Page 121 - ILAE_Lectures_2015

The Commission on Classification of the ILAE3 defined IGE as follows:

Idiopathic generalised epilepsies are forms of generalised epilepsies in which all
seizures are initially generalised (absences, myoclonic jerks and generalised tonic-
clonic seizures), with an EEG expression that is a generalised bilateral,
synchronous, symmetrical discharge (such as is described in the seizure
classification of the corresponding type). The patient usually has a normal inter-
ictal state, without neurological or neuroradiologic signs. In general, inter-ictal
EEGs show normal background activity and generalised discharges, such as spikes,
polyspike spike-wave, and polyspike-waves 3 Hz. The discharges are increased by
slow sleep. The various syndromes of idiopathic generalised epilepsies differ mainly
in age of onset. No aetiology can be found other than a genetic predisposition
towards these disorders.

The seizures in IGE

The seizures of IGE are TA, myoclonic jerks and GTCS2,3. Of these, TA occupy a central
position as they occur almost exclusively in the context of the IGEs2, and are
neurophysiologically and pharmacologically unique13,14, which in turn makes their treatment
different.

1. Typical absences
TA are brief, generalised epileptic seizures, characterised clinically by impairment of
consciousness (absence) that occurs without warning and also ceases suddenly and without
post-ictal symptoms, and electrographically by generalised 4–3 Hz spike and slow-wave
discharge2 that terminates without subsequent electrical flattening. Along these rather strict
lines, TA tend to display a considerable clinical and EEG variability that may be syndrome-
related.

Impairment of consciousness may range from mild to severe, and may occur either in
isolation, or in association with other ictal manifestations, such as automatisms, autonomic
signs, and regional (mouth or eyes) or widespread (head, limbs, and trunk) rhythmic or
random myoclonia. Clinical subtypes of TA therefore include absences with impairment of
consciousness only, with clonic, atonic, tonic, or autonomic components, and with
automatisms2,15,16. In turn, the accompanying EEG discharge may be very brief or long
(usually between 3 and 30 seconds), continuous or fragmented, with regular or varying
intradischarge frequency, may display spike or multiple spike components, and even show
non-consistent side preponderance. It is usually faster and unstable in the opening phase
(first second), becomes more regular and stable in the initial phase (next three seconds), and
slows down towards the terminal phase (last three seconds). Background activity is normal,
and inter-ictal fast, non-localising spikes may occur, usually over the frontal areas.

TA may occur spontaneously, and are typically provoked by hyperventilation, but also by
other specific triggers, e.g. photic or pattern stimulation, video games, thinking, or even
reading. They may be the sole or the predominant seizure type in individual patients, such
as in CAE or juvenile absence epilepsy (JAE), or coexist with other generalised seizures,
such as GTCS or myoclonic jerks, as in JME. Natural history may also vary: TA may remit
with age or persist requiring continuous treatment; approximately 10–15% of adults with
epilepsies have TA, often combined with other types of generalised seizures17-19.

A distinction should be made between typical and atypical absences. As opposed to TA,
atypical absences2 occur only in the context of mainly severe symptomatic or cryptogenic
epilepsies of children with learning difficulties, who also suffer from frequent seizures of
other types such as atonic, tonic, and myoclonic seizures. Clinically, onset and offset may