Steve S. Chung, MD, FAANChairman, Neuroscience Institute

Director, Epilepsy ProgramBanner University Medical Center

University of ArizonaPhoenix, AZ

Beyond the Basics in EEG Interpretation:

Throughout the Life Stages

Topics To Be Covered

• Review of benign variants of EEG

• How to recognize benign vs. abnormal

• Pitfalls in adult EEG interpretation

• Review of EEG in neonates

• Normal patterns and developmental markers in neonates

• Pitfalls in neonate EEG interpretation

Benign Variants

• Rhythmic Midtemporal Discharges

• Subclinical Rhythmic Theta Discharges in Adults

• Temporal Slowing in Elderly

• Posterior Slow Waves of Youth

• Midline Theta Rhythm

• Frontal Arousal Rhythm

• Fourteen- and Six-Hertz Positive Bursts

• Small Sharp Spikes

• Six-Hertz Spike and Wave (Phantom S & W)

• Wicket Spikes

Rhythmic Mid-temporal Discharges

• Psychomotor variant

• Rhythmic 4-7 Hz theta waves (monomorphic)

• During drowsiness or stage 2 sleep (disappears with alerting)

• Commonly unilateral, usually shifting sides

• Duration: 1-10 seconds (can be minutes)

• 0.35% to 2% of normal adolescents and adults

• Different from seizure due to:

• Lack of evolution of frequency, amplitude, morphology

• No clinical events

SREDA: Subclinical Rhythmic Theta Discharges in Adults

• Rarely seen in patients over age 50

• Rhythmic, sharply contoured 5-7 Hz, at 40-100 V

• Wide-spread, bilateral more commonly

• Maximal at parietal and posterior temporal regions or over the vertex

• Average duration of 40 to 80 seconds

• Usually during wakefulness but also in sleep

• Different from seizures due to:

• No clinical events

• No organized progression

• No post-event slowing

Temporal Slowing in Elderly

• Bitemporal but more frequently over the left hemisphere

• Slowing of theta range (delta slowing is abnormal)

• Intermittent

• May persist after eye opening

• About 35% after age 50

• No clear relationship with vascular disease

Posterior Slow Waves of Youth

• Most often seen between age 8-14

• About 15% of age 15-30

• Intermixed with posterior background but does not distort it

• Diminishes with eye opening and disappears during sleep

• Can be slightly asymmetrical

Posterior Slow Waves of Youth

Midline Theta Rhythm

• Sinusoidal, archiform, or sharply contoured 4-7 Hz

• Focally over midline anterior (max at Fz or Cz)

• During wakefulness, drowsiness, or after arousal

• Not usually seen over the temporal region

• Wax and wane for several seconds

• Very rare (0.01%)

Midline Theta Slowing

Frontal Arousal Rhythm

• In adults: monophasic 7-10 Hz waves for several seconds with spindle-like morphology

• In younger children: 4-5 sinusoidal pattern can be seen

• In older children: faster

• May evolve from beta activity

• May last longer than 10 seconds (shorter in adults)

Fourteen- and Six-per-Second Positive Bursts

• First appears at age 3 and maximally expressed at age 12 to 15

• Benign variants during drowsiness and light sleep

• Positive phase over the occipital or posterior temporal area (surface positive polarity)

• Duration is less than 1 second

• Usually occur independently on the two sides (asynchronous), or sometimes unilateral

• 6 Hz (6-8 Hz) and/or 14 Hz (12-16 Hz)

14 Hz

6 Hz

14 Hz

14 Hz

Small Sharp Spikes

• Benign epileptiform transients of sleep (BETS)

• Benign sporadic sleep spikes (BSSS)

• Low amplitude and short duration (<50 µV, <50 msec)

• Abrupt ascending and steep descending, no slow waves

• Anterior to mid-temporal regions

• During drowsiness and stage II sleep

• Unilateral or bilateral with shifting

• Occur singly and not in trains

• 20%-25% of healthy subjects (adolescence to adults)

FP1-F7

F7-T3

T3-T5

T5-O1

FP2-F8

F8-T4

T4-T6

T6-O2

FP1-F3

F3-C3

C3-P3

P3-O1

FP2-F4

F4-C4

C4-P4

P4-O2

1 SEC. 50 UV

Phantom Spike and Wave

• Also known as six-hertz spike and wave

• Brief bursts of 5-7 Hz generalized spike and wave discharges

• Primarily in adolescents and young adults

• During wakefulness and drowsiness

• FOLD: female, occipital, low amplitude, drowsiness

• WHAM: wakefulness, higher amplitude, anterior, male

• 0.2% to 4.5% of healthy subjects

Mu Rhythm

• Pre-central rhythm of 7 to 12 Hz

• Comb-like morphology, may be asymmetric

• Unaffected by eye opening or closure

• Attenuates with movements, thought of movements, and tactile stimulation of contralateral limbs

• Mental task and fatigue attenuates

• 20% young adults; slightly more common in women

Wicket Spikes

• Monophasic, archiform

• 6-11 Hz transients

• Anterior or mid-temporal region

• Unilateral or bilateral (usually asymmetrical)

