Seizure Reduction Likely With Surgery in Nonlesional Neocortical Epilepsy

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Presence of aura was found to be an independent prognostic factor of surgical outcomes.
Presence of aura was found to be an independent prognostic factor of surgical outcomes.

Patients with nonlesional neocortical epilepsy may benefit from epilepsy surgery, especially those who undergo complete resection of areas of high ictal and interictal activity, according to research published in JAMA Neurology.1

Previous identification of predictive factors of surgical outcomes in this population2 has helped identify surgical candidates in whom seizure semiology and presurgical evaluations fail to identify epileptogenic regions; however, there is little research on long-term surgical outcomes in this group.

In this study, researchers led by Dong Wook Kim, MD, PhD, from Konkuk University School of Medicine, Seoul, Korea, sought to evaluate long-term surgical outcomes in patients with nonlesional neocortical epilepsy and to identify characteristics predictive of positive outcomes.

The researchers enrolled 109 patients (64 men, 45 women; mean age, 27.1 years) with treatment-resistant neocortical epilepsy with no identifiable lesions on magnetic resonance imaging. All participants underwent focal surgical resection with information available for 10 to 21 years of follow-up (1 patient was lost to long-term follow-up because of unrelated death). All patients had undergone previous treatment with at least 2 failed antiepileptic drugs.

Presurgical evaluations included standard brain magnetic resonance imaging (n = 109), fluorodeoxyglucose–positron emission tomography (FDG-PET; n = 99), ictal single-photon emission computed tomography (SPECT; n = 71), and interictal and ictal scalp electroencephalography (EEG; n = 109). Factors including age at surgery, age of onset, duration of epilepsy, monthly seizure frequency, location of epileptogenic foci, aura, and data from FDG-PET, ictal SPECT, interictal EEG, ictal EEG, and intracranial EEG were evaluated for their prognostic role.

One year postsurgery, 54.1% of patients (59/109) had achieved seizure freedom, and another 33.9% experienced notable improvement in seizure frequency. Forty-seven of the 59 patients who experienced seizure freedom had a history of aura before surgery, and 17 experienced persistent aura postsurgery. Four of these patients reported loss of aura over the course of follow-up, and 2 experienced an early recurrence of seizure. At 10-year follow-up, 59.3% of patients reported seizure freedom and 29.6% reported a considerate improvement in seizure frequency. Data from the final follow-up with each patient indicated that 59.3% had achieved seizure freedom and 30.6% experienced notable improvement in seizure frequency. All antiepileptic drugs were stopped in 23 of 64 patients at last follow-up, with no seizure recurrence. Overall, changes in postoperative status were less frequent compared with in patients with mesial temporal lobe epilepsy.

After univariate analysis, localizing patterns in FDG-PET (odds ratio [OR], 0.30; 95% confidence interval [CI], 0.14-0.66) and ictal SPECT (OR, 0.37; 95% CI, 0.15-0.87), high concordance (≥2) in noninvasive presurgical evaluations (OR, 3.15; 95% CI, 1.42-7.02), and complete resection of areas of ictal onset with frequent interictal spikes observed during intracranial EEG (OR, 0.39; 95% CI, 0.17-0.90) were significant predictors of surgical outcomes at 1 year; however, the factors were not predictive of seizure freedom in multivariate analysis. At 10-year follow-up, aura (OR, 2.52; 95% CI, 1.12-5.68), higher concordance (≥2) in presurgical evaluations (OR, 2.41; 95% CI, 1.09-5.33), and complete resection of areas of ictal onset with frequent interictal spikes (OR, 0.40; 95% CI, 0.18-0.92) were significant predictors of surgical outcomes. Presence of aura remained a significant independent prognostic factor after multivariate analysis. At last follow-up, the presence of aura (OR, 3.48; 95% CI, 1.46-8.28) and complete resection of areas of ictal onset with frequent interictal spikes (OR, 0.37; 95% CI, 0.15-0.91) remained significant independent prognostic factors after multivariate analysis.

"Although patients with nonlesional neocortical epilepsy have not been considered as optimal candidates for surgical treatment, recent survey studies showed that there is a strong shift toward a greater proportion of surgery for nonlesional neocortical epilepsy," the authors wrote. In this study, the "chance of seizure freedom was lower than those of [mesial temporal lobe epilepsy] and lesional neocortical epilepsy; however, it was notable that nearly 90% of patients benefited from resection surgery for nonlesional neocortical epilepsy."

In addition, the predictive factors identified in this study may help identify potential candidates for resective surgery.

In reporting their results, the authors noted several limitations, including the small number of participants, the long inclusion period, and the possibility of selection bias.

References

  1. Kim DW, Lee SK, Moon H, Jung K, Chu K, Chung C. Surgical treatment of nonlesional neocortical epilepsy: Long-term longitudinal study [published online January 3, 2017]. JAMA Neurol. doi: 10.1001/jamaneurol.2016.4439
  2. Lee SK, Lee SY, Kim KK, Hong KS, Lee DS, Chung CK. Surgical outcome and prognostic factors of cryptogenic neocortical epilepsy. Ann Neurol. 2005;58:525-532
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