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typical absence seizures. The discharge is often slightly faster than 3 Hz at onset, and tends
to slow down towards the end of the seizure. Inter-ictal EEG is normal, but may show runs
of occipital rhythmic delta (1540% of cases), which can persist in some children after
remission of absences. Photosensitivity is uncommon (less than 10%), and may be a marker
of poorer prognosis, as do myoclonic jerks of the eyes, mouth or limbs. Video recordings
now made routinely during standard EEGs help define these variations in CAE, and it is
increasingly recognised in paediatric practice that the more precisely the epilepsy syndrome
can be defined the more accurate the advice on prognosis and treatment becomes19. Patients
with juvenile absence epilepsy are more likely to show polyspike discharge or spike-wave
frequency above 3 Hz, and occipital rhythmic delta is not seen. In juvenile myoclonic
epilepsy, the inter-ictal and ictal EEG characteristic is brief bursts of polyspike (but
sometimes single spike) and wave discharge. Photosensitivity is relatively common in JME
(4050%), and seizures can be induced by other reflex mechanisms including reading or
praxis induction. Prominent polyspike wave discharge is also seen in eyelid myoclonia with
absence epilepsy. Generalised tonic-clonic seizures on awakening have no distinct EEG
features.

A retrospective evaluation of EEG features in IGE found only one-third showed typical
features on the first EEG17. While serial EEG records were necessary to elucidate syndromic
diagnosis, appropriate treatment could be initiated in a majority of cases on clinical grounds
at presentation. Absence epilepsy was the syndrome most likely to show diagnostic EEG
abnormalities at initial investigation.

IGE beginning in adult life is now an established entity18. Most cases have either generalised
tonic-clonic seizures with or without myoclonus, and electro-clinical manifestations are
similar to those in IGE presenting at earlier ages.

Photosensitive epilepsy. Photosensitivity occurs in about 5% of all epilepsies, usually IGE,
but also in progressive myoclonic epilepsies. Photosensitivity has age-related expression,
with three-quarters of cases having the first photic induced fit between the ages of 8–20
years20, and photosensitivity is twice as common in females. Longitudinal follow-up studies
have revealed persistence of photoparoxysmal responses and hence seizure risk in the
majority of cases of photosensitive epilepsy, without age limit. Photoparoxysmal EEG
abnormalities can occur as an acute symptomatic phenomenon on abrupt withdrawal of
alcohol or certain drugs, but are not then associated with long-term risk of epilepsy.

Benign childhood epilepsy syndrome. In benign childhood epilepsy with centro-temporal
spikes, the EEG hallmark is focal sharp wave discharges in central and temporal regions,
either bilateral or unilateral, and potentiated by sleep. Occasional patients show focal
discharges in other brain regions or generalised spike-wave activity. Background cerebral
rhythms are normal. Inter-ictal EEGs can show large amounts of ED, although frequent
epileptic seizures occur in only around one-quarter of cases, and the EEG trait may manifest
without clinical expression. Benign childhood occipital epilepsy (BCOE) has more variable
EEG features; paroxysms of occipital spike-wave on eye closure (fixation off sensitivity) are
characteristic of the early onset form or Panayiotopoulos syndrome. Otherwise, multifocal
discharges, rolandic spikes and generalised spike-wave are common, and the finding of
frequent multifocal discharges in a routine EEG should alert to BCOE in a child who has
occasional seizures or paroxysmal autonomic symptoms.

Landau-Kleffner syndrome (acquired aphasia and epilepsy) and electrical status epilepticus
in sleep. These disorders, which may be related, are characterised by continuous spike-wave
discharge occupying 85% or more of the sleep record. The wake EEG shows variable
findings.