Scott, Catherine Anne; (2002) Current role of ictal scalp EEG in evaluation for epilepsy surgery. Doctoral thesis (M.Phil.), UCL (University College London).

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Abstract

Scalp EEG-video telemetry, a time consuming and expensive investigation, is routine in all patients prior to surgery in the majority of epilepsy centres. With the introduction of MRI, which can usually identify the underlying pathological substrate associated with the patient's epilepsy, its role has become less clear. The aim of this study was to clarify the current role of pre-surgical scalp EEG- video telemetry, by investigating whether specific ictal features were (i) associated with different pathologies, (ii) the likelihood of proceeding to surgery, or (iii) the post-operative outcome. This study also determined how often in this setting additional information was recorded that might modify the decision making process. Four hundred consecutive patients undergoing scalp telemetry were studied, and the recordings analysed blind to the imaging data with regard to specific ictal EEG features. Seizure semiology was analysed separately. The outcome was determined at least one year post-operatively (range 1–6.5 years). The presence of lateralised ictal temporal theta was significantly associated with a temporal location of pathology, and temporal lobe type seizure semiology. A combination of early and sustained lateralised theta was significantly associated with unilateral hippocampal sclerosis (UHS) (n=190) in comparison to the other imaging groups (n=210). The combination of temporal lobe seizure type and UHS was the best predictor of proceeding to surgery (increasing the likelihood sixfold), but individual analysis of specific ictal EEG features did not predict post-operative outcome within specific imaging subgroups. Overall video-EEG telemetry provided evidence of non-epileptic attacks in 3%, and grossly discordant electroclinical data compared to the neuroimaging findings in 10% of patients studied. Therefore, ictal scalp EEG recordings have a relatively low yield of information that influences decisions concerning epilepsy surgery over and above the evaluation of seizure semiology and underlying pathology.

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