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uncertain. Some children may have only one or two seizures, but others may not remit. Inter-
ictal EEG shows spontaneous and photically induced occipital spikes. Centrotemporal spikes
may coexist. Ictal EEG documented the occipital origin and the spreading of the discharges to
the temporal regions131,135. There remain no other significant precipitating factors in ICOE-G if
photosensitive patients are excluded. Despite FOS in EEG, only a few patients report seizure
precipitation by going from bright light to darkness or by darkness itself137.

Aetiology
There is an increased family history of epilepsies (21–37%) or migraine (9–16%)122,126,138 but
familial ICOE-G appears to be rare139,140.

Pathophysiology
The seizures are purely of occipital lobe origin. The epileptogenic zone involves wide and
bilateral networks within the occipital lobes and this localisation is congruent with the
symptomatogenic zone. Elementary visual hallucinations originate from the visual cortex,
complex visual hallucinations from the junction of the occipital with the parietal and temporal
lobes, formed visual illusions from the lateral occipital-posterior temporal junction and tonic
deviation of the eyes from the medial occipital cortex, above or below the calcarine sulcus. Ictal
blindness may reflect bi-occipital seizure spreading but this may not explain its sudden onset,
without any other preceding manifestations. From the EEG standpoint, the occipital paroxysms
are usually bilateral and synchronous because they are activated in both occipital regions by the
elimination of fixation (FOS) and central vision72 and not by thalamocortical activation
proposed by Gastaut and Zifkin122.

The mechanisms for post-ictal headache are unknown. It is likely that the occipital seizure
discharge triggers a genuine migraine headache through trigeminovascular or brain-stem
mechanisms124,141.

Diagnostic procedures
By definition, all tests other than the EEG are normal. However, high-resolution MRI is
mandatory, because symptomatic occipital epilepsy present with the same clinical-EEG
manifestations.

Electroencephalography
The inter-ictal EEG shows occipital paroxysms121,122, often demonstrating FOS72,142. Because
terminology is often unclear and FOS is not always tested, the prevalence of classical occipital
paroxysms with FOS is uncertain and ranges between 100%122, 88%126 and 19%2. Some patients
may have only random occipital spikes, whereas others may have occipital spikes only in sleep
EEG and some may have a consistently normal EEG124. Centrotemporal, frontal and GSES
occur together with occipital spikes in around 20% of patients122,143. IPS consistently elicits
occipital spikes and/or generalised discharges in photosensitive patients.

As happens with the rolandic spikes, occipital spikes are not pathognomonic of any particular
syndrome, because they also occur in a variety of organic brain diseases with or without
seizures, in children with congenital or early onset visual and ocular deficits, and even in 0.5–
1.2 % of normal pre-school age children39,40,144. They are common in young children with a
peak age at first discovery of 4–5 years, and ‘tend to disappear in adult life, and the subsidence
of the EEG abnormality is usually accompanied by a cessation of seizures’40,144.

There are many reported ictal EEGs92,121,122,133,145-148. Seizure onset is preceded by regression of
occipital paroxysms, and is characterised by the sudden appearance of an occipital discharge
that consists of fast rhythms, fast spikes or both and is of much lower amplitude than the
occipital paroxysms. Elementary visual hallucinations relate to the initially fast spike activity
and complex visual hallucinations may occur when the ictal discharge is slower. In oculoclonic