EEG and semiology in focal epilepsy

Question 1

Generalized vs focal seizures

Answer 1

Generalized seizures appears to have a bilateral onset as the seizure rapidly involves bilateral networks. Focal seizures arise within networks limited to one hemisphere.

Question 2

In what percentage of people does scalp EEG fail to lateralize?

Answer 2

25% in patients with unilateral mesiotemporal epilepsy; 33-50% in patients with extratemporal epilepsy

Question 3

How can focal seizures be divided?

Answer 3

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

Question 4

Dystonic limb posturing

Answer 4

Contralateral

Question 5

Early head turn

Answer 5

Ipsilateral

Question 6

Late/versive head turn in transition to generalization

Answer 6

Contralateral

Question 7

Figure of 4 sign

Answer 7

Contralateral to the tonically extended arm

Question 8

Todd’s paralysis

Answer 8

Contralateral

Question 9

Focal clonic activity

Answer 9

Contralateral

Question 10

Unilateral eye blinking

Answer 10

Ipsilateral

Question 11

Unilateral limb motor automatisms

Answer 11

Ipsilateral

Question 12

Postictal nose wiping

Answer 12

Ipsilateral

Question 13

Preservation of ictal speech

Answer 13

Nondominant temporal lobe

Question 14

Postictal aphasia

Answer 14

Dominant hemisphere

Question 15

Ictal speech arrest

Answer 15

Dominant temporal lobe

Question 16

Ictal vomiting

Answer 16

Nondominant temporal lobe

Question 17

Hypermotor

Answer 17

Frontal lobe, less commonly insular or even temporal

Question 18

Ictal urinary urgency

Answer 18

Nondominant temporal lobe

Question 19

Limb parasthesia

Answer 19

Contralateral parietal lobe

Question 20

Simple visual hallucinations

Answer 20

Contralateral occipital lobe

Question 21

Complex visual hallucination

Answer 21

Contralateral temporo-occipital lobe

Question 22

Temporal lobe seizures

Answer 22

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

Question 23

Extratemporal seizures

Answer 23

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

Question 24

Frontal lobe seizures

Answer 24

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.

Question 25

SMA seizures

Answer 25

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

Question 26

Anterior cingulate seizures

Answer 26

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

Question 27

Orbitofrontal seizures

Answer 27

Sudden complex gestural automatisms, hyper motor activity, olfactory aura, fear and prominent facia expressions of fear, hallucinations, illusions, and prominent autonomic features

Question 28

Dorsolateral frontal seizures

Answer 28

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.

Question 29

Why can parietal and occipital lobe seizures present with temporal or frontal symptomatology?

Answer 29

Because of their spread from their locus of origin and are often the cause of pseudo temporal and pseudofrontal seizures.

Question 30

Parietal seizures symptomatogenic zone

Answer 30

May be distant from the seizure onset zone, with the seizure semiology representing ictal propagation beyond the parietal association cortex.

Question 31

Parietal lobe propagation pathways

Answer 31

Parietal lobe -> sensorimotor cortex, premotor eye field, supplementary motor cortex, or temporolimbic region

Question 32

Parietal lobe semiology

Answer 32

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

Question 33

Parietal lobe EEG

Answer 33

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.

Question 34

Occipital lobe seizures semiology

Answer 34

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.

Question 35

Occipital lobe seizures EEG

Answer 35

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.

Question 36

Insula connections

Answer 36

It has extensive connections with temporal, occipital, opercular, and orbitofrontla regions, and with the triangular and opercular parts of the inferior frontal gyrus

Question 37

Insular seizures semiology

Answer 37

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

Question 38

Insular seizures EEG

Answer 38

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.