Usefulness of low amplitude spikes with continuous focal periodic discharges on interictal scalp electroencephalogram and their patterns of cortical electroencephalogram

Abstract

Objective To reveal the influential factors on scalp electroencephalogram(EEG) recording and provide valuable information for localization of the epileptic focus by analyzing the characteristics of spikes with continuous focal periodic discharges on scalp and cortical EEG. Methods Five patients with refractory epilepsy who had low amplitude spikes with continuous focal periodic discharges on interictal scalp EEG were studied. Intracranial EEG recording was also performed in patients. The amplitudes of spikes and cortical areas of spike-wave foci were measured by DaVinci system. Patterns of continuous periodic activity were determined by autocorrelograms, power spectral density and coherence analysis using Matlab and Spike2 software. T-test was employed to compare the mean amplitudes of spikes on the scalp and cortical EEG. Results The amplitudes of spikes recorded on scalp EEG of the 5 patients were: (22.2±4.8), (30.4±7.1), (20.7±3.2), (58.4±10.1), (23.4±3.9) μV. The amplitudes of spikes recorded on cortical EEG of the 5 patients were: (1253.8±199.3), (806.5±161.4), (1585.7±305.7), (922.5±140.6), (736.8±70.9) μV. The amplitudes of spikes on scalp EEG were significantly higher than those on cortical EEG (t=6.394, P<0.05).The cortical areas of spike-wave foci of the 5 patients were: 4.0, 6.0, 3.5, 5.5, 6.5 cm2. Power spectral density and autocorrelograms showed 1—3 Hz oscillations on the cortical of spike-wave foci. Cross-correlation and coherence analysis showed synchronization of electrical activity in two contacts of intracranial electrodes. Conclusion The low amplitude spikes with continuous focal periodic discharges on interictal scalp EEG provide valuable information for localization of the epileptic focus. Key words: Scalp; Electroencephalography; Epilepsy; Cerebral cortex; Malformations of cortical development