Abstracts

Rationale: Cortical dysplasia (CD) has an acknowledged association with epilepsy treatment. The aim of this study was to identify ictal and inter-ictal patterns in electroencephalographs (EEG) of focal and extensive CDs (FCD and ECD). This is part of a wider ongoing study, looking at markers of intractability in CD in childhood, by reviewing clinical, neurophysiological and imaging data. Method: A retrospective review of 17 children referred to the epilepsy surgery programme, with a confirmed diagnosis of CD (9 males, 8 females, age range 0.25-18.42yrs, mean age 5.9yrs). All the patients had undergone ictal scalp EEG with video telemetry and SPECT. In 9 of the cases, subdural recordings were also reviewed.The EEGs were examined to look at morphology of activity, at onset of and during seizure . In the cases were both scalp and subdural recordings were made, a comparison of the findings was performed. Findings in FCDs (where the abnormality had a well-defined border, usually located within one lobe) were compared to the ECDs. Results: All interictal scalp EEG demonstrated almost continuous spike wave activity in the area of the CD. In FCD prior to the clinical onset, there was a generalised attenuation of spike wave, followed by an increase in amplitude and frequency of the focal epileptiform activity. In ECDs, seizure onset was characterised by bursts of generalised discharges (of higher amplitude in the affected hemisphere), with intermittent attenuation of activity as the seizure evolved. Subdural interictal EEG findings in FCD, demonstrated spikes from the area of CD with bursts of high frequency (>40Hz) at what proved at surgery to be the edge of the CD . Prior to the clinical seizure onset, there where runs of low amplitude high frequency (>40Hz) activity, then runs of spike and wave of increasing amplitude and frequency, as the clinical seizure evolved. There is a strong relationship in FCD between attenuation in scalp recording and fast frequency seen subdurally. Conclusion: CD has distinctive electrographic patterns particuarly where focal. Such findings may have implications in surgical decision-making, and improve understanding of the underlying epileptogenicity in CD of childhood.