EEG and semiology in focal epilepsy Flashcards
Generalized vs focal seizures
Generalized seizures appears to have a bilateral onset as the seizure rapidly involves bilateral networks. Focal seizures arise within networks limited to one hemisphere.
In what percentage of people does scalp EEG fail to lateralize?
25% in patients with unilateral mesiotemporal epilepsy; 33-50% in patients with extratemporal epilepsy
How can focal seizures be divided?
Focal seizures wo impaired awareness w or wo associated motor or autonomic components, involving subjective sensory or psychic phenomenon = simple partial seizures or aura
Focal seizures w impairment of awareness, also called dyscognitive, implying a larger cerebral involvement = complex partial seizures
Secondary generalized seizures, which are focal seizures that evolve to a bilateral convulsive seizures
Dystonic limb posturing
Contralateral
Early head turn
Ipsilateral
Late/versive head turn in transition to generalization
Contralateral
Figure of 4 sign
Contralateral to the tonically extended arm
Todd’s paralysis
Contralateral
Focal clonic activity
Contralateral
Unilateral eye blinking
Ipsilateral
Unilateral limb motor automatisms
Ipsilateral
Postictal nose wiping
Ipsilateral
Preservation of ictal speech
Nondominant temporal lobe
Postictal aphasia
Dominant hemisphere
Ictal speech arrest
Dominant temporal lobe
Ictal vomiting
Nondominant temporal lobe
Hypermotor
Frontal lobe, less commonly insular or even temporal
Ictal urinary urgency
Nondominant temporal lobe
Limb parasthesia
Contralateral parietal lobe
Simple visual hallucinations
Contralateral occipital lobe
Complex visual hallucination
Contralateral temporo-occipital lobe
Temporal lobe seizures
Arise from mesial and lateral temporal regions
The distinction between medial and lateral is important as mesial temporal lobe seizures will be abolished after standard temporal lobectomy or selective amygdalohippocampectomy, while lateral temporal lobe seizures will often require invasive video-EEG monitoring in order to map eloquent cortex and tailor a surgical resection.
Clinical features supporting mesial temporal lobe epilepsy = early age of onset, history of complex febrile seizures, congenital brain malformations, CNS infections, tumors, head trauma, perinatal injury, stuttering course of seizure control, and typically with well-controlled seizures in early childhood but re-emergence of refractory epilepsy in adolescence or early adulthood and frequent or rare secondarily generalized seizures
Clinical seizures favoring lateral temporal lobe epilepsy = later age of onset, absence of early risk factors, absence of hippocampal atrophy, and more commonly negative structural or functional brain imaging
Mesial temporal lobe seizures semiology = often have an aura (rising epigastric discomfort or inappropriate fear or olfactory feeling and/or autonomic signs like pallor, flushing, mydriasis, irregular respiratory or respiratory arrest, abdominal borborygmi, and eructation). These seizures often exhibit contralateral dystonic posturing of the hands (and ipsilateral hand automatisms), preserved ictal language if the focus is in non-dominant temporal lobe, ictal speech arrest if the focus is in dominant temporal lobe, posticttal nose wiping with ipsilateral hand, ictal vomiting or retching behavior, and head version in transition to secondary generalization.
On EEG, mesial tempora lobe seizures are often associated with a rhythmic theta-range ictal rhythm on scalp EEG. Typically, temporal rhythmic activity of <5 Hz frequency is followed wi 30s by 5-7 Hz sphenoidal maximum theta activity. At times, sudden generalized or lateralized suppression or attenuation is also seen. Interictal EEG abnormalities consistently of frequent spike or sharp waves predominantly in the inferomesial (sphenoidal electrodes) and anterior temporal regions.
Lateral temporal lobe seizures etiology = less common than mesial temporal lobe seizures, may be associated an aura of vertigo or with auditory or visual hallucinations. These seizures often evolve early to unilateral clonic activity and early head turn.
On scalp EEG, lateral temporal lobe seizures have a high incidence of repetitive epileptiform discharges at ictal onset. Also if present, a transitional shop wave at ictal onset favors a neocortical>hippocampal seizure onset. Neocortical seizures often start with higher frequency activity (alpha or beta range) on scalp EEG but may also be associated with irregular polymorphic 2-5 Hz lateralized activity. Interictal EEG abnormalities in neocortical temporal epilepsy may be absent or consist of occasional spikes or sharp waves predominant in the anterior or mid-temporal regions.
Features that do not point to mesial vs lateral temporal onsets: ictal emeticus, ictal urinary urge, ictal spitting, which often to the non dominant temporal lobe, and piloerection, which localizes to the dominant temporal lobe
Extratemporal seizures
AKA TPE or temporal plus epilepsies
Can mimic temporal lobe seizures both in terms of semiology and electrographically
Early signs can point to involvement of perisylvian region, OFC, or temporal parieto-occipital junction
Frontal lobe seizures
2nd most common after temporal lobe seizures
Do not always produce LOA and when they do they often have brief or no post-octal period so easy to confuse for PNES, parasomnia, movement disorder, etc.
