EEG Interpretation Flashcards
What are two components to examining EEG?
▪️ Background (ongoing activity)
▪️ Transients (brief spikes)
What can you look for in the background EEG signal?
▪️ Whether it is normal for their age/state (e.g., conscious, stage of sleep etc)
▪️ If it is abnormal, is it generalised across channels/bilateral, or is it focal?
What is the main distinction to make when examining transients?
Whether it is cerebral or not (i.e. an artefact)
What are the three distinctions to make when looking at cerebral transients?
- Normal for age/state
- Nonspecific
- Epileptiform (benign or significant)
What distinctions need to be made when examining epileptiform transients?
▪️ Generalised vs focal
▪️ Interictal vs ictal
What are interictal epileptiform discharges?
▪️ Paroxysmal activity clearly distinguished from the background
▪️ Abrupt change in polarity occurring during several milliseconds
▪️ Duration less than 200ms
▪️ Must have physiologic field (not an artefact)
What is upgoing EEG activity (e.g., height of spike)?
Negative
How do interictal epileptiform discharges appear on EEG?
Spike and wave patterns
▪️ Spike <70ms
▪️ Sharp waves 70-200ms
▪️ Can be generalised spike and wave, polyspike and wave, or slow spike and wave
What is PLED?
Periodic lateralised epileptiform discharges
(IED with repetitive spikes and waves, usually more associated with acute conditions such as HSV encephalitis than epilepsy but can still be associated with seizures)
What are the features of ictal activity in focal epilepsy?
▪️ Change in amplitude
▪️ Change in frequency
▪️ Propagation (spread) - reflects pathophysiology of seizures
▪️ EEG onset and offset
Typically, what does one bar on EEG represent?
One second
What is the hallmark EEG sign of absence epilepsy?
3-4 spikes per second (3-4Hz), generalised across channels
What is the specificity of a measure?
The true negative rate - the proportion of healthy subjects who do not have the sign
What is the sensitivity of a measure?
The true positive rate - the proportion of patients who show the sign
How long is a routine EEG recording?
20 minutes
What is the sensitivity and specificity of the first EEG?
▪️ 40% sensitivity
▪️ >96% specificity - very few without epilepsy will show something
How do we improve EEG sensitivity for epilepsy?
▪️ Repeat EEG - more likely then to see something that occurs randomly
▪️ Sleep EEG - increased rate of discharges, particularly in stage 2 sleep
(improves from 40% to 80-90%)
What is the main strength of an EEG for detecting epilepsy?
On the first trial, you are very unlikely to see abnormal discharges in people who don’t have epilepsy
Does IED/spikes always indicate epilepy?
No!
May be present in healthy people as well as various conditions such as neurodegeneration or when on psychotropic medication
Why is the false positive rate of spikes in EEG slightly higher in children?
▪️ Rolandic spikes (genetic phenomenon)
▪️ Asymptomatic siblings of those with rolandic epilepsy may show them but grow out of it
What are the main EEG recording modalities available for clinical investigation?
▪️ Routine and sleep VEEG
▪️ Ambulatory EEG
▪️ Polysomnographies (incl other components)
▪️ Electro-corticogram (EcoG) - mats over brain during surgery to determine function and delineate pathology
▪️ In-patient video-telemetry and home VT
What is video-telemetry?
Continuous video-EEG monitoring to record seizures
How long is hospital admission typically for inpatient VT?
3-5 days
(up to 3 weeks with implanted electrodes)
What are the four types of VT available?
▪️ Inpatient VT
▪️ Home VT (HVT)
▪️ Mobile (ambulatory) HVT
▪️ Cloud based HVT
What are the two components of VT assessment?
▪️ EEG activity (interictal, ictal, postictal)
▪️ Semiology (behavioural changes)
What are the two main components of semiology examination?
▪️ Ictal assessment (check response, memory, ability to move and speak etc)
▪️ Signs
What information can you get from the semiology signs using VT?
