Abstracts

Rationale: Focal cortical dysplasia (FCD) is a common cause of pharmacoresistant epilepsy. The pathological mechanisms, clinical and EEG characteristics of the subtypes of FCD are not fully understood. In this study we reviewed the invasive EEG data and clinical characteristics of patients with refractory epilepsy due to FCD who underwent epilepsy surgery at Cleveland Clinic Epilepsy Center. The purpose of this study was to evaluate possible correlations between the subtypes of FCD and EEG electrocorticographic patterns by using invasive electrodes (subdural grids, depths, or stereotactic electrodes), and clinical data as epilepsy duration, age of onset of epileptic seizures, epilepsy risk factors and frequency of seizures. Methods: We retrospectively reviewed EEG characteristics and clinical data of patients with various FCD subtypes (ILAE Classification of 2011) who underwent invasive evaluation with intracranial electrodes before surgical resection at the Cleveland Clinic Epilepsy Center between 1999 and 2011. Only patients with the histological diagnosis of FCD who underwent invasive EEG evaluation were included in the study (n = 139). Regarding to the electrocorticographic recordings, we considered basically paroxysmal fast activity versus repetitive spikes for ictal EEG onset and isolated spikes, repetitive spikes, or paroxysmal fast activity for interictal activities. Results: FCD Type I was the more frequent subtype of FCD in temporal lobe (p=0.002). Most patients with FCD Type I (78.7%) had no identifiable risk factors for epilepsy as compared to patients with other other subtypes (p=0.01). Patients with FCD Type I had later seizure onset (0.001) than patients with FCD types IIA, IIB or III. Seizure onset in patients with FCD type I was iat age 13.6 years old (SD=11.5) while patients with other subtypes of FCD had earlier seizures onset (mean 6.4 y, SD=4.9). We found no correlations between the type of ictal (p=0.86) or interictal EEG patterns recorded by electrocorticography (p=0.82). Duration of epilepsy (p=0.21) and frequency of seizures (p=0.20) did not correlate with FCD subtypes. Conclusions: We have found significant clinical correlations between the histophatologycal subtypes of FCD, as the presence of risk factor for epilepsy and the age of seizure onset. The EEG ictal and interictal patterns did not show significant differences among the subtypes of FCD. Our data suggest that there no signature EEG epileptic patterns of various FCD subtypes. Identifiable risk factors and earlier seizure onset were reported in non type I FCD. These results suggest significant pathobiological and clinical differences between type I and other FCD subtypes.