Neurology - EEG Basics, Maturation & Abnormalities

Question 1

What are the indications for neonatal EEG?

Answer 1

• Assess cerebral maturation
• Detect seizures
• Assess response to treatment
• Assess severity of cerebral dysfunction
• Determine prognosis

Question 2

Neonatal v Adult EEG

Answer 2

• Skull thickness (neonate skull is thin allowing for better transmission of low frequency signals like Delta waves; adults have thick skulls but more organised activity)
• Myelination + sulcation (neonates have incomplete myelination → slower conduction of neural signals resulting in slow activity and underdeveloped alpha/beta waves, which is opposite to adults)
• Sleep states (neonates alternate b/w active + quiet sleep whereas adults have defined sleep stages)
• Reactivity (neonates have limited reactivity with delayed responses to stimuli, opposite to adults with clear responses)
• Background activity (neonates have discontinuous activity with bursts of high amp. waves separated by periods of inactivity - trace discontinu/IBIs, whereas adults have continuous activity)
• Seizures (appear subtle with rhythmic discharges in neonates, epileptiform patterns may be normal in neonates but abnormal in adults)
• Metabolic + oxygenation differences (neonates have high metabolic demand but developing O2 supply leaving them vulnerable to hypoxic-ischaemic events, whereas adults have efficient blood flow regulation and O2 delivery)

Question 3

Neonatal electrodes

Answer 3

10:20 system
Disposable, hydrogel
Extra-cerebral: EOG, ECG, EMG, Resp, SpO2

Question 4

Neonatal EEG Montages

Answer 4

Full head (used for characterisation of seizures and encephalopathy) v Limited (used for TH protocol and prolonged recordings >24h)

Question 5

Need-to-know Info for Neonatal EEGs

Answer 5

• Gestational + Chronological age of the baby (PMA)
• Hx of pregnancy issues
• Hx of perinatal asphyxia (Apgar score)
• Occurrence of seizure-like activity
• Medication
• State of the baby (asleep/awake/medicated/incubated/ventilated)

Question 6

Neonatal EEG procedure

Answer 6

• 10:20 system
• Skin prep
• Secure electrodes with CPAP hat/headwrap
• Notch filter on + second ground if necessary
• Frequently check skin integrity

Question 7

Technical parameters of neonatal EEG

Answer 7

Filters 0.3-70Hz
Sensitivity 7uM/mm

Question 8

Possible artifacts on EEG

Answer 8

Biological:
- Respiratory
- Heartbeat
- Patting/rocking
- Hiccups
Non-biological:
- ECMO machine
- Ventilator
- Overhead heater
- Mains
- High-frequency oscillator

Question 9

EEG in suspected seizures

Answer 9

• For diagnosis = up to 24h (or until paroxysmal seizures detected)
• For monitoring = for at least 24h after last seizure
• Both continuous EEG

Question 10

Paroxysms that raise seizure suspicion

Answer 10

• Focal tonic or clonic movements
• Intermittent forced gaze deviation
• Myoclonus (sudden, brief jerking movements)
• Generalised tonic posturing (symmetrical body tensing/stiffening)
• “Swimming” movements of upper limbs/”bicycling” movements of lower limbs
• Unexplained apnoea or pallor, high BP, cyclic periods of tachycardia

Question 11

EEG correlations with neonatal seizures

Answer 11

• Can be eletrographic only with no clinical signs (silent seizures) - very common
• Most are focal rather than generalised
• Feature rhythmic/repetitive spikes, sharp waves, slow waves, or evolving (increase in amp. & frequency and spread over time) rhythmic discharges
• Short duration (10s-2m)

Question 12

Possible causes of seizures in neonates

Answer 12

• HIE (most common)
• Intracranial haemorrhage
• Infections (Meningitis)
• Metabolic disorders (hypoglycaemia/hypocalcaemia)
• Genetic/epileptic syndromes

Question 13

EEG features of neonatal seizures

Answer 13

• Focal rhythmic discharges (most common; spike-and-wave or sharp waves in a local region, can evolve in frequency/amplitude, seen in HIE/stroke)
• Periodic/semi-periodic discharges (repetitive, rhythmic activity in regular intervals seen in metabolic disorders/infections/severe brain injury)
• Burst suppression with seizures (high voltage bursts separated by low voltage suppression where seizures arise from bursts, seen in HIE)
• Multifocal seizures (multiple independent seizure foci across different brain regions seen in severe brain injury)
• Electrographic only seizures (no clinical signs but clear EEG seizure activity, seen in very pre-term/critically ill neonates)

Question 14

EEG features of electrographic seizures

Answer 14

Rhythmic activity evolving in frequency, amplitude, and morphology. No clinical signs.

Question 15

BIRDs

Answer 15

Brief, (potentially) ictal, rhythmic discharges
- Resemble seizures but are short, rhythmic sharp activity (<10s, >4Hz)
- Occur in sick or premature neonates
- Part of the ictal-interictal continuum
- Associated with later electrographic seizures (sign of seizure risk, marker for seizure onset zone) and abnormal developmental outcomes

Question 16

Amplitude-Integrated EEG (aEEG)

Answer 16

Peak to peak amplitude derived from a single channel showing brain activity over time. The signal is filtered through a 2-15Hz filter, rectified, compressed, and displayed with a time-based of 6cm/hour.
Pro: useful to assess background activity (continuous/discontinuous/burst suppression/flat trace)
Con: less sensitive, can miss focal seizures, can give false positives.
- More of a screening/monitoring tool

Question 17

EEG Continuity

Answer 17

Continuous waves along the page w/o flat periods

Question 18

EEG Synchrony

Answer 18

Bursts of activity happening at the same time in both sides of the brain

Question 19

EEG Symmetry

Answer 19

Bursts of activity happening at the same frequency and amplitude on both side of the brain

