EEG Flashcards
From what age is EEG recordable?
22 weeks of gestation
Is there a standard EEG for all stages of development?
No
What are the types of EEG?
Routine awake portable
Sleep (natural, sleep deprived, drug induced)
Ambulatory
Video telemetry - long term recording
Back averaging
What are evoked potentials?
They are EEG traces recorded in response to sensory disturbances
What are the types of evoked potentials?
Visual evoked potential
Sensory evoked potential
Motor evoked potential
Brainstem evoked potential
Electroretinogram and electrooculograms
When do we do ambulatory EEGs?
When is doubt over whether they are having seizures or you want to find out seizure frequency
Good for ruling out non-epileptic attacks
When do we use video telemetry?
Used when contemplating epilepsy surgery
Less for diagnostics
What is back averaging?
Frequent epileptiform activity can be associated with twitch. You might miss one spike from myoclonus.
So you measure with EEG and average the areas showing the twitch to remove background noise
Enhances abnormality
What medication is used in paediatric patients to induce sleep?
Melatonin
What is a VEP?
Response to sensory disturbances
- flashing checkboard pattern
Usually recorded upside down
What do we see in the VEP of MS patients?
Delayed response to visual stimulus
- P100 is delayed if there is an optic nerve problem
Give an example of how an SEP would work
Sensory disturbance in foot or arm
Stimulate with electricity and then measure CNS response - see if it is normal
What do we see in the SEP of an MS patient?
SEP is slowed
What are motor evoked potentials?
Cortical magnetic stimulation –> check time for arm to twitch
When are MEPs used?
Spinal cord surgery
What is the 10/20 system?
23 electrodes placed symmetrically over the scalp on very specific places according to places in the cortex underneath
10 and 20 refer to distance between certain places in head
How do you conduct an EEG?
- Skin is prepared and electrodes are held in place with conductive paste
- Locations are measured and marked according to the international 10-20 system
- Recording for ~20 min with periods of eye opening and closing
How do monopolar measurements differ from the EEG montage we use?
Unlike the 20/10 system, it utilizes one electrode at e.g. the ear and the potential from that electrode to some another electrode often far away is measured
What does an EEG record?
Voltage differences between two points on the scalp over time
The voltage difference is the sum of a mixture of excitatory and inhibitor post-synaptic potentials in ~5cm^2 of the cortical surface
What are EEG electrodes made of?
Ag-AgCl in a state of equilibrium
AgCl- + e- = Ag + Cl-
What do EEG amplifiers do?
Compare the differences in voltage between pairs of electrodes
What are montages?
Different ways EEG electrodes can be connected
What can you do to induce seizure readings?
Hyperventilation - increase slow activity and reduces seizure threshold
Photic stimulation (flashing light - sometimes colour dependent) - normally elicits time locked evoked responses
Sleep: drug induced sleep deprivation
What can be the negative side effects stimulating seizures for EEGs?
Someone who has not had seizures so far can lose drivers licence
Seizure can cause damage
What kind of rhythms do we see in EEGs?
Alpha: 8-12 /sec
Beta: >12/sec
Theta: 4-<8/sec
Delta: <4/sec
What is typical for alpha waves?
Fairly fixed, doesn’t fluctuate in the short term
Sensory stimulus suppresses it so best when eyes are closed
Comes from the thalamus (synchronised thalamocortical activity)
Seen over the occipital regions
What is typical for beta waves?
Usually anterior
Low voltage
Desynchronised
When are beta waves worrisome?
Lots of beta activity commonly seen in benzodiazapine use
Usually nothing pathological
What is typical for theta waves?
Seen widespread but mostly temporal
Acceptable in young adults until 30 and in temporal areas
When are theta waves worrisome?
If you have too many theta waves as an adult
What is normal for delta waves?
Widespread when asleep
When are delta waves worrisome?
Definitely pathological in awake patients
When do you use EEGs?
Diagnostic:
- Evidence of seizure activity
- Seizure classification
- Evidence of status epilepticus
- Focal abnormalities
- Metabolic and infective encephalopathies
- Neurodegenerative diseases, dementia, CJD
- Sleep disorders
- Planning treatment
Monitoring:
- Evidence of drug effects (in US used in operation for sedation)
- Adequate suppression of status epilepticus
Prognostic:
- Checking brain injury
- In coma it is combined SEP
How is status epilepticus different from other epilepsy?
Patients are in a state of epilepsy that isn’t self-limiting and neurotoxic
Why might we need to check if someone has status epilepticus?
People in ICU might not wake up due to brain damage or status epileticus (find out why)
What kind of metabolic/infective encephalopathies can be studied with EEG?
Helpatoencephalopathy
Triphasic waves found in encephalopathies and CJD
What do we see in normal awake EEGs?
If eyes are closed maybe alpha
If child: theta
Some anterior beta
What are the stages of sleep and what are their characteristics?
Stage 1: drowsiness, attenuation of alpha activity, increasing amounts of theta
Stage 2: vertex sharp waves, K complexes, sleep spindles, positive occipital sharp transients of sleep, up to 20% slow and theta activity
Stage 3: 20-50% slow and theta
Stage 4: >50% slow, deep sleep, slow wave sleep(non-REM)
Stage 5: REM
What abnormal patterns would you see in epilepsy?
Focal or generalised
May be continuous (status)
PLEDs (periodic lateralised epileptiform discharges)
What abnormal patterns would you see with drugs?
Activity seems slowed (usually there are many types of patterns)
Fast, beta activity - especially in barbiturates and benzodiazepines
Burst suppression: anaesthetic doses (look quite epileptiform: flat and then bursts)
Epiletiform: Clozapine and Olanzepine
What abnormal patterns would you see with metabolic or toxic issues?
There are slow focal or diffuse patterns
You would expect PLEDs
What abnormal patterns would you see with trauma?
It is slow, focal/generalised
Burst suppression (poor prognosis)
Breach rhythm
What are the causes of EEG abnormalities?
Epilepsy
Drugs
Metabolic/toxic
Trauma
Three types of epileptic EEGs
Inter-ictal
Ictal
Post-ictal
What might you see in an inter-ictal EEG?
Normal in 50% of patients
Might see spike/sharp and slow wave complexes
Cannot exclude epilepsy without inter-ictal EEG
What do you see in ictal EEG?
Usually you see sharp waves or spikes build up in frequency and area of distribution
Can also see attenuation or slowing immediately before or after seizure
What can you see in post-ictal EEG?
Generalised
Suppression/attenuation of activity which may persist for hours or days after a seizure
What suggests a good prognosis in coma?
Mix of frequencies
Reactivity: pain, suction, auditory
Variability of frequency and amplitude
Evolution to more favourable pattern over time
A patient had brain surgery and is now on light sedation but is twitching. What could it be?
A seizure or left over anesthetics
You have to find out which with an EEG
What suggests a bad prognosis in coma (off sedation)?
Monotonous Rhythms (alpha coma)
Lack of reactivity
Low amplitude
Burst suppression
Periodic bilateral spikes, may be associated with myoclonus
What might we use to get accurate localisation of brain issues?
Multiple scalp electrodes (telemetry)
Cortical grids
Depth electrodes
Electrocorticography
PET scanning
fMRI
