On the prognostic value of ictal EEG patterns in temporal lobe epilepsy surgery: A cohort study

The value of ictal scalp EEG in focal epilepsies surgery: a retrospective analysis

OBJECTIVE

To describe the association between preoperative ictal scalp electroencephalogram (EEG) results and surgical outcomes in patients with focal epilepsies.

METHODS

The data of consecutive patients with focal epilepsies who received surgical treatments at our center from January 2012 to December 2021 were retrospectively analyzed.

RESULTS

Our data showed that 44.2% (322/729) of patients had ictal EEG recorded on video EEG monitoring during preoperative evaluation, of which 60.6% (195/322) had a concordant ictal EEG results. No significant difference of surgery outcomes between patients with and without ictal EEG was discovered. Among MRI-negative patients, those with concordant ictal EEG had a significantly better outcome than those without ictal EEG (75.7% vs. 43.8%, p = 0.024). Further logistic regression analysis showed that concordant ictal EEG was an independent predictor for a favorable outcome (OR = 4.430, 95%CI 1.175-16.694, p = 0.028). Among MRI-positive patients, those with extra-temporal lesions and discordant ictal EEG results had a worse outcome compared to those without an ictal EEG result (44.7% vs. 68.8%, p = 0.005). Further logistic regression analysis showed that discordant ictal EEG was an independent predictor of worse outcome (OR = 0.387, 95%CI 0.186-0.807, p = 0.011) in these patients. Furthermore, our data indicated that the number of seizures was not associated with the concordance rates of the ictal EEG, nor the surgical outcomes.

CONCLUSIONS

The value of ictal scalp EEG for epilepsy surgery varies widely among patients. A concordant ictal EEG predicts a good surgical outcome in MRI-negative patients, whereas a discordant ictal EEG predicts a poor postoperative outcome in lesional extratemporal lobe epilepsy.

Distribution of postictal slowing has an additional yield to interictal epileptiform discharge in predicting surgical outcomes in temporal lobe epilepsy

OBJECTIVE

To investigate whether the slowing of bilateral postictal scalp electroencephalography (EEG) after focal impaired awareness seizures is associated with poor seizure outcomes after temporal lobe epilepsy (TLE) surgery.

METHODS

This retrospective cohort study was conducted in the Department of Epileptology, Tohoku University Hospital from 2010 to 2020. The study included 42 patients with TLE who underwent a detailed presurgical evaluation and sequential resective surgery for the unilateral probable epileptogenic temporal lobe with 1 year or more of follow-up. We reviewed the interictal epileptiform distribution and those of the ictal and postictal epochs of the first focal impaired awareness seizure recorded in presurgical scalp EEG. We classified patients either with postoperative seizure-free status (Engel I) as group A or those with seizure persistence (Engel II-IV) as group B.

RESULTS

Of 42 patients, 29 (69%) were classified into group A. Compared with group B, group A had a lower number of bilateral postictal polymorphic delta activity (PPDA) (10.3%: 61.5%) and bilateral interictal epileptiform discharges (IEDs) (13.8%: 69.2%) (P = 0.003, P = 0.001, respectively). A combined analysis of bilateral PPDA and IEDs per individual patient showed significantly more frequent seizure persistence after surgery (P < 0.0001) than a single analysis of bilateral IEDs or PPDA alone (P = 0.001). The regression analysis revealed that bilaterally distributed PPDA or IEDs had 13.50 or 13.72 times higher odds of persisting seizures within 1 year of surgery (95% confidence interval: 1.90-95.88; 2.12-88.87, respectively) (P = 0.009, 0.006).

SIGNIFICANCE

The results of this study revealed that the bilateral distribution of PPDA was associated with poor postoperative seizure outcomes in patients with TLE, as well as bilateral IEDs. Additionally, the concomitant bilateral distribution of interictal and postictal changes is a strong indicator of poor surgical outcomes.

Semiology, EEG, and neuroimaging findings in temporal lobe epilepsies

Temporal lobe epilepsy (TLE) is the most common type of focal epilepsy. First descriptions of TLE date back in time and detailed portraits of epileptic seizures of temporal origin can be found in early medical reports as well as in the works of various artists and dramatists. Depending on the seizure onset zone, several subtypes of TLE have been identified, each one associated with peculiar ictal semiology. TLE can result from multiple etiological causes, ranging from genetic to lesional ones. While the diagnosis of TLE relies on detailed analysis of clinical as well as electroencephalographic (EEG) features, the lesions responsible for seizure generation can be highlighted by multiple brain imaging modalities or, in selected cases, by genetic investigations. TLE is the most common cause of refractory epilepsy and despite the great advances in diagnostic tools, no lesion is found in around one-third of patients. Surgical treatment is a safe and effective option, requiring presurgical investigations to accurately identify the seizure onset zone (SOZ). In selected cases, presurgical investigations need intracerebral investigations (such as stereoelectroencephalography) or dedicated metabolic imaging techniques (interictal PET and ictal SPECT) to correctly identify the brain structures to be removed.