▪️ Evolution of the seizure
▪️ Lateralisation
▪️ Localisation
Is EEG needed for the diagnosis/definition of epilepsy?
No!
What is EEG used for in epilepsy?
The CLASSIFICATION (focal vs generalised, idiopathic vs symptomatic)
How many unprovoked seizures are necessary for diagnosis and treatment of epilepsy?
Two
What are generalised polyspike waves a typically sign of?
Juvenile myoclonic epilepsy
Does interictal EEG prove the presence of epilepsy?
No! - some spikes seen in other conditions
Does a normal EEG exclude epilepsy?
No! - low sensitivity during first recording (60% will show up normal)
What is the most common form of reflect epilepsy?
Photosensitive epilepsy
What are the three main indicators of photosensitive epilepsy following intermittent photic stimulation?
- Photic following at flash rate
- Photic following at harmonics
- Orbito-frontal photo-myoclonia
Photosensitivity is a ________________ and refers to patients with ___________________
▪️ EEG marker
▪️ Reflex epilepsy
What are the main types of photosensitivity syndromes?
▪️ Pure photosensitive epilepsy (seizures only in response to light flashes)
▪️ Epilepsy with photosensitivity (58%)
▪️ Photosensitivity without epilepsy (may be genetic marker)
What form of idiopathic generalised epilepsy is most commonly associated with photosensitivity?
Juvenile myoclonic epilepsy (JME) - 30%
(Followed by childhood absence epilepsy and GTCS on awakening)
How can video EEG telemetry be used for presurgical evaluation in epilepsy?
Can help with other measures to determine the epileptogenic zone to be removed (and whether it can be removed without deficits)
▪️ Interictal EEG - indicate irritative zone
▪️ Ictal EEG - indicate ictal onset zone
What are the two main contacts measured by an implanted electrode for EEG?
▪️ EP = entry point
▪️ T = target (1) - inner aspect
(can have more contacts in between)
When is alpha activity seen on EEG?
On eye closure
(Responsive but relaxed)
What is the main EEG sign of dissociative seizure?
Alpha activity but unresponsive
What is the activation procedure for NES?
Suggestion with non-epileptic stimulation approach that cannot commonly induce epileptic discharges/seizures
Sometimes with hyperventilation
What happens during activation clinic?
- 30 minute EEG obtained
- History including witness account
- Activation procedure
- Event reviewed by witness
- Diagnosis not typically discussed
How can EEG be used for diagnosis of non-epileptic/dissociative seizures?
Activation clinic
What are the two important clinical components of consciousness and how can we determine these in disorder of consciousness?
▪️ Awareness - do they have memory of the event (e.g., seizure)?
▪️ Responsiveness - ask a witness whether they were able to respond (e.g., during the seizure)
What disorders/states of consciousness can EEG be useful for?
▪️ Coma
▪️ Sleep
▪️ Wakefulness
▪️ Seizures
▪️ Parasomnias
▪️ General anaesthesia
▪️ Locked in syndrome
▪️ Non-epileptic seizures (but complicated balance of awareness/responsiveness)
What disorders/states of consciousness does EEG struggle with?
▪️ Minimal consciousness - can look almost normal
▪️ Dementias
▪️ Vegetative state
When is alpha generated?
On eye closure
What can you conclude if someone is not reaching alpha (theta instead)?
They are drowsy
What does alpha on eye opening and eye closure indicate?
An arousal response
(Following drowsiness/theta)
What are Stimulus-induced, period, rhythmic, or ictal discharges (SIRPID) important for?
▪️ Determining ictal interictal continuum (seizure activity)
▪️ Differential diagnosis in status epilepticus
▪️ Prognosis of poor outcome after cardiac arrest (in unresponsive patients)
What does more slow EEG indicate?
More severe abnormality/encephalopathy
What are the main indicators of more severe abnormality?
▪️ Slower activity
▪️ Less reactive
▪️ Less sleep architecture
What is are main differential diagnosis for slower and less reactive EEG?
▪️ Drowsiness
▪️ Drugs
