Invasive EEG in Neocortical Epilepsy Seizure Onset
Source: in Neocortical Epilepsies. Williamson, P.D.; Siegel, A.M.; Roberts, D.W.; Thadani, V.M.; Gazzaniga, M.S.; eds. Philadelphia, PA, Lippincott Williams and Wilkins, pp. 275-285, September 2000.
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Summary: Invasive EEG in Neocortical Epilepsy: Seizure Onset, a chapter in Neocortical Epilepsies, describes a study that examined 53 people with refractory neocortical epilepsy at the Yale Epilepsy Center. The patients were studied with implanted intracranial electrodes, had their seizure onset recorded and stored for review, and had subsequent resective surgery with pathological analysis and at least 1 year of followup. Researchers used outcome and pathology to judge the success or failure of localization by the detected signals, analyzing characteristics of seizure onset in the neocortex. Data analysis indicated that slow onset alone did not predict poor outcome, nor did regional seizure onset. There was no significant relationship between distribution or frequency of onset and outcome or pathology. However, frequency and distribution of seizure onset in neocortex recorded with implanted electrodes were characteristic of the anatomic region itself. Researchers found two particular morphologies of seizure onset (low voltage fast activity and rhythmic sinusoidal waves) that predicted good surgical outcome, although they were not associated with specific substrates. A preictal periodic spike discharge, previously characterized as typical of mesial temporal sclerosis, was seen in 14 people with neocortical seizures. The researchers hypothesize that the frequency, lobe, and distribution of seizure onset recorded by implanted electrodes in medically uncontrolled neocortical epilepsy significantly correlate with each other but not with outcome or pathology, which suggests that such features are determined by the anatomic location and its networks or connections, independent of the epilepsy etiology, cellular alterations, or mechanism of epilepto genesis. However, the morphology or waveform of seizure onset, the underlying pathology, and surgical outcome significantly relate with each other. This suggests that waveform is a characteristic of specific pathophysiology and may be used in predicting the underlying substrate.
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