Purpose: Traditionally, seizure onset localization in ictal electro-encephalography (EEG) is the main factor guiding resective epilepsy surgery. The situation is often different in infantile epileptic encephalopathy. We demonstrate the importance of the underrated interictal (rather than ictal) surface EEG in informing decision-making in epilepsy surgery for children with epileptic encephalopathy caused by subtle focal cortical dysplasia (FCD).
Methods: We present a small case series of three children who had an epileptic encephalopathy with either epileptic spasms or tonic seizures. All three were thought initially to have normal neuroimaging.
Results: Ictal EEG localizing features were seen in none and lateralizing features were seen only clinically in one of the three. However, the interictal EEG showed persistent and consistent focal irregular slowing in all, particularly after medically resolving the diffuse encephalopathy. Subtle FCDs were uncovered in all. Surgery was performed in all with excellent outcome.
Conclusion: In infantile epileptic encephalopathy caused by subtle FCD, the often underrated interictal surface EEG (particularly persistent foal irregular slowing) informs the most; not only to the target area for surgical resection but also to its extent. This may negate the need for unnecessary and sometimes non-informative invasive monitoring in these cases. A matter of "zooming out" to define the extent of a resectable abnormality rather than "zooming in" to define a seemingly localized epileptic focus that may change with time.
Keywords: Epilepsy surgery; Epileptic encephalopathy; Focal slowing; Interictal EEG.