Clinicians guide to EEG-electroencephalogram Flashcards
History of EEG
The first human EEG recording was obtained by Hans Berger in 1924. The upper signal is EEG and the lower is a 10Hz timing signal.
Hans Berger, the first person to record EEG brainwaves in humans
WHere to place electrodes in EEG
Standardised so results across different trust can compare
One important tone - CZ (intersection point between the coronal plane and sagittal plane). All other electrodes placed in relation to this
EEG process
- Physiologists conduct the process and the medically trained neurophysiologists interpret the results.
- Noninvasive, pain-free. 20-30mins in total
Layers cortex - neuropathologically defined (neuroexcitatory and inhibitor neurons working together).
Where electrical activity comes from in EEG - Electrical activity from summated electrical activity from cortex.
Differential Amplifiers
- Magnifies the voltage input - so you can read output easier
- Subtracts the common components in signals between 2 inputs and amplifies this
- Useful in biological systems - can detect small differences between 2 inputs
Montage
- Reflects way electrodes are all connected and referenced to each other and then displayed on screen
- Eg - there are 2 common ways - longitudinal bipolar montage and horizontal bipolar montage. We are taking electrodes in standardized electrodes and sign them as input 1 and 2 to get different EEG channels.
- F3 input 1, compare to C3 and have second EEG channel F3C3. DO same on right side brain etc
Longitudinal Bipolar montage on EEG
Multiple channels reflecting difference between electrodes
Green - second markers
Red markers - added by technician added.
Downside - reference in montage. Compare leads and then down lateral and downsides and up the middle.
Difference in ptoential between 2 points
Transvere bipolar montage
Input lead I negative in respect to Lead 2 then up deflection
Downward reflection then lead i positive in relation to lead 2
EEG Interpretation
- Age of patient
- CLinical state of patient - awake, drowsy, asleep
- Montage
- Wave forms - how many squiggles in each 1 second (frequency)
SO we know background normal rhythm
Alpha - normal in adults resting partiuclarly over occipital region
Beta rhythms - fast with lower amplitude - normal in adults if ocncentrating
Theta and delta can be normal in children and sleep but not if patient awake etc.
Waves in EEG
Rhythm
Alpha rhythm
WHat rhythm eeg
1-2 waveforms, high amplitude, slow activity widespread across EEG
Generlaised delta acitvity and worrying in right circumstances
- 20 Male
- Collapsed without warning
- Witnessed to become stiff, and then started jerking. Foaming at mouth, and became cyanosed. Breathing pattern changed. Incontinent of urine.
- Lasted 2 minutes
- Recovered slowly over 30 minutes, and was confused afterwards.
- Headache, tongue biting.
- Typical history of seizure - commonly presenting complaint
- WHen presents like this - invetsigate why happened and risk of it happening again.
- WHy - exclude tumours, previous strokes (so do MRI),r equest EEG (check risk seizure occurring again rather than diagnose here)
- First fits common
Prediction risk seizure recurrence after single seizure and early epilepsy
- Single seizure - prognostic index 0
- identified if had 2+ seizure sbefor epresentation then prognostic index 1/2
- Neurologicla disorder - 1
- Abnormal EEG - 1
- Combine to risk classification group.
- Low risk - only one seizure and normla mRI and EEG (0 score). 1 in 5 had further seizure, 1 in 4 by 3 years and 1 in 3 by 5years without treatment. No anticvoulsant with normal EEG here
Study 1500 patioents
Epileptic Activity (‘Epileptiform discharges’)
- Characteristic EEG waveforms typically seen in persons with epilepsy
- Typically looking for inter-ictal epileptiformdischarges (IEDs): asymptomatic epileptic abnormalities occurring between seizures
- Ictal = epileptic discharge producing clinical seizure
- Spikes or sharp waves, superimposed on background rhythms
- Localised versus generalised patterns : essential role in classifying the type of seizure disorder.
Looking on EEG to rule epilepsy out etc.
Want them seen in those at risk EPilep[sy but not seen in those not at risk.
Provocation methods in routine EEG - everyone will undergo these emthods
- Hyperventilation (in children often get them to blow round windmill)
- Photic stimulation - some people can have normal change in EEG in repsonse but some get epileptic discharges)
- Sleep deprivation 30% - thought to increase diagnostic yield about 30%
- 23 Female
- Two tonic-clonic seizures (stiff, collapse, synchronous limb jerking)
- Clinical diagnosis of epilepsy made.
- Started anti-convulsant treatment in clinic.
