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Electroencephalographic features

In somatosensory epilepsy, the localisation of electrical discharges on scalp EEG often cannot
be correlated with a clinical ictal pattern and the seizures are often electrically silent. EEG
changes may be lateralising rather than localising. Sometimes slow activity is most
prominent. The two most common EEG features observed are central parietal spike or spike-
wave discharges that may be sustained during the ictus, and temporal discharges, with
occasionally more posterior spread. During seizures, spread often involves the motor cortex,
and the supplementary motor or speech areas of the frontal lobes. Spread to the temporal
lobes is said to be rare, but has been described and reproduced by electrical stimulation.
Secondary bilateral synchrony may occur.

Changes in the posterior background activity may be helpful in occipital lobe epilepsy.
Occipital foci are often widespread and may move between the occipital pole and the anterior
temporal lobes. Spread seems to be to the parietal and frontal regions when the discharge
originates in the supracalcarine region, but to the ipsilateral temporal lobe when the epileptic
activity arises in the infracalcarine cortex. Spread to the contralateral occipital lobe via the
corpus callosum seems to occur late in adult cases. Electrical abnormalities may be confined
to the temporal lobes, and depth electrode studies in patients with complex partial seizures
have in some cases revealed an occipital origin of the epilepsy, although such origin has not
been reflected in the clinical picture of the seizures or revealed by scalp EEG. Occipital onset
seizures may therefore be more prevalent than previously thought.

Treatment

The medical treatment of occipital and parietal epilepsy is no different to that of other focal
epilepsies. Surgical series are less comprehensive than those in temporal lobe epilepsy.
Historical series suggest 20% of non-tumoural and 75% of tumoural parietal lobe cases may
be rendered seizure-free by resective surgery5,6. These figures will probably improve with the
application of modern neuroimaging methods and better case selection. Surgical outcome in
refractory occipital lobe epilepsy depends largely on the underlying pathology. Outcome is
better for tumours than for developmental abnormalities11.

Surgery to the parietal and occipital lobes carries the likelihood of resulting in a fixed deficit,
particularly a visual field defect, somatosensory or higher cognitive impairment. This must
explained carefully to the patient in the discussion of the risk-benefit ratio9,12,13.

References

1. SVEINBJÖRNSDÒTTIR S, DUNCAN JS. Parietal and occipital epilepsy. Epilepsia 1993; 34: 493-521.
2. SALANOVA V. Parietal lobe epilepsy. J Clin Neurophysiol 2012; 29(5): 392-6.
3. ADCOCK JE, PANAYIOTOPOULOS CP. Occipital lobe seizures and epilepsies. J Clin Neurophysiol 2012;

29(5): 397-407.
4. NGUYEN DK, NGUYEN DB, MALAK R, BOUTHILLIER A. Insular cortex epilepsy: an overview. Can J

Neurol Sci 2009; 36 Suppl 2: S58-62.
5. SALANOVA V, ANDERMANN F, RASMUSSEN T et al. Clinical manifestations and outcome in 82 patients

treated surgically between 1929 and 1988. Brain 1995; 118: 607-627.
6. SALANOVA V, ANDERMANN F, RASMUSSEN T et al. Tumoural parietal lobe epilepsy. Brain 1995; 118:

1289-1304.
7. CARABALLO, R., KOUTROUMANIDIS, M., PANAYIOTOPOULOS, C.P., FEJERMAN, N. Idiopathic

childhood occipital epilepsy of Gastaut: a review and differentiation from migraine and other epilepsies. J Child
Neurol 2009; 24: 1536-42.
8. MICHAEL M, TSATSOU K, FERRIE CD. Panayiotopoulos syndrome: an important childhood autonomic
epilepsy to be differentiated from occipital epilepsy and acute non-epileptic disorders. Brain Dev 2010; 32: 4-9.
9. PANAYIOTOPOULOS CP, MICHAEL M, SANDERS S, VALETA T, KOUTROUMANIDIS M. Benign
childhood focal epilepsies: assessment of established and newly recognised syndromes. Brain 2008; 131: 2264-
86.
10. KOUTROUMANIDIS M. Panayiotopoulos syndrome: and important electroclinical example of benign childhood
system epilepsy. Epilepsia 2007; 48: 1044-53.