EEG Flashcards
Introduce EEF and neurophysiology as a clinical sub-speciality
Be able to explain the process of obtaining a routine EEG to a patient
Understand the role of EEG in the investigation of patients
Appreciate basic background wave forms and pathological features
What is EEG
Now a routine clinical test, in which brain electrical activity is measured in order to make inferences about brain health.
Ask the patient to relax and then perform some stimulatory procedures.
Electrode placement in EEG
Has been standardised so that results are comparable.
Placed in a 10-20 formation.
CZ electrode is the intersection point between coronal plane (preauricular points either side) and sagittal side (nasium to mid-point occipital protuberance). All others placed in relation to this point.
Capital letter- reflects brain lobe or region (F- frontal, O- occipital, C- central regions)
Lower case numbers odd- left hemisphere
Even numbers- right hemisphere reason
P- front or polar
Z- midline
What is measured in EEG
Recording summative electrical activity from the cortex.
Cortex arranged into 6 different layers- mixture of excitatory and inhibitory layers- organised into columns by thalamic inputs.
Activity from columns- multiple cells working together
Differential amplifiers
Magnifies the voltage input between two input materials
Subtracts the common components in signals and amplifies resulting outcomes
Useful in biologic systems
Detects small differences between inputs
Montage
Reflects the way that the electrodes are in position in relation to each other
e.g., transverse montage
What do green markers represent
what do red markers represent
green- time
red- added by technician– eyes opening, hypertension
what would eeg look like if input 1 was negative with repsct to input 2?
And 1 positive in respect to 2?
patient factors to cpnsider when doing an eeg?
age
clinical state- drowsy, drugged
montage
wave forms
4 differnt rhyhtms
Rhythm
Frequency (Hz)
Amplitude (uv)
Recording & Location
Alpha (α)
8-13
50-100
Adults, rest, eyes closed, occipital region
Beta (β)
14-30
20
Adult, mental activity, frontal region
Theta (θ)
5-7
>50
Children, drowsy adult, emotional distress, occipital
Delta (δ)
2-4
>50
Children in sleep
who would you expect the differnt rhythms in?
alpha- normal for adults at rest- prominent on occipital- disappears w open eyes
beta- faster and lower amplitude- concentrating, medication -frontal regions
theta- slower agin- children and deep sleep
What is this a classic presentation of?
- 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.
seizure
after someone has a seizure its important to think of what
why it has happened- exclude serious things like brain tumour, previous fit
understanf risk of reoccurence- MRI and EEG
prognostic index- 1 disability
epileptic activity (epileptiform discharges)
- Characteristic EEG waveforms typically seen in persons with epilepsy
- Typically looking for inter-ictal epileptiform discharges (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.
what are sharp waves
spikes
spike and waves
polyspike
Name
Definition
Sharp waves
Transient with a pointed peak and duration of 70-200ms
Spike
Transient with a pointed peak and duration of 20-70ms
Spike and wave
Spike followed by slow wave
Polyspike
Transient with multiple spikes
provocation methods
Hyperventilation- useful in certain childhood epilepsies
Photic stimulation- fast frequencies e.g. light
seizure classifications
- Focal onset
- Generalized onset
- Unknown onset
Generalised
Seizures originating within bilaterally distributed networks
1) absence- periods of vacancy
2) myoclonic- brief jkerk mocements upper limbs
3) atonic- postural control gone
4) tonic- limbs stiffening
5) clonic- seizures
6) tonic-clonic- stiffening followed for jerking
Characterized by generalized discharges
focal seizures
involve unilateral networks
can be excised if tracked
phase reversal
Draws attention to localised differences in potential between nearby electrodes.
status epilepticus
Status epilepticus
Continuous seizure activity for >5-30 mins
Urgent medical condition
Convulsive status epilepticus
Obvious motor features
Clinical diagnosis – no EEG required (usually)
non-convulsive status epilepticus
No obvious motor features
Confusion/Altered consciousness
Consider in patient with epilepsy.
EEG
what is videolemetry
Contiguously monitored with EEG and video
1) diagnose difficult seizure types
2) Understand where in the brain seizures are coming from — think focal – allows for surgery
this history
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
prion disease- rare- neurodegenerative
narcolepsy
multiple sleep latency test (MSLT)
Tetrad for diagnosis
- daytime sleepiness
- Cataplexy- sudden, brief loss of voluntary muscle tone triggered by strong emotions such as laughter
- sleep paralysis
- hypnagogic/hypnopompic hallucination
Multiple Sleep Latency Test (MSLT)
- 5 separate EEG recordings
- Dark, quiet room
- Sleep latency usually 10-20mins
- Abnormal mean latency <8mins
- SOREMP on minimum 2 occasions