- EEG requested…
EEG used to classify type epilepsy not risk reccurrence
Seizure classification
Sognfiociant management implications - eg if surgery option
We want to know if:
- Focal onset
- Generlaised
- Unknown - dont knwo clinically or on ecg
Generalised seizures -
Seizurea originating within bilaterally distributed networks:
- Absence
- mYOCLONIC
- atonic - loose postural control
- tONIC -limb stiffening no jerking
- Clonic
- Tonic - clonc - stiffening onset then jerking
Typical spike wave discharge
Cant tell where started as synchronous - often feature generalised epilepsies
Focal seizures
Can retain awareness - suggest motor cortex onset abnormal activity
Unusual aurus sense somethign ocming over them, funny taste/smell etc and loose awareness - tpyical tempiral berve onset seixure
Focal can also become generalised - appear to progress to tonic clonic seizure
Left hand side brain - looking lateral aspect
See normal brain rhythms on left side but on right side we have build up high amplitude rhythmic acitvity which is focal and localised on that area brain
Sharp transient, localised over left hemisphere
Phase reversal in EEG
Where abnormal signal might be coming from
Draws attention to localised differences in potential between nearby electrodes
- 2 electrodes equal in charge so flat line.
F3-C3 = f3 more positive so down line
F3-P3 = F3 more negative so up line
2 lines pointing at each other is phase reversal - can be helpful as you start thinking. Drawining eye in to area of C3
SHow on ECG phase reversal
Down and up reflection
Draw eyes in to T6 to look at it and might correlate with imagign findigns
- 66 Female
- History of epilepsy with tonic-clonic seizures
- Good usual functioning status
- Admitted to hospital with another episodes of acute confusion
- Awake and mobile without limb deficit or evidence of abnormal movement
- Following people
- Reduced speech content: ‘yes’, ‘yes’, ‘yes’
- Purposeless wandering, often not fully clothed
- Tended to improve spontaneously after 4 hours
EEG - in this state. 3Hz spike wave discharge which is generalised across whole EEG so essentially in status epilepticus
Status epilepticus
convulsive SE- is medical emergency and usually clinical diagnosis not on EEG
Non convulsive - remember if confused consider this.EEG can be very useful. Treatment -c hange smedication but usually not as urgent as convulsive SE
Advanced EEG technique - When patient come in and admitted for period up to 2weeks and continuosuly monitered with EEG with video footage. Used for:
- Diganose difficult to diagnose seizure types
- Understand where in brain the seizure is arising
Particulary if chance of focal epilepsy if might be the possibility of surgery to get seizure control.
Surface EEG - causing electrical potentials through scalp and scull reduces sensitivity so when thinking baout taking focal resection where seizure starting not spreading so need to monitor areas more refined
- 30 Female
- Explosive onset of seizures – up to 20 per day
- Often wax and wane
- No tongue biting or incontinence
- Recovery rapid
Wax and wane - looks like stopping then comes back again
Cna have dissociation not epilepsy
- 47 Female
- Usually fit and well, hairdresser
- 4 week history of progressive difficulty walking with falls, attending clinic in a wheelchair. Confusion, deferring to family to provide history. Brief jumping movements noted.
- On examination: cognitive impairment with poor memory, ataxia and myoclonic jerks
- Not seizure but EEG useful.
- Corncerning hsitory but makes oyu think of Prion disease -
- Group of rare, uniformly fatal neurodegenerative diseases.
- Sporadic (85-90%); Genetic (10-15%) and acquired (<1%).
Prion disease
Example criteria
Typical EEG: generalised triphasic periodic complexes, at approx 1/second; slow background
Generlaised triphasic periodic complexes
In right clinicla circumstances cna help to diagnose with prion disease
- 23 Male
- Presents with excessive daytime sleepiness
- Falls asleep frequently
- Collapses to the floor with heightened emotion, eglaughing
- Brief inability to speak or move on waking
- Vivid dreaming as falling asleep
Rare - narcolepisy (not this but think of this from sleepy in day)
EEG useful - changes massively in normal sleep
Uses EEG
An electroencephalogram (EEG) is a noninvasive test that records electrical patterns in your brain. The test is used to help diagnose conditions such as seizures, epilepsy, head injuries, dizziness, headaches, brain tumors and sleeping problems. It can also be used to confirm brain death.
Narcolepsy
Cna usage normal sleep EEG and apply to things like narcolepsy
(Test can help check treatment working)?
Summary EEG
- EEG is an established, routine test used in clinical practice
- Non-invasive, painless test
- Provides essential information for patient management
