Abstracts

Rationale: Polymicrogyria (PMG) is a heterogeneous and highly epileptogenic malformation of cortical development. The potential role of epilepsy surgery in patients with PMG has been increasingly recognized. In the PMG cohort of patients from the Epilepsy Phenome/Genome Project (EPGP), we sought to evaluate whether the predicted region of seizure onset based on seizure semiology and EEG data corresponded to the location of the PMG seen on MRI. In addition, we assessed the outcomes of epilepsy surgery in the subgroup of patients for whom this was performed. Methods: Participants were recruited through EPGP, a multi-center collaborative including 26 sites from the United States, Argentina, Australia, and New Zealand. Detailed phenotypic data were reviewed for all patients with epilepsy and PMG. Epilepsy lateralization was assessed using EEG and seizure semiology, and then compared to MRI to establish concordance. In patients who underwent epilepsy surgery, we evaluated outcomes at last follow-up. Results: We identified 90 patients (43 female) with PMG and epilepsy. The cohort included pediatric and adult patients with a median age of 11 years (<1-55). Most patients presented with localization-related epilepsy (64.4%); complex partial seizures were the most common seizure type (50%). Half of the patients had bilateral PMG on MRI (50%). Of the 45 unilateral cases, 17 (37.8%) were located in the left hemisphere and 28 (62.2%) were located in the right hemisphere. When comparing PMG and epilepsy lateralization, 70.6% of the 17 patients with left-sided malformations had concordant data suggesting they might be potential candidates for surgery. From this group, one participant underwent epilepsy surgery. Of the 28 patients with right-sided malformations, 75% had right-sided seizure onset with 4 undergoing epilepsy surgery. One patient with bilateral/multifocal epilepsy also underwent epilepsy surgery. Among the patients with bilateral PMG, 15.6% had seizure onset on the right, 15.6% on the left, 35.6% bilateral/multifocal, and 11.1% generalized with 3 patients from this group undergoing epilepsy surgery (2 right, 1 left, see figure). In total, 9 patients in our series underwent epilepsy surgery. They presented with a range of seizure semiologies and did not have strictly focal or unilateral malformations. After surgery, 7 patients had major improvement (Engel score I), 1 patient had overall worsening of seizures (Engel score IV), and 1 patient was seizure-free but had insufficient follow-up for Engel scoring. Conclusions: The majority of the EPGP cohort with PMG and epilepsy were found to have concordance between laterality of PMG and predicted region of seizure onset based on seizure semiology and EEG data. Our data from the subset of patients who underwent epilepsy surgery suggest that surgery can be successful for carefully selected patients with PMG. Future phenotypic analysis with the addition of genotypic data may provide further insight into the prediction of surgical candidacy among patients with PMG and epilepsy.