Asymmetric Scalp Electromyogram

Abstract

The early phase of motor seizures in focal epilepsy produces asymmetry of scalp electromyogram (ASEMG), observable as right-left inequality in muscle artifact on EEG. ASEMG is concordant with clinical lateralization when the seizure has clearly unilateral motor features (tonic, clonic, or versive movements), with higher electromyogram contralateral to the hemisphere of seizure onset. The authors explored whether ASEMG was also present in motor seizures without visible lateralizing signs. Seizure classification by video telemetry data in a group of 106 focal epilepsy patients by semiology and ictal EEG. Assessment of ASEMG laterality by two reviewers. Computation of the κ index of interobserver reliability. Calculation of the sensitivity and positive predictive value of ASEMG in motor seizures with regard to the laterality of the epileptogenic zone. Forty-eight of 106 patients had at least 1 motor seizure recorded. Of the total of 257 seizures recorded in the former, 174 (≈68%) had a motor component. Forty such seizures had no clinical or EEG lateralization; ASEMG was, however, identified and accurate in 39 (97.5%). Generally, ASEMG was identified in 158 (90.8%) of all motor seizures, correctly lateralizing 156 (89.6%). The next most common lateralizing sign was unilateral tonic, clonic, or dystonic posturing (44.8%). ASEMG is an accurate lateralizing sign, useful in seizures that have no alternative clinical lateralizing signs or ictal EEG lateralization. ASEMG was present in >90% of all motor seizures in this series, with a positive predictive value of 156 (>98%) of 158.