Ictal Scalp EEG in Mesial Temporal Lobe Epilepsy Patients with Unilateral versus Bilateral Interictal Epileptiform Discharges

BACKGROUND: Interictal and ictal scalp EEG is the most often used and relied-on method of noninvasive presurgical evaluation in temporal lobe epilepsy. We attempted to compare unitemporal interictal epileptiform discharges (UIED) with bitemporal interictal epileptiform discharges (BIED) groups for lateralizing value and propagation patterns of ictal scalp EEGs. METHODS: We investigated ictal scalp EEGs in 48 patients who had undergone anterior temporal lobectomies. We divided them into UIED and BIED groups by cut-off value of 90% in the laterality of IED. RESULTS: We analyzed ictal EEG patterns in 201 seizures of 32 patients with UIED and 86 seizures of 16 patients with BIED. Ictal scalp EEG was correctly lateralized significantly more often in the UIED group compared with the BIED group; 93.5% versus 57.0% in seizures and 93.8% versus 62.5% in patients, respectively. Bilateral independent onset was seen more frequently in the BIED group whereas the maintenance of ictal discharges in the unilateral temporal or hemisphere occurred more frequently in the UIED group. Lateralization by a later significant pattern (LSP) presents additional value of correct lateralization rather than pattern at onset (PAO) only. CONCLUSIONS: Interpretation of ictal scalp EEGs must be considered more cautiously in patients with BIED because BIED may be correlated with bitemporal excitability.

Predicting Factors of Long-term Surgical Outcome for Mesial Temporal Lobe Epilepsy with Unilateral Hippocampal Atrophy on MRI / 대한간질학회지

PURPOSE: To identify the clinical and electroencephalographic factors which are independently predictive of a postoperative seizure-free outcome for 4 years. We compared the outcomes of the first 2 years with the subsequent 2 years one after anterior temporal lobectomy (ATL) for mesial temporal lobe epilepsy (MTLE) with unilateral hippocampal atrophy (HA) on MRI. METHODS: We studied 51 consecutive operated patients who had above 4 years of follow-up and had MTLE with definite unilateral HA on MRI. The surgical outcome was classified as either seizure-free or not seizure-free in the first postoperative 2 years and the subsequent 2 years. Several clinical variables were included. The scalp EEG parameters included the lateralization of interictal epileptiform discharges, ictal onset location, ictal onset frequency, ictal EEG lateralization, and ictal scalp EEG propagation (bitemporal asynchrony or switch of lateralization). Variable factors were subjected to univariate analysis. RESULTS: Overall, 36 patients (71%) became seizure-free during the postoperative 4 years. On univariate analysis, only one factor was significantly associated with poor outcome (p<0.05): ictal scalp EEG propagation pattern such as bitemporal asynchrony or switch of lateralization. The seizure-free outcome was seen in 88.9% of patients without bitemporal asynchroncy, or switch of lateralization while only 54.5% of patients with those patterns (p=0.007) during the postoperative third and fourth year. However, those propagation patterns did not show the prognostic value during the first 2 years (p=0.449). Other variable factors were found not to be predictive of prognosis on early or late recurrence. CONCLUSIONS: Bitemporal asynchrony or a switch of lateralization in the ictal scalp EEG might be a highly predictive factor for an undesirable surgical outcome, late recurrence of seizure during a follow-up period after ATL, and probably an index of bitemporal epileptogenicity in MTLE.

Effect of Combination of Ictal Scalp EEG and Seizure Semiology on Seizure Lateralization in Temporal Lobe Epilepsy / 대한간질학회지

PURPOSE: To compare the reliability of lateralization between seizure semiology and ictal scalp EEG findings in mesial temporal lobe epilepsy (MTLE) patients, and to examine the advantage of the combined use of these two methods. METHODS: We independently reviewed the ictal scalp EEG recordings and clinical seizure semiology of 243 seizures recorded in 58 consecutive MTLE patients. All patients were seizure-free for at least 1 year postoperatively. Each seizure was lateralized on the basis of ictal semiology and ictal scalp EEG patterns according to strictly defined criteria, respectively. Individual patients were also lateralized based on these data. RESULTS: Seizure semiology analysis lateralized 64.6 % of seizures and 82.8 % of patients. Ictal scalp EEG analysis lateralized 74.5% of seizures and 74.1% of patients. Combination of the information from the two methods allowed for lateralization in a greater portion of both seizures (79.8%) and patients (89.7%). CONCLUSION: This study suggests that combination of ictal scalp EEG findings and seizure semiology improves the lateralization of individual seizures and patients. Therefore, it is worth lateralizing with standardized combined ictal EEG and semiology analysis for noninvasive presurgical evaluation in TLE patients.