Abstracts

Rationale: It is not uncommon for scalp ictal EEG changes to be nonlateralizing in the setting of focal epilepsy diagnosed unambiguously on alternative grounds. We describe three patients with nonlateralizing scalp ictal EEG, in whom the pattern of EMG artifact correctly implicated the hemisphere of seizure onset as contralateral to the side of greater artifact. Methods: Retrospective review of video-EEG (VEEG) monitoring data on three patients. Results: 1) A 30 year old woman with left neocortical temporal lobe epilepsy experienced two generalized seizures with nonlateralizing semiology and diffuse ictal EEG. The early phase of the latter showed more abundant right sided EMG artifact. Brain MRI showed left temporal pole encephalomalacia; interictal spikes were maximum over the left midtemporal region. 2) A 42 year old man with left frontal lobe epilepsy had two generalized seizures preceded by versive rightward head deviation. Ictal EEG was nonlateralizing, though EMG artifact in the early phase was higher over the right. Brain MRI showed bilateral orbitofrontal encephalomalacia with extensive gliotic change on the left; interictal epileptiform was bilateral though higher on the left. 3) A 45-year old woman with left neocortical temporal lobe epilepsy had three secondarily generalized seizures with poor ictal EEG localization. EMG artifact was higher over the right in the initial phase of the motor seizure. Brain MRI was nonlesional; interictal epileptiform activity was restricted to the left temporal region. All three patients proceeded to invasive monitoring with subdural grid electrodes. Intracranial EEG confirmed the ictal onset zone over the left neocortical temporal, left orbitofrontal, and left anterior temporal regions respectively. Conclusions: EMG artifact on scalp EEG, normally ignored as a contaminant, is prominent in convulsive seizures. Its asymmetry in the early phase of motor seizures, implying subtle asymmetry of tonic posturing, may provide valuable lateralizing information when the ictal EEG is itself uninformative. When seizure semiology is also nonlateralizing, asymmetric EMG may be the only VEEG observable that points to the hemisphere of ictal onset. A larger study is under way to confirm these pilot observations.