Prognostic factors of postoperative seizure outcome in patients with temporal lobe epilepsy and normal magnetic resonance imaging

PURPOSE

To retrospectively analyse a single-centre consecutive surgical series of patients with temporal lobe epilepsy (TLE) and negative MRI. To identify factors associated with postoperative seizure outcome among several presurgical, surgical and postsurgical variables.

METHODS

Clinical records of 866 patients who received temporal lobe resections and with a minimum follow-up of 12 months were retrospectively searched for MRI-negative cases. Anamnestic, clinical, neurophysiological, surgical, histopathological and postsurgical data were collected. Seizure outcome was categorised as favourable (Engel's class I) and unfavourable (Engel's classes II-IV). Uni- and multivariate statistical analysis was performed to identify variables having a significant association with seizure outcome.

RESULTS

Forty-eight patients matched the inclusion criteria. 26 (54.1%) patients required invasive EEG evaluation with Stereo-electro-encephalography (SEEG) before surgery. Histological evaluation was unremarkable in 34 cases (70.8%), revealed focal cortical dysplasias in 13 cases and hippocampal sclerosis in 2. 28 (58.3%) patients were in Engel's class I after a mean follow-up of 82 months (SD ± 74; range 12-252). Multivariate analysis indicated auditory aura, contralateral diffusion of the discharge at Video-EEG monitoring and use of ¹⁸F-FDG PET as variables independently associated with seizure outcome.

CONCLUSION

Carefully selected patients with MRI-negative TLE can be good candidates for surgery. Surgery should be considered with caution in patients with clinical features of neocortical seizure onset and contralateral propagation of the discharge. Use of ¹⁸F-FDG PET may be helpful to improve SEEG and surgical strategies. The presented data help in optimising the selection of patients with MRI-negative TLE with good chances to benefit from surgery.

Focal epilepsies and focal disorders

Electroencephalographic (EEG) investigations are crucial in the diagnosis and management of patients with focal epilepsies. EEG may reveal different interictal epileptiform discharges (IEDs: abnormal spikes, sharp waves). The EEG visibility of a spike depends on the surface area of cortex involved (>10cm²) and the brain localization of cortical generators. Regions generating IEDs (defining the "irritative zone") are not necessarily equivalent to the seizure onset zone. Focal seizures are dynamic processes originating from one or several brain regions (that generate fast oscillations and are called the epileptogenic zone) before spreading to other structures (that generate lower frequency oscillations and are called the propagation zone). Several factors limit the expression of seizures on scalp EEG, such as the area involved, degree of synchronization, and depth of the cortical generators. Different scalp EEG seizure onset patterns may be observed: fast discharge, background flattening, rhythmic spikes, sinusoidal discharge, or sharp activity. However, to a large extent EEG changes are linked to seizure propagation. Finally, in the context of presurgical evaluation, the combination of interictal and ictal EEG features is crucial to provide an optimal hypothesis concerning the epileptogenic zone.

Unusual ictal propagation patterns suggesting poor prognosis after temporal lobe epilepsy surgery: Switch of lateralization and bilateral asynchrony

OBJECTIVE

The objective of this study was to investigate unusual ictal propagation patterns in patients with drug-resistant temporal lobe epilepsy (TLE) and reveal their electrophysiological, neuroimaging, and prognostic properties after surgery.

METHODS

Among 248 patients with TLE who underwent scalp video-electroencephalographic (EEG) monitoring, 24 patients with 'switch of lateralization' or 'bilateral asynchrony' in at least one of their seizures (9.3%) were analyzed retrospectively. The postoperative outcome was determined in 16 patients who had undergone epilepsy surgery.

RESULTS

All but 5 of the included patients had hippocampal sclerosis (HS) as their magnetic resonance imaging (MRI) findings. Twelve out of 16 patients (75%) who had surgery were seizure-free for at least 1 year. Nine out of 12 patients (75%) with good outcome had unilateral interictal EEG discharges in temporal regions whereas 3 out of 4 patients with poor outcome had bilateral temporal interictal spiking (p = 0.018).

CONCLUSION

Unusual ictal propagation patterns are not always related to poor prognosis after surgery in patients with TLE. Patients with unilateral interictal spiking in the temporal region tend to have good outcome despite these unusual patterns. These patterns can also be seen in patients with TLE with other etiologies besides the well-known HS in MRI.

Long-term seizure outcome for international consensus classification of hippocampal sclerosis: a survival analysis

PURPOSE

Surgery is regarded as a common treatment option for patients with mesial temporal lobe epilepsy (MTLE) as a result of hippocampal sclerosis (HS). However, approximately one-third of patients with intractable epilepsy did not become seizure-free after tailored resection strategies. It would be compelling to identify predictive factors of postoperative seizure outcomes. Our aim was to assess the correlation between HS classification and long-term postoperative seizure outcome in patients with MTLE due to HS.

METHODS

To investigate HS classification, semi-quantitative analysis and immunohistochemical staining of neuronal nuclei (NeuN) were performed on 100 postoperative hippocampal specimens. All patients had a 1-7 year postoperative follow-up. The postoperative seizure outcome was evaluated using International League Against Epilepsy (ILAE) outcome classification.

RESULTS

Three types of HS were recognized. The highest incidence of initial precipitating injury (IPI) was noted in the HS ILAE type 1 group (53.1%). The most favorable long-term seