Focal Ictal EEG Lecture Notes

Vocabulary terms and clinical definitions regarding focal ictal EEG patterns, classification changes, and localization limitations based on the University of Sydney lecture by Andrew Bleasel.

Spikes

Paroxysmal epileptiform activity distinct from background rhythms with a duration of less than $70\,msec$.

Sharps

Paroxysmal epileptiform activity distinct from background rhythms with a duration between $70\text{--}200\,msec$.

Ictal EEG

A superior study to interictal EEG in the diagnosis of epilepsy, often recorded with video (VEEG) while medications are reduced.

EEG Seizure Features

Common characteristics including abrupt disruption of background rhythms, rhythmic slowing or repetitive discharges, and evolution of morphology, frequency, and distribution.

Evolution (Ictal)

The progressive change in the morphology, frequency, and distribution of an EEG pattern during a seizure event.

Temporal Lobe Seizure Pattern

Often consists of $5\text{--}7\,Hz$ rhythmic sharp theta activity ($50\text{--}80\%$), maximal at anterior and inferior temporal electrodes.

Delayed focal onset

A term from Rissenger et al. 1989 describing ictal EEG changes that appear well after the clinical onset of a seizure.

Frontal Lobe Seizures

Seizures where approximately $30\%$ show localising features; they more often show bilateral changes or are obscured by movement artefact.

Parietal Lobe Seizures

A type of extratemporal seizure where less than $10\%$ show localising features on scalp EEG.

Occipital Lobe Seizures

Seizures showing $50\%$ lateralisation in the posterior hemisphere but less than $20\%$ localisation (Rissenger, 2000).

Mu

A normal rhythm of wakefulness that serves as an ictal EEG pitfall because it can appear to be "spikes."

Focal Aware

The New ILAE Classification for simple partial seizures where consciousness is preserved during the seizure.

Focal Impaired Awareness

The New ILAE Classification for complex partial seizures where consciousness is lost during the seizure.

Focal to bilateral tonic-clonic

The New ILAE Classification for partial seizures that progress to become secondarily generalised seizures.

Simple Partial Seizure (SPS) Ictal Correlate

An ictal EEG correlate is found in $20\%$ of cases (Devinsky et al., 1988) or $35\%$ with expanded surface electrode arrays (Bare et al., 1994).

Temporal EEG Localization (MRI Lesions)

Exclusively temporal discharges found in $59\%$ of cases with temporal lesions according to Remi et al. (2011).

Frontal EEG Localization (MRI Lesions)

Exclusively frontal discharges found in $27\%$ of cases with frontal lesions according to Remi et al. (2011).

Scalp EEG Limitations

Includes limited brain coverage, potential lack of changes with frontal or mesial foci, rapid seizure spread, and common movement artefacts.