Characterized by stereotyped appearance, frequent nocturnal occurrence, and brief duration
Can occur in clusters
May present as bizarre attacks that appear hysterical with fencing and posturing, prominent motor automatisms, usually completely, aggressive sexual automatisms with variable complexity
Four groups - SMA, anterior cingulate, OFC, dorsolateral frontal
The ictal EEG often shows excessive generalized muscle artifact at the onset and the ictal discharge is typically brief and delayed. The ictal EEG can also be falsely localized.
The interictal EEG is commonly normal though multifocal epileptiform discharges may be seen in medial frontal lobe seizures. In dorsolateral frontal epilepsy, the interictal EEG may show focal interact epileptiform discharges localizing to the epileptogenic focus. Frontal lobe seizures may also be characterized by bilateral synchronous interictal epileptiform discharges represent secondary bilateral synchrony. Alternatively, focal epileptiform discharges are seen in the ipsilateral or contralateral temporal or frontal lobes.
SMA seizures
May occur without alteration of consciousness of simple partial seizures
Typical features: Prominent tonic posturing, usually of contralateral upper extremity, contraversive head and eye deviation, preservation of consciousness in some patients, and poetical Todd’s paresis
Anterior cingulate seizures
Sudden changes in mood and elaborate gestural frequent tonic/dystonic posturing, rare changes of facial expression of fear, vocalization, complex motor automatisms that are often hypermotor, and autonomic features
Orbitofrontal seizures
Sudden complex gestural automatisms, hyper motor activity, olfactory aura, fear and prominent facia expressions of fear, hallucinations, illusions, and prominent autonomic features
Dorsolateral frontal seizures
Unilateral clonic activity involving facial and spreading to the arm and leg. These seizures often occur without the alteration of consciousness. They often involve ford head turning to the contralateral side with lateral deviation of the eyes indicating activation of the frontal eye field. In dominant frontal lobe convexity seizures, aphasisa is often seen.
Why can parietal and occipital lobe seizures present with temporal or frontal symptomatology?
Because of their spread from their locus of origin and are often the cause of pseudo temporal and pseudofrontal seizures.
Parietal seizures symptomatogenic zone
May be distant from the seizure onset zone, with the seizure semiology representing ictal propagation beyond the parietal association cortex.
Parietal lobe propagation pathways
Parietal lobe -> sensorimotor cortex, premotor eye field, supplementary motor cortex, or temporolimbic region
Parietal lobe semiology
Focal motor clonic contralateral to the epileptogenic zone, tonic posturing of extremities, oral-gestural automatisms, complex automatisms, painful or thermal or sexual/groin paresthesias, head deviation, Todd
Parietal lobe EEG
The ictal EEG - may be poorly informative/falsely localizing; can show diffuse voltage suppression followed by sharp waves spreading either anteriorly or posteriorly to the frontal or parietal operculum
Interictal epileptiform discharges, if present, are typically seen in the temporal region.
Occipital lobe seizures semiology
Often characterized by elementary visual hallucinations consisting of flashing or steady spots or simple geometric forms. Other manifestations: repeated eye blinking, tonic eye and head deviation, either ipsilateral or contralateral to the ictal discharge.
Often associated with vegetative phenomena as vomiting.
Occipital lobe seizures EEG
Ictal EEG may be normal if the seizure focus is in the medial or basal occipital regions.
False localization can occur.
Ictal EEG may become more evident as a low-voltage fast activity progressively followed by a rhythmic epileptiform discharge. Ictal EEG in occipital seizures may vary with the pathway of propagation, spreading to the temporal or frontal region or bilaterally. At times, the initial ictal onset is missed while the ictal discharge rapidly becomes predominant in the temporal region giving a false lateralization.
The interictal EEG in occipital lobe epilepsy is typically abnormal. Posterior temporal epileptiform discharges are the most common patterns. Centrotemporal spikes are frequently seen with occipital paroxysms. Other patterns include random unilateral or bilateral occipital spikes, often with fixation-off sensitivity.
Fixation-off sensitivity is characterized by posterior or generalized epileptiform discharges that consistently occur after eye closure and last as long as the eyes are closed. It may represent an ictal or incterictal phenomenon. Some patients may also have occipital spikes exclusively during sleep, wile others may consistently have a normal EEG.
Insula connections
It has extensive connections with temporal, occipital, opercular, and orbitofrontla regions, and with the triangular and opercular parts of the inferior frontal gyrus
Insular seizures semiology
Seizures restricted to the insular do not result in impairment of consciousness and may manifest as laryngeal discomfort with thoracoabdominal constriction or dyspnea, vomiting, hyper salivation, laryngeal constriction, followed by unpleasant paresthesias or warmth in the perioral region or involving larger somatic areas, dysarthria, or dysphonia, ending with focal motor manifestations
Insular seizures EEG
The distance of the insular cortex from the surface makes scalp recording imprecise. Ictal EEG often is marked by muscle artifact and can show ictal discharges in the temporal regions. interictal discharges on scalp EEG are usually absent.