Question 20

Inter-Burst Intervals (IBIs)

Answer 20

Discontinuous periods of suppression/flat line activity in between bursts of high voltage activity. Should shorten with age, abnormal if >50-60sec

Question 21

Trace Discontinu

Answer 21

Highly discontinuous pattern seen in active + quiet sleep in very premature and pre-term infants <34 weeks PMA.
- IBIs
- Disappears after 32-34 weeks PMA

Question 22

Trace Alternant

Answer 22

Seen in full-term neonates during quiet sleep
- Alternating high voltage slow waves w/ low voltage activity every 4-10sec (discontinuous pattern)
- Associated with continuous pattern during wakefulness + active sleep (unlike Trace Discontinu)
- Disappears at 46-48 weeks PMA (becomes more continuous, slow wave)
- Result of maturing sleep regulation

Question 23

Delta brushes

Answer 23

Normal finding in pre-term infants, suggests normal cerebral maturation with reduced Delta Brushes seen in HIE or severe brain injury, however persistent Delta Brushes at term suggests delayed maturation
- Slow Delta waves with superimposed fast Beta activity (Beta-Delta complexes)
- Appear at 26-36 weeks gestation, peak at 30-32 weeks gestation
- Prominent in central + occipital regions

Question 24

EEG features in extremely premature babies (24-27 weeks PMA)

Answer 24

• Trace discontinu (discontinuous activity)
• Can last >10sec in very pre-term
• Occurs in active + quiet sleep
• Disappears by 32-34 weeks PMA and EEG pattern becomes more continuous
• Result of immature cortex + underdeveloped connectivity

Question 25

EEG features in very premature babies (28-30 weeks PMA)

Answer 25

More synchrony present - Shorter IBIs (5-10sec) - Some bursts show bilateral synchrony - Sleep differentiation begins with early signs of active + quiet sleep

Question 26

EEG features in moderately premature babies (31-33 weeks PMA)

Answer 26

Delta Brushes - More continuous but still intermittent - Very short IBIs <5sec - Better sleep differentiation with quiet sleep showing Trace Alternant

Question 27

EEG features in late premature babies (34-36 weeks PMA)

Answer 27

Near continuous pattern - Clear sleep states (active v quiet) - Still have Trace Alternant in quiet sleep - Well-defined Delta Brushes - Mainly bilateral synchrony

Question 28

EEG features of full term babies (>37 week PMA)

Answer 28

Mature neonatal EEG - Mostly continuous in wakefulness and active sleep - Still have Trace Alternant in quiet sleep but shorter pauses - Stable sleep-wake cycles with REM and non-REM stages emerging - Fading Delta Brushes

Question 29

Abnormal neonatal EEG features

Answer 29

Background activity showing: - Persistent IBIs (abnormal >50-60sec, should reach 6sec at full term) - Depressed/attenuated voltage (only Delta/Theta waves present), lack of differentiation in sleep/wake cycles - Electrocerebral silence (isoelectric recording, quadruple check electrodes, impedances, stimulation to be sure) - Suppression burst activity (synchronous bursts alternating w/ isoelectric background - hallmark of epileptic encephalopathy) - Excessive discontinuity (loss of sleep-wake cycle, IBI amp >10mV, HIE) - Persistent focal sharp waves and spikes (Positive Rolandic sharp waves)

Question 30

Poly-frequency

Answer 30

Presence of multiple different frequencies at once (Alpha, Beta, Delta, Theta) - absence = severe brain insult (HIE, haemorrhage, encephalopathy, meningitis)

Question 31

Rolandic sharp waves

Answer 31

(Centrotemporal Spikes) - Brief, high amplitude sharp/spike wave discharges - Maximal of centrotemporal (Rolandic) region - Typically seen in non-REM sleep - Activated by drowsiness and sleep - Associated with Rolandic Epilepsy (Benign Epilepsy with Centrotemporal Spikes - BECTS) in 3-13yo that remits in adolescence

Question 32

When do the 3 states of consciousness (sleep differentiation) begin?

Answer 32

From 28 weeks PMA onwards, before this - the EEG looks the same all the time and is highly discontinuous with long IBIs and Trace Discontinu

Question 33

When does the neonatal EEG become completely continuous?

Answer 33

By week 46 PMA at the most, the EEG should be completely continuous. From 37-46 weeks PMA there may be some discontinuity seen, particularly during quiet sleep. Continuous activity should start to emerge at 28-32 weeks PMA becoming progressively prominent thereafter

Question 34

Features of an awake state EEG background

Answer 34

30-32 weeks PMA: continuous with low voltage activity. 35 weeks PMA: continuous with higher voltage activity and more poly-frequencies.

Question 35

Features of active sleep state EEG background

Answer 35

30-36 weeks PMA it is mainly continuous Delta + Theta activity. 38 weeks PMA there is a mixture of faster frequencies too

Question 36

Features of quiet sleep state EEG background

Answer 36

30-32 weeks PMA it is mainly Trace Discontinu with IBIs <15s. From 34 weeks PMA Trave Discontinu evolves into Trace Alternant, where the IBIs are shorter and the bursts of high voltage activity are higher amp. From 38 weeks PMA Trace Alternant evolves into slow-wave sleep

Question 37

How long do neonates spend between active and quiet sleep?

Answer 37

50/50

Question 38

Trace Discontinu v Trace Alternant

Answer 38

Both occur in quiet sleep 1. Discontinu = IBI attenuation <25mV, <34 weeks PMA 2. Alternant = IBI attenuation >25mV, more mature pattern, 34 weeks PMA onwards before evolving into slow wave sleep (SWS)