arceau or wicket rhythm)Sweating produces electrical disturbances by shorting electrode pairs.Other sources of artifacts include ambient electrical waves from respirators, intravenous pump machines, televisions, and other electrical equipment.
54Normal EEG Variants ArtifactsMany are recognized by their characteristic appearance on the tracing, but others are identified by direct inspection and reported by the technologist or identified on the video tracing in video-EEG recording.Artifacts show great variation because of their protean origin.They may be single waves or recurrent waves (eg, intravenous infusion running), while others are prolonged disturbances (eg, sweating).
55Artifact produced by tongue movement EEG artifact of eye blinking.Example of EEG chewing artifact
56Normal EEG Variants ArtifactsThe following can be regarded as clinically insignificantChewing produces spurious spike and wave runs in the frontal and temporal regions from the temporalis musclesSweating produces very slow waves, because the salt solution shorts out pairs of adjacent electrodesEye movements occur with blinking and result from the electrical charge of the eye itself (see image below). They are frontal. Nystagmus also produces artifactual wavesECG and pulse motion produce unusual waveforms. ECG produces small spikes that are recurrent and are especially evident in the monopolar montages.
57Normal EEG Variants ArtifactsThe following can be regarded as clinically insignificantTremor and movement of the head or body may cause electrodes to moveElectrode pops or movements can produce sudden, recurrent, or continuous electrical wavesElectrical fields result from electrical devices and televisions.ICU special waveforms may result from respirator-induced movements, intravenous drips and drip pumps, electrical fields, or cautery in the operating room or emergency department.
58Normal EEG Variants HarmonicsEEG is a complex summation of many frequenciesDifferent frequencies sometimes add to or cancel each other, creating odd waveforms or fluctuations of waveformsPseudospikes or pseudoslow waves may be seen with intermixing of waves.Many fascinating patterns have been generated by mixing artificially created computer-generated frequencies.These waveforms have the significance of the basic waveforms that underlie the patterns.
59Central theta (maximal at Cz) seen during the awake state in a 35-year-old patient with migraine headaches
60A 6-Hz (phantom) spike-wave burst with frontal predominance in the 5th second of this EEG in an awake patient with temporal lobe epilepsy.
61Fourteen- and 6-Hz positive bursts maximal in the T6 electrode derivation in a linked-ears reference montage. Note the downwarddeflection and prominent 14-Hz frequency.
62A right benign epileptiform transients of sleep (BETS) in the temporal region during stage 2 sleep. Note the higher amplitude in the T1 andT2 channel with a longer interelectrode distance.