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tongue. Vertiginous sensations are also thought to originate in the suprasylvian and possibly
the occipito-parietal region. Various seizure types may occur in a single patient at different
times.

The only primary motor seizures from the posterior brain regions are oculotonic and
oculoclonic seizures, or epileptic nystagmus, originating in the occipito-parietal cortex. The
nystagmus usually has the fast beating component to the site opposite the lesion or EEG
focus, i.e. contraversive. The nystagmus may occur as an isolated manifestation, or be
associated with head or trunk version, but rarely other motor activity accompanies, and
consciousness is usually retained. Eyelid flutter and rapid blinking are other features of
occipital epilepsy, often at the very beginning of seizures.

Provoking and associated/accompanying features1

Partial occipito-parietal seizures may be provoked by various stimuli involving the receptive,
interpretive and connective function of the parietal and occipital lobes. The most common
precipitating factor is photic stimulation, but other well-known inducers are tactile
stimulation, reading, drawing, calculation and other mental activity. The EEG may show
generalised changes, but focal electrical discharges in the posterior regions may occur. These
seizures are very rare.

Seizure spread from an occipital or parietal origin may cause a variety of motor activities;
some patients may have different patterns of seizure spread in different seizures, misleadingly
suggesting multifocal disease.

Post-ictal phenomena associated with parietal and occipital seizures are transient numbness,
inability to move despite no loss of power in affected limbs and post-ictal blindness. There is
no correlation between duration and severity of seizures and the duration of the post-ictal
neurological deficits. Post-ictal numbness and paralysis are usually short lasting, but post-
ictal blindness may be prolonged and, in some cases, permanent. Fixed hemianopia may help
confirm occipital lobe onset.

Causes

In a large series of patients with parietal lobe epilepsy from the Montreal Neurological
Institute5,6, tumours, gliosis and scarring were the commonest causes. Malformations,
vascular lesions and infarction were also described. In occipital lobe epilepsy, three-quarters
of patients may have underlying abnormalities shown on MRI. Causes include tumours,
trauma, malformations (focal cortical dysplasia, periventricular heterotopia, band heterotopia
and polymicrogyria), ischaemia, mitochondrial disease (with migraine, photosensitivity and
other neurological manifestations), Sturge-Weber syndrome and coeliac disease with bilateral
occipital calcifications. Occipital seizures can occur in hyperglycaemia and pre-eclampsia,
and may occur early in the course of Kuf’s disease or Lafora body disease. Three
subsyndromes of occipital epilepsy have been described in childhood and adolescence7-10.
Seizure semiology, the occurrence of amaurosis or migraines, and reactive EEG patterns do
not differentiate between idiopathic, often benign, and symptomatic occipital epilepsy. MRI
will identify most symptomatic cases. The relationship between migraine and occipital
epilepsy is complex7. The differential diagnosis may be difficult. Further, epileptic seizures
may evolve from an attack of migraine, and vice versa.