• During wakefulness or sleep

• Longer trains during wakefulness and drowsiness

• 0.9% to 2.9% of normal adults

• Different from temporal lobe spikes due to absence of following slow waves and morphology

Lambda Waves

• Bi- or tri-phasic transients over occipital area

• Elicited by looking at a patterned design in a well-illuminated room

• More common in children and adolescents

• May be asymmetrical

• Attenuates with eye-closure, reducing illumination and patterns

Low Voltage EEG

• Amplitude <20 uV overall

• Can be normal (4%-9% of nl adults)

• May be associated with VBI, extrapyramidal syndromes, psychiatric illness, alcoholism, myxedema, and head injury

Interpretation of Neonatal EEG

First, establish and look for:

• Continuity of EEG

• Bilateral Synchrony

• Behavioral states

• Developmental markers

Behavioral States

Waking Active sleep Quiet sleep

Eye Movements

Blinks, etcRapid, phasic

None

Body Movements

Frequent Frequent Infrequent

Respiration Variable Irregular Regular

Distinct EEG Milestones

• Delta Brushes

• Temporal theta/alpha bursts

• Occipital theta

• Frontal sharp transients

• Rhythmic frontal delta

• Tracé discontinu

• Tracé alternant

• Interhemispheric synchrony

Tracé discontinu

• Timing

• Early prematurity to 34-36 weeks

• Low amplitude (<30 uV) epochs alternating with bursts including mixed delta/theta, delta brushes, temporal theta, sharp transients

• Active segments increase with increasing CA

Tracé discontinu

Average Duration of Discontinuous Period During NREM Sleep

Levin KH, Luders HO. 2000.

Levin KH, Luders HO. 2000.

Tracé alternant

• Progression from T.D. with increasing CA

• Interburst intervals attenuated, not quiescent

• 3-6 second bursts high amplitude delta/theta (1-6 Hz, 50-150 uV) with low amplitude beta

• Interburst: moderate amplitude mixed frequencies (4-12 Hz, 25-50 uV)

• Seen in QS at term

Tracé alternant

Developmental Markers of EEG

Trace Alternant

Frontal Sharp Wave Transients

Vertex Transients

Sleep SpindlesBeta Delta Complexes

Temporal

Theta

Bursts

TemporalAlpha Bursts

Occipital Dominant

Alpha Rhythm

Levin KH, Luders HO. 2000.

Interhemispheric Synchrony

• At 30-32 weeks CA, 50%-60% bursts synchronous

• At term, 100% synchronous (during T.A. in QS)

Interhemispheric Synchrony

Development of EEG Synchrony

Levin KH, Luders HO. 2000.

Active Sleep

Quiet Sleep

Excessive Asynchrony

Excessive Asynchrony

Developmental Markers of EEG

Trace Alternant

Frontal Sharp Wave Transients

Vertex Transients

Sleep SpindlesBeta Delta Complexes

Temporal

Theta

Bursts

TemporalAlpha Bursts

Occipital Dominant

Alpha Rhythm

Levin KH, Luders HO. 2000.

Temporal Theta/Alpha Bursts

• Timing

• Onset: 26 weeks

• Maximum: 29-31 weeks

• Rare after 35-36 weeks

• Sharply contoured 4.5-6 or 8-9 Hz, 50-100 uV

• Frequently bilateral, synchronous

Temporal Theta and Alpha Bursts

Temporal Theta Bursts Temporal Alpha Bursts

Levin KH, Luders HO. 2000.

Delta Brushes (Beta-Delta Complex)

• 32-35 weeks CA

• Spindle frequency (8-22 Hz) superimposed on 0.5-1.5 Hz delta waves

• May be asynchronous, asymmetric

• Central early (32 weeks)

• Occipital/temporal later

• Gone by several weeks pre-term

Beta Delta Complex (“Delta Brush”)

Delta Brushes (Beta-Delta Complex)

0

5

10

15

20

25

30

35

40

45

50

26-30 31-32 33-34 35-36 37-38 39-42

AS

QS

Frontal Sharp Transients (Encoches Frontales)

• Biphasic frontal sharp waves (- then +)

• During sleep, esp transition ASQS

• Timing

• Appear 35 weeks CA

• Persist several weeks post-term (6 weeks)

• 50-150 uV, 200 msec

• Bilateral and synchronous, may be asymmetric

Frontal Sharp Waves

Normal Temporal Sharp Transients (42 GA)

Normal vs Abnormal Temporal Sharps

Normal Abnormal

Amplitude <75 uV >75 uV

Duration <100 msec >150 msec

Frequency <1 per min >3 per min

Morphology Mono- or biphasicPolyphasic, slow

waves

Polarity Surface negative Surface postive

State NREM Awake and NREM

Occurrence Random, bilateralIn runs, consistently

focal

Abnormal Sharp Waves (34 GA)

Neonatal Seizure Patterns

What Are These Patterns on a Neonatal EEG?

Hiccups

Patting baby Sucking a bottle

Electrode artifacts

Pitfalls in Interpretation of Newborn EEG

• Normal activity called “epileptiform”

• Frontal sharp transients

• Rhythmic frontal delta activity

• Temporal theta bursts

• Distinguish normal discontinuity from burst-suppression patterns

• Don’t overcall amplitude asymmetries or asynchrony of bursts in TA