Sentinel Epileptiform Discharges Activating Two Seizure Networks on Intracranial EEG.

SUMMARY Sentinel epileptiform discharges (SEDs) are epileptiform transients preceding the onset of a focal seizure seen on scalp EEG. Despite their potential localizing value, formal study of SED has been limited. The authors report a patient with MRI-negative focal-onset epilepsy whose seizures on scalp and intracranial EEG were always preceded by SED. Although the location and morphology of the SED was invariable, the seizures after the discharge were of two clearly distinct types, each with different semiology and region of spread on intracranial EEG. This suggests that the SED played a role in activating two distinct seizure networks. A right temporal lobectomy with amygdalohippocampectomy was performed. The resection included both the region of the SED as well as the seizure-onset zone of the more common seizure type, achieving seizure freedom at 3 years after surgery. Further research exploring whether the localization of SED is a reliable indicator of the seizure-onset zone could aid surgical planning in patients whose seizures are preceded by SED.