My goal was that trainees would not view learning about epilepsy and EEG as another hurdle to overcome before graduating. Together, we offer this simplified collection of epilepsy and EEG basics in a simplified format for trainees and clinicians to take home.
Evaluating a Spell
Seizure Mimickers
- Syncope
- Migraine
- Transient Ischemic Attacks (TIAs)
- Sleep Disorders
- Paroxysmal Movement Disorders (PMD)
- Psychogenic Non-epileptic Events or Seizures (PNES)
Limb-shaking TIAs can be confused with focal motor seizures - Often associated with severe carotid occlusive disease [7]. REM sleep behavior disorder manifests with dream fabrication (often violent) - This can be confused with hypermotoric behavior during a nocturnal frontal.
Definition of Seizure and Epilepsy
Reflex seizures are provoked seizures that meet the criteria for epilepsy because of their persistent and abnormal tendency to have seizures triggered by that stimulus.
Seizure Types and Classification
ILAE 2017 Basic Classification of Seizures Types
Seizures may be "unclassified" due to insufficient information or the inability to place them in other categories. Focal seizure with impaired consciousness (previous complex partial seizure) – Focal to bilateral tonic-clonic seizure (previous secondarily generalized. tonic-clonic seizure).
ILAE 2017 Expanded Classification of Seizures Types
Risk Factors for Epilepsy
Causes of Seizures
- Genetic
- Metabolic
- Structural
- CNS Infections
- Autoimmune Epilepsy
Various Onset within first few months Tonic spasms > focal motor, GTC seizures EEG – continuous suppression burst pattern Most cases are associated with a structural brain abnormality Early myoclonic encephalopathy (EME) [7]ErbB4 Onset within first few months Myoclonic seizures > focal motor, tonic spasm EEG – suppression-burst predominantly during sleep ARXX-linked Affects males Tonic spasms Often associated with lissencephaly, agenesis of corpus callosum Ohtahara syndrome (EIEE) CDKL5 [8]X-linkedOnset within first 3 months Affects predominantly females EEG seizure Early intetonic seizure. Severe hypotonia May have Rett-like features (deceleration of head growth, stereotypies) Most develop epileptic spasms Ohtahara syndrome (EIEE) STXBP1VariousTonic seizures, epileptic spasms or tonic-clonic seizures Ohtahara syndrome (EIEE) Epilepsy syndromes associated with febrile convulsions) 2.4 Causes of seizures . Many metabolic epilepsies (Table 2.2) are considered epileptic encephalopathies, where the epileptic activity itself can contribute to severe cognitive and behavioral impairments beyond what can be expected from the underlying pathology alone, and that these can worsen over time [12 ].
Diagnosis of Epilepsy
Neuroimaging and Epilepsy
CT Imaging
MRI
Subtle asymmetric T2 hyperintensity with blurring of the gray-white differentiation and associated deep sulcus involving the left precentral gyrus suggests focal cortical dysplasia. Note dilatation of the left lateral ventricle (ex-vacuo hydrocephalus) due to brain atrophy.
Other Imaging and Workup Prior to Epilepsy Surgery
Memory is similarly tested by showing the patient several different items or pictures and then assessing their ability to recall items after the effect of amobarbital wears off. Can be used to localize sensorimotor cortex; however, mapping via direct cortical stimulation remains gold standard.
Sleep and Epilepsy
Excessive daytime sleepiness (EDS), insomnia and poor sleep quality are common in patients with epilepsy. The prevalence of OSA is higher in patients with epilepsy; approximately 33% of adults with epilepsy have OSA [52, 53].
Sudden Unexpected Death in Epilepsy (SUDEP)
For patients who continue to experience GTC seizures, clinicians should continue to actively administer therapies to reduce seizure and SUDEP risk. For patients with frequent GTC seizures and nocturnal seizures, clinicians may advise, if permitted by their individualized epilepsy and psychosocial circumstances, to use nocturnal monitoring or other nocturnal precautions, such as the use of a remote listening device, to reduce SUDEP risk.
