INTRACRANIAL EEG SEIZURE-ONSET PATTERNS AND SURGICAL OUTCOMES IN PATIENTS WITH REFRACTORY EPILEPSY [P08.064]
Tarek Zakaria, Terrence Lagerlund, Elson So, Gregory Worrell, Rochester, MN Intracranial electroencephalography (iEEG) ictal-onset patterns may help to identify patients who are likely to have good clinical outcomes after epilepsy surgery, according to this retrospective study of 61 surgical patients. Several previous studies have attempted to identify patient factors that predict clinical outcomes following epilepsy surgery. Factors that were found to predict better surgical outcomes have included absence of generalized tonic clonic seizures, the extent to which epileptic EEG activity is restricted to a particular focus, mesial temporal sclerosis (MTS), the presence of a focal lesion on magnetic resonance imaging (MRI), and correct localized hypometabolism on fluorodeoxyglucose positron emission tomography.1-3 Although iEEG is widely used in the preoperative assessments of some patients with medically refractory epilepsy, it has actually been reported to be associated with poorer outcomes.4
In this study, Zakaria et al continued to probe and refine the relationship between clinical outcomes following epilepsy surgery and ictal-onset patterns using iEEG. iEEG seizure recordings were retrospectively examined for a total of 196 seizure episodes that were obtained from 61 medically refractory patients who underwent surgery for epilepsy involving the temporal (22 patients), frontal (29 patients), parietal (6 patients), or occipital (4 patients) lobes. Most of the patients had MRI evidence of pathology, including nonspecific gliosis, MTS, cortical dysplasia, or tumor. Seizure discharges were categorized on the basis of frequency, morphology, and spatial distribution of seizure activity. Patients were followed for 1 to 7 years after surgery.
Surgical outcomes were rated using the International League Against Epilepsy rating scale, with a good surgical result defined as postsurgical Class 1 (seizure-free and no auras for 2 years with no more than a few postoperative seizures), Class 1a (seizure-free since surgery with no auras), Class 2 (only auras, no seizures), or Class 3 (no more than 1–3 seizure days per year; may have auras).5 A good surgical outcome was noted for 42 of the 61 patients (68%). Surgical outcome was not significantly associated with patient age, sex, or the location of the seizure focus. An ictal-onset pattern characterized by low-voltage fast activity was associated with a high success rate (90.9% of patients), whereas fewer patients who exhibited a pattern of rhythmic sinusoidal or spike waves had good surgical outcomes (56.4%; P = .005). The likelihood of a successful outcome was also better for patients with ictal-onset rhythm of γ or β frequency (>12 Hz). An ictal onset with a relatively restricted distribution (≤5 electrodes) tended to predict a greater likelihood of a good outcome, although this relationship was not statistically significant.
The results of this study suggest that certain iEEG ictal-onset parameters may identify patients who are especially likely to experience good outcomes following epilepsy surgery. Good surgical outcome appears to be more likely in patients with high frequency ictal onset and possibly with a more focal spatial distribution.
References
1. Spencer SS, Berg AT, Vickrey BG, et al. Predicting long-term seizure outcome after resective epilepsy surgery: the multicenter study. Neurology. 2005;65:912-918.
2. Berg AT, Walczak T, Hirsch LJ, Spencer SS. Multivariable prediction of seizure outcome one year after resective epilepsy surgery: development of a model with independent validation. Epilepsy Res. 1998;29:185-194.
3. Yun CH, Lee SK, Lee SY, et al. Prognostic factors in neocortical epilepsy surgery: multivariate analysis. Epilepsia. 2006;47:574-579.
4. Tonini C, Beghi E, Berg AT, et al. Predictors of epilepsy surgery outcome: a meta-analysis. Epilepsy Res. 2004;62:75-87.
5. Wieser HG, Blume WT, Fish D, et al. ILAE commission report: proposal for a new classification of outcome with respect to epileptic seizures following epilepsy surgery. Epilepsia. 2001;42:282-286.
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