WS1.4. Generalized Epilep tiform Patterns – Interictal and Ictal: Defining the Clinical Syndrome

Abstract

Generalised epileptiform patterns (GEPs) are bilateral and synchronous epileptiform discharges that appear over corresponding parts of both hemispheres, or the whole brain. Their morphology, amplitude and timing should be the same or similar over both hemispheres. The distinction between ictal and interictal GEPs is generally less clear compared with focal patterns. Ictal patterns often represent longer repetitions of interictal patterns. Clinical signs are more likely to be apparent during GEPs if the bursts are longer, the spike component is more persistent, and tests of responsiveness are adequately and repeatedly tested by the EEG technician. GEPs include 3Hz spike-wave discharges, polyspike-wave discharges, slow spike- wave discharges, generalised paroxysmal fast activity, electrodecremental response, photosensitive responses and ictal patterns. 3Hz spike and wave complexes are characteristic of idiopathic (genetic) generalised epilepsy, which includes childhood absence, juvenile absence and juvenile myoclonic epilepsy as well as epilepsy with generalised tonic-clonic seizures only. In children with 3Hz spike and wave, spontaneous remission is more likely if there is co-existent OIRDA and less likely if there is co-existent photoparoxysmal responses. Polyspike and wave complexes, either single or repetitive, can be seen in both idiopathic (typically in JME) and symptomatic generalised epilepsies. Slow spike and wave complexes occur at a frequency of 1.5–2.5 Hz and usually arise from an abnormal background; they, along with generalised paroxysmal fast activity (GPFA-bilaterally synchronous10–25 Hz activity) are typically seen in symptomatic and cryptogenic generalised epilepsies, notably Lennox-Gastaut syndrome. GPFA is typically seen in tonic seizures, but may also accompany atonic and generalised tonic-clonic seizures. Electrodecremental responses are seen in the atonic and tonic seizures of symptomatic and cryptogenic generalised epilepsies. Photoparoxysmal responses are bursts of generalised spike or polyspike and wave discharges that appear at certain flash frequencies and may outlast the stimulus.