Abstracts

Rationale: Epilepsy surgery can alter the course of epilepsy by improving or eliminating seizures in carefully selected patients with a focal cortical abnormality concordant to the EEG abnormality. However, a subset of children with intractable epilepsy has been deemed non-surgical candidates due to scalp EEG findings of generalized or discordant abnormalities. Wyllie et al. (2007) reported epilepsy surgery may be successful for these children with a congenital or early-acquired brain lesion, despite abundant generalized or bilateral EEG discharges. MEG is a non-invasive tool that can help in identifying patients in this group who may benefit from epilepsy surgery. Methods: We included three patients (2 boys, 1 girl) with refractory epilepsy, hemiplegia/hemiparesis and presurgical scalp EEG discharges (ictal and interictal) showing predominant (>50%) generalized or contralateral to the atrophic/lesional hemisphere noted on MRI. All 3 patients underwent scalp video EEG (VEEG), MRI and MEG as part of their presurgical evaluation. MEG was obtained with simultaneous EEG recording. Results: MRI showed hemispheric atrophy in all 3 patients. Scalp VEEG captured multiple seizures associated with non-localizing generalized discharges. All patients presented with epileptic spasms and/or tonic seizures. Only patient 2 showed lateralization by clinical semiology. In all patients, MEG revealed low amplitude spikes and clustered randomly oriented spike sources on the atrophic hemisphere. These MEG spikes at times preceded EEG spikes or appeared without corresponding EEG discharges. The contralateral hemisphere showed clustered spike sources around Rolandic region with identical orientations. Two patients underwent functional hemispherectomy and the pathology included Rasmussen’s encephalitis (patient 1) and mild malformation of cortical development (patient 3). They had significant improvement in seizure control (no more tonic or drop seizures, only staring episodes). Patient 2 is awaiting surgery and the serial MRI studies show progressive right hemiatrophy suggestive of Rasmussen’s encephalitis. Conclusions: MEG can reveal hidden epileptogenic spike sources in the atrophic hemisphere despite generalized or contralateral scalp EEG discharges. The uniform MEG Rolandic spike sources over the relatively normal hemisphere suggest that these spikes probably represent mirror and non-epileptogenic discharges due to an interaction between the epileptogenic lesion and the developing brain. MEG is a useful tool in helping identify selected children with hemiparesis and refractory seizures secondary to hemispheric disease despite generalized or non-lateralizing/contralateral scalp EEG abnormalities for epilepsy surgery.