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seizures, spikes and spike-wave complexes are slower, and a localised ictal fast spike rhythm
may occur before deviation of the eyes. Ictal EEG during blindness is characterised by pseudo-
periodic slow waves and spikes, which differ from those seen in ictal visual hallucinations.
There are usually no post-ictal abnormalities.

Differential diagnosis
The differential diagnosis of ICOE-G is mainly from symptomatic occipital epilepsy, migraine
with aura, acephalgic and basilar migraine where misdiagnosis is very high2,124.

Patients with symptomatic occipital epilepsy may often have symptoms identical to those of
ICOE-G with normal neuro-ophthalmological examination and routine brain imaging. Thus,
high-resolution MRI is required to detect subtle lesions149. Occipital seizures of mitochondrial
disorders, Lafora disease and coeliac disease should be considered2,84.

The differential diagnosis of ICOE-G from migraine is usually easy if all clinical elements are
properly assessed and synthesised. Contrary to visual seizures, visual aura of migraine develops
slowly within minutes, lasts for 10–20 minutes and consists of mainly achromatic and linear
patterns150-152. Illustration of the visual symptoms of the attacks by the patient is a powerful tool
in differential diagnosis and to inform objective analysis. Orbital pain in the ictal phase of visual
hallucinations is typical of occipital seizures and does not occur in migraine. However, post-
attack headache is common and similar for both occipital epilepsy and migraine. Basilar
migraine attacks also develop slowly within minutes, last for 30–60 minutes and consist of
mainly bilateral impairment of vision associated with, or followed by, neurological symptoms
such as vertigo, tinnitus, ataxia, bilateral weakness and dysaesthesiae which do not occur in
occipital lobe epilepsy141. Mistaking visual seizures for migraine attacks may be common in
publications referring to controversial diagnostic terms such as ‘migralepsy’ and ‘basilar
migraine with occipital paroxysms’. A critical review of such reported cases indicates that these
are likely to be genuine occipital seizures imitating migraine141.

ICOE-G is distinctive from PS (Table 1) and the differences have been statistically validated2
despite some overlapping features. A key point in the differential diagnosis is that seizure onset
is primarily with visual symptoms in ICOE-G and with autonomic manifestations in PS.

Prognosis
The prognosis of ICOE-G is unclear, although available data indicate that remission occurs in
50–60% of patients within 2–4 years of onset122,124,126. Seizures show a dramatically good
response to carbamazepine in more than 90% of patients. However, 40–50% of patients may
continue having visual seizures and infrequent secondarily GTCS. Rarely, atypical evolutions
to epilepsy with CSWS and cognitive deterioration have been reported153. Also rarely, children
with ICOE-G may manifest with typical absence seizures, which usually appear after the onset
of occipital seizures154.

The performance scores for attention, memory and intellectual functioning were lower in
patients with ICOE-G than control subjects though basic neurophysiological functions did not
differ significantly155.

Other phenotypes of BCSSS

There are reports of children suffering from benign childhood focal seizures with clinical-EEG
manifestations that cannot be classified as rolandic epilepsy, PS or ICOE-G. They may
represent rare, atypical or overlapping presentations of BCSSS.