Identification of the epileptogenic zone in patients with tuberous sclerosis: concordance of interictal and ictal epileptiform activity.

OBJECTIVE

In the majority of patients with tuberous sclerosis complex (TSC) multifocal epileptiform activity is present interictally. Therefore, its value in identifying epilepsy surgery candidates has been doubted. We hypothesize that dominant interictal epileptiform foci are concordant with the ictal onset zone in TSC patients.

METHODS

Consistency and dominance of focal interictal epileptiform activity was assessed in 19 patients with a clinical definite diagnosis of TSC. The ictal onset zone was identified. Concordance between interictal en ictal findings was analyzed. If concordance was found epilepsy surgery was proposed.

RESULTS

We found dominant, consistently present, focal interictal epileptiform activity in 14 of the 19 patients. Concordance between the dominant interictal focus and the ictal onset zone was found in 11 of the 14 patients (79%). In one patient the ictal onset zone could not be identified and discordance was present in two patients. Epilepsy surgery was performed in six patients rendering three of them seizure free, and one had a seizure reduction >90%. In these patients local concordance was found whereas regional concordance was found in the two patients who did not benefit from epilepsy surgery.

CONCLUSIONS

A dominant as well as a consistent interictal focus is concordant with the ictal onset zone in the majority of TSC patients.

SIGNIFICANCE

Future studies of TSC patients addressing the value of interictal foci in the consideration of epilepsy surgery, in absence of clear ictal onset zone, are necessary.