By Kimberly Pargeon, MD

Assistant Professor of Clinical Neurology, Weill Cornell Medical College

Dr. Pargeon reports no financial relationships relevant to this field of study.

SYNOPSIS: In this study of 109 consecutive patients with medically refractory neocortical epilepsy without MRI-identifiable lesions who underwent focal resection at a single hospital from 1995 to 2005, almost 60% of patients achieved long-term seizure freedom, with anti-epileptic drugs being withdrawn successfully in about a third of these patients.

SOURCE: Kim DW, Lee SK, Moon HJ, et al. Surgical treatment of nonlesional neocortical epilepsy: Long-term longitudinal study. JAMA Neurol 2017;74:324-331.

For patients with medically refractory focal epilepsy, epilepsy surgery can be an important therapeutic option. The most successful surgical outcomes typically are seen with mesial temporal lobe epilepsy (mTLE), particularly where the ipsilateral mesial temporal structures appear atrophic with increased signal on MRI. However, in neocortical epilepsy, the same tools used for localizing the epileptogenic onset zone in mTLE can be less helpful, so not surprisingly, patients with MRI-identifiable lesions are offered surgical resection more often than those without and typically with more satisfactory outcomes.1 Kim et al were interested in the surgical outcomes for patients with medically refractory neocortical epilepsy without MRI-identifiable lesions and in identifying potential prognostic factors.

The authors identified 109 consecutive patients at a single hospital in Seoul, South Korea, with medically refractory neocortical epilepsy without MRI-identifiable lesions who underwent focal surgical resection from 1995 to 2005. Patients consisted of 64 males (59%), ranging in age from 7-56 years with an average age of seizure onset of 13.6 years (SD, 7.6 years) and average seizure duration of 13.4 years (SD, 7.3 years). All patients underwent a brain MRI (up to 1.5T), and most patients underwent a FDG-PET scan (90%) and/or a SPECT scan (65%, both ictal and interictal). All patients underwent interictal and ictal scalp EEG monitoring with additional anterior temporal electrodes, and also later underwent intracranial EEG monitoring with a combination of implanted grids and strips, with placement based on their presurgical evaluation.

Follow-up data were available for at least 10 years for all but one patient. Localizations were as follows: 39 frontal, 44 neocortical temporal, 12 parietal, 13 occipital, and one multifocal. The most common pathological finding was focal cortical dysplasia in 60%, followed by nonspecific gliosis (13%). At one year post-surgery, 54.1% achieved seizure freedom (Engel class I) with an additional 33.9% achieving a “worthwhile” improvement (Engel class II or III). There were no significant changes at 10 years, with 59.3% reporting seizure freedom and an additional 30.6% achieving a worthwhile improvement. Of the patients achieving seizure freedom at 10 years, all anti-seizure medications were withdrawn successfully without seizure recurrence in 35.9% at last follow-up.

The authors also looked at prognostic factors that may predict better surgical outcomes. On univariate analysis, localizing patterns on other imaging tests (FDG-PET and ictal SPECT), “high” concordance in noninvasive presurgical evaluations, and complete resection of the region of ictal onset on intracranial monitoring were significant prognostic factors at year 1; however, none of these was an independent predictor of seizure freedom in the multivariate analysis. At year 10, presence of aura, higher concordance of presurgical data, and complete resection of the area of ictal onset on intracranial monitoring were significant prognostic factors, with the presence of aura remaining as the only independent prognostic factor on multivariate analysis. Findings were comparable at last follow-up, except complete resection of the region of ictal onset also was an independent prognostic factor on multivariate analysis.

COMMENTARY

In cases of medically refractory focal epilepsy, the ultimate goal is to offer patients potentially curative surgery. However, we often struggle with how to identify which patients may be the most “ideal” candidates and how to predict the likelihood of seizure freedom for individual patients. Kim et al attempted to address these issues for a group of patients many neurologists have determined are poor surgery candidates. However, now that the cases of typical mTLE have declined, we are looking for other groups of patients in whom we can intervene surgically. In fact, a recent study showed that the annual rate of anterior temporal lobectomies for mesial temporal sclerosis decreased by more than 65% between 2006 and 2010 at level 3 and 4 epilepsy centers in the United States, with the annual rate of extratemporal surgery exceeding that for MTS as of 2008.1 Kim et al found that approximately 60% of patients with nonlesional neocortical epilepsy had long-term seizure freedom after resection at last follow-up, with about a third of those patients tolerating withdrawal of all anti-seizure medications without seizure recurrence. Another 30% of patients had some “worthwhile” improvement (Engel class II or III) at last follow-up. However, it should be noted that this study included a small number of patients at a single center. Although the follow-up period was prolonged at a minimum of 10 years, these findings are not reflective of newer, more modern diagnostic or surgical techniques, such as stereo EEG or more powerful MRIs (e.g., 3T). It may be reasonable to presume that these techniques only would improve the chances of success for future patients.

REFERENCE

  1. Kaiboriboon K, Malkhachroum AM, Zrik A, et al. Epilepsy surgery in the United States: Analysis of data from the National Association of Epilepsy Centers. Epilepsy Res 2015;116:105-109.