Driving and Epilepsy
Commercial Driving
Aircraft Pilots
Effect of positive airway pressure therapy on seizure control in patients with epilepsy and obstructive sleep apnea. Identification and treatment of obstructive sleep apnea in adults and children with epilepsy: a prospective pilot study.
Choosing Seizure Medications
Antiepileptic Drugs (AEDs)
When to Start Seizure Medication?
This means that if we do not start seizure medications, there is a 66% chance that the patient will not have another unprovoked seizure.
Broad-Spectrum AEDs Used in Generalized Epilepsy
AEDs Used for Focal Onset Epilepsy
AEDs Requiring Bloodwork/Therapeutic Drug
AEDs with Serious Adverse Reactions
AEDs with IV Formulation
AEDs: Metabolic and Elimination Pathways
Individual AED Summaries
Mechanism of action – Na+ channel inhibitor; likely has other mechanisms given its broad-spectrum efficacy. Mechanism of action – Na+ channel inhibitor, likely has other mechanisms given its broad spectrum efficacy. Adverse effects – GI inflammation, anorexia, N/V (improved with extended-release preparation), thrombocytopenia, alopecia, weight gain, polycystic ovaries in women, peripheral edema, tremors, drowsiness, confusion; rare life-threatening pancreatitis and hepatotoxicity (↑ risk with polytherapy and young age; avoid if <3 years old).
Definition and Treatment of Status Epilepticus (SE)
Refractory SE – status epilepticus that persists despite appropriate treatment with first-line (benzodiazepines) and second-line (IV AEDs) medications – Superrefractory SE – “status epilepticus that persists 24 hours or more after. Appropriate treatment of SE (Fig. 3.3) should be started immediately and reduces both morbidity and mortality [22] May be considered if a lesion is identified as the etiology of SE – IV pyridoxine 180–300 mg/d may be tried in young children.
Treatment of Specific Epilepsy Syndromes
GTC seizures usually occur 2–3 years after the onset of myoclonic seizures – myoclonic seizures may occur just before GTC seizures. Because of its teratogenicity, VPA should not be used as a first-line drug in women of childbearing potential. First-line therapy in young women includes levetiracetam and lamotrigine – clonazepam can be used with LTG for myoclonic seizures – combination therapy should be considered after failure of two AEDs.
Stimulation Devices
Vagus Nerve Stimulation (VNS)
Avoid VPA in mitochondrial disorders and in patients with POLG1 mutations due to ↑ risk of hepatotoxicity. The pulse generator is placed subcutaneously in the left chest with a lead attached to the left vagus nerve. 64% of all generalized seizures and 71% of focal seizures are associated with ictal tachycardia or significant ↑ in HR [56].
Responsive Neurostimulation (RNS)
Up to four leads (any depth/subdural combination) can be placed, but only two can be connected to the neurostimulator. The neurostimulator (solid arrow) is connected to a depth plug (dashed arrow) and a cortical strip plug (open arrowhead).
Deep Brain Stimulation (DBS)
Diet Therapy
Ketogenic Diet (KD)
In children with >50% seizure reduction, KD is usually discontinued after 2 years (exceptions: GLUT-1, PDHD). 80% of children who were seizure-free on KD will remain seizure-free after discontinuation of KD [73].
Modified Atkins Diet (MAD)
Epilepsy Surgery
Presurgical Evaluation
Epileptogenic zone – area that generates epileptic seizures and whose removal or disconnection is necessary for freedom from seizures. If seizure localization or lateralization is not possible, Phase II (intracranial) monitoring may be indicated. Rey-Osterrieth Complex Figure Test – Copy Trial Beery-Buktenica Developmental Test of Visual-Motor Integration.
Surgical Diagnostic Procedures
Surgical Treatment Procedures
Definition of Catamenial Epilepsy
Patterns of Catamenial Epilepsy
Diagnosis of Catamenial Epilepsy
Mechanism of Catamenial Epilepsy
Brain Regulation of Sex Hormones
Reproductive Effects of Seizures
Reproductive Effects of Seizure Medications
Treatment of Catamenial Epilepsy
Contraception in Women with Epilepsy
Interactions of AEDs and Hormonal Contraception
Pregnancy in Women with Epilepsy
Pregnancy and Perinatal Counseling
Frequent maternal tonic-clonic seizures during pregnancy have been associated with lower verbal IQ in WWE offspring [36]. Folic acid supplementation is associated with higher IQ in children exposed to AEDs in utero [44]. For women taking VPA, CBZ, PB, PHT and PRM, a higher dose of folic acid 4-5 mg daily may be considered.
Perimenopause and Menopause
5 mg folic acid daily in women without epilepsy provides 85% protection against neural tube defects (systematic review [46]). Current practice is to encourage breastfeeding in women with epilepsy who took AEDs during pregnancy. In the NEAD study, breastfed children exposed to AEDs showed higher IQ and improved verbal abilities compared to AED-exposed children who were not breastfed [40].
Bone Health
Practice parameters update: management issues for women with epilepsy - focus on pregnancy (an evidence-based review): obstetric complications and change in seizure frequency: report of the Quality Standards Subcommittee and the Therapeutics and Technology Assessment Subcommittee of the American Academy of Neurology and the American Epilepsy Society. Association of maternal use of folic acid and multivitamin supplements before and during pregnancy with risk of autism spectrum disorder in offspring. New perspective on the impact of folic acid supplementation during pregnancy on neurodevelopment/autism in offspring – a systematic review.
EEG
EEG Activity
Postsynaptic potentials are the alternation between the excitatory postsynaptic potential (EPSPs) and inhibitory postsynaptic potentials (IPSPs) in the apical dendrites of neurons.
EEG Recording
Application of Electrodes Based on 10–20 System
The circumference of the brain is measured across the occipital, temporal and fronto-polar points (O, T3, T4, Fpz). Fp1 and Fp2 are marked with 5% of the above distance to the left and right respectively.
Modified 10–20 System
Additional Electrodes
Common EEG Montages
If the electrode in input 1 is more negative than the electrode in input 2, the waveform deflection is upward. The same electrode is used in input 2 of each amplifier (Fig. 5.7 and 5.8) – The reference must be carefully chosen, so it is inactive and not contaminated. In reference montage, the amplitude of the waveform (not phase reversal) determines localization of epileptiform abnormality.
EEG Filters/Paper Speed/Impedance/Sensitivity
Odd numbered electrodes are on the left, and even numbers are on the right with "z" indicating midline.
Basic Waveforms of EEG
It also weakens with mental activity, auditory and tactile stimuli - Alpha is increased by closing the eyes and relaxing. The right posterior hemisphere can have up to 20% higher alpha amplitude compared to the left (normal). Normal in young children and during sleep in adults EEG - Normal in young adults in fronto-central areas.
Other Normal Waveforms in the Awake State
Decreased with eye closure, dim lighting, or having someone look at a blank screen - Enhanced by increased complexity of the visual stimulus, rapid gaze shifting,. If alpha does not attenuate to eye opening on one side (Bancoud's phenomenon), there is an abnormality on the non-attenuating side.
Hyperventilation (HV)
The slow activity may begin gradually or abruptly and is more prominent in children.
Photic Stimulation (PS)
Normal Sleep EEG
- Non-REM Sleep: Stages N1, N2, N3
- REM Sleep: 20–25%
- Drowsiness and Stage N1 Non-REM Sleep
- Stage N2 Non-REM Sleep
- Stage N3 Non-REM Sleep
- REM Sleep (Stage R)
Seen in frontal and central leads in short bursts – Concurrent with or following rapid eye movements. In infants, REM sleep accounts for 50% of sleep (called active sleep) and the remaining 50% is non-REM sleep (quiet sleep). By age 2 years, sleep cycle duration is comparable to adults with 75% non-REM and 25% REM sleep.
Benign EEG Variants
Benign Spiky Variants
- Small Sharp Spikes (SSS)
- Wicket Spikes (Wicket Waves)
- Breach Rhythm
Alternation between left and right temporal lobes, but may be more common on one side (Figure 7.4). Wicket spikes do not have after the incoming slow wave - they do not interfere with the EEG background. Note the alternating left and right cortical undulations, greatest in the anterior and middle temporal regions.
Rhythmic Benign EEG Variants
- Rhythmic Temporal Theta of Drowsiness (RTTD)
- Subclinical Rhythmic Electrographic Discharge
Bursts alternate between left and right temporal regions, but may have a field to adjacent parasagittal area. Seen mostly in adults >50 years of age and awake, but may continue to drowsy and sleep. Wicket spikes, temporal, >50 years old, drowsy and light sleep > awake – Break the rhythm over a cranial defect.
EEG Artifacts
Nonphysiologic Artifact Sources
- Electrodes and EEG Equipment Artifacts
- Environment-Related Artifacts
If you are in one or two channels, reuse the affected electrode or try a new connector. If you are in all channels, reattach the ground or reference electrode and turn off lights or other equipment in the room. Note also the 60 Hz fuzzy artifact shown in the blue box, which is the result of high impedance in the T5 electrode.
Physiologic Artifact Sources
Loose electrodes, high impedance electrodes, 60 Hz artifacts, bed movements, electronics connected in the room, and equipment attached to the patient or around the patient.
Epileptiform Discharges
Generalized Epileptiform Patterns
- Atypical spike and wave (>3 Hz)
- Slow spike and wave (<3 Hz)
- Paroxysmal or rhythmic fast activity
- Hypsarrhythmia
The interictal EEG may be normal or abnormal depending on the patient's underlying condition. Syndromes of childhood epilepsy such as Lennox-Gastaut syndrome (Fig. 9.6) – Psychomotor retardation and developmental delay. He showed sudden eye widening accompanied by subtle body tension and facial flushing/grimacing during the above period of generalized rhythmic rapid activity on EEG.
Focal Epileptiform Patterns
- Occipital Spikes
- Central-Temporal (CT, Rolandic-Sylvian) Spikes
- Anterior Temporal Spikes
- Frontal Spikes
- Midline Spikes
- Periodic Lateralized Epileptiform Discharges (PLEDs)
Epileptiform discharges are seen mainly in the central and middle temporal electrodes (C3, C4, T3, T4) originating from the Rolandic region (Fig. 9.12). It can cause seizures that include lower limb seizures, atonic seizures, and supplementary motor area (SMA) seizures [1] (Figure 9.17). If PLEDs are associated with intermittent rhythmic discharges, the term PLED Plus is used (Figure 9.19).
From Spikes to Seizures
- Electrographic Seizures
Seconds later, he experienced arrest of speech and right facial twitches with EEG showing developing focal electrographic seizure (see Fig. 9.20). This correlated with the patient's clinical seizures beginning with flushing of her face and cycling leg movements. PLEDs pattern is interictal, but if associated with intermittent rhythmic activity (PLEDs Plus), it indicates impending focal seizures.
Four EEG Patterns in Encephalopathies
- Slow Wave Patterns
- Epileptiform Patterns
- Periodic Patterns
- Coma Patterns
Bursts of spikes and sharp waves or mixed frequency activity followed by intervals of relative weakening of activity (Fig. 10.11). The bursts become less frequent as the brain loses more function and the suppression becomes longer (Fig. 10.13). Commonly elicited by alarming stimulation of the patient (Figs. 10.14 and 10.15) – Probably due to dysregulation of thalamo-cortical pathways in an abnormal and.
Prognosis of Coma Based on EEG
Brain Death and Electrocerebral Silence
