Page 123 - ILAE_Lectures_2015

The syndromes of IGE

Epilepsy syndromes, defined as clusters of symptoms or signs occurring consistently
together, form the basis of the currently accepted classification of the epilepsies, and such
a concept is practical for diagnosis, orientation of treatment and prognosis, and selection of
appropriate investigations. A number of IGE syndromes feature in the current3 and the
recently proposed7 classification systems of the ILAE, while others have not been
recognised yet. In addition, there are patients with IGE who do not fit easily into
recognisable syndromes.

The IGE syndromes currently recognised by the ILAE are shown in Table 1. Benign
neonatal familial convulsions, benign neonatal convulsions and benign myoclonic epilepsy
in infancy are not dealt with here.

IGE syndromes not yet recognised by the Commission of the ILAE include eyelid myoclonia
with absences (EMA), perioral myoclonia with absences (PMA), idiopathic generalised
epilepsy with phantom absences, and stimulus-sensitive absence epilepsies.

Childhood absence epilepsy (CAE)12,20,22 is the archetypal syndrome of typical absence
seizures, with onset usually before the age of ten years and a peak at 5–6 years. The
prevalence of CAE is 10–12% for children with epilepsy younger than 16 years of age23,24.
As a rule, TA is the only seizure type at presentation and for the first active period of
absences, but infrequent GTCS may occur in adolescence or adult life. TA occur frequently
(tens or hundreds per day), last for 4–30 seconds (usually around 10 seconds), and are
associated with severe impairment of consciousness.

Clinically, there is abrupt and severe loss of awareness, and complete unresponsiveness.
The eyes spontaneously open and stare or move slowly, and all voluntary activity stops
within the first 3 seconds of the seizure. Random eyelid blinking (usually not sustained)
may occur, and mild, mainly orofacial, automatisms are frequent15. There may also be a
transient impairment of postural tone, resulting in the head, limbs or trunk dropping, and
sometimes an increase in tone that leads to retropulsion. Ictal clinical symptoms and signs
inconsistent with CAE include mild impairment of consciousness, pronounced and
rhythmical myoclonus either regional (eyelid or perioral) or massive limb jerking, and
single or arrhythmic myoclonic jerks of the head, trunk, or limbs. The occurrence of other
generalised seizures, such as GTCS, or myoclonic jerks, prior to or during the active period
of the absences, and sensitivity to photic or other sensory triggers is also thought to be
incompatible with CAE12,20,22. The background EEG is normal with frequent rhythmic
posterior delta activity. Ictal discharges consist of generalised high amplitude 2.5–4 Hz
spike-wave and are longer than 4 seconds.

Prognosis and evolution of CAE depends on the applied diagnostic criteria. Delineated as
above, CAE has an excellent prognosis; TA are responsive to treatment and remission
occurs in more than 80–90% of children before the age of 12 years. However prognosis
becomes variable when one includes in CAE every child with onset of absences before the
age of ten years. GTCS occur in perhaps more than one-third of patients, either during
adolescence25 or in the third decade of life26, and some patients may develop JME1,27. TA
in these patients may persist, improve or disappear. Most of the available evidence on the
prognosis of CAE is inconclusive, and certainly one could argue that such patients may not
have CAE but another form of IGE (JAE or JME).