Response to sensory disturbances - flashing checkboard pattern Usually recorded upside down

EEG Flashcards by Maria Sasakis

From what age is EEG recordable?

22 weeks of gestation

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Is there a standard EEG for all stages of development?

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What are the types of EEG?

Routine awake portable

Sleep (natural, sleep deprived, drug induced)

Ambulatory

Video telemetry - long term recording

Back averaging

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What are evoked potentials?

They are EEG traces recorded in response to sensory disturbances

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What are the types of evoked potentials?

Visual evoked potential

Sensory evoked potential

Motor evoked potential

Brainstem evoked potential

Electroretinogram and electrooculograms

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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

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When do we use video telemetry?

Used when contemplating epilepsy surgery

Less for diagnostics

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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

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What medication is used in paediatric patients to induce sleep?

Melatonin

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What is a VEP?

Response to sensory disturbances

flashing checkboard pattern

Usually recorded upside down

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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

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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

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What do we see in the SEP of an MS patient?

SEP is slowed

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What are motor evoked potentials?

Cortical magnetic stimulation –> check time for arm to twitch

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When are MEPs used?

Spinal cord surgery

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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

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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

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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

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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

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What are EEG electrodes made of?

Ag-AgCl in a state of equilibrium

AgCl- + e- = Ag + Cl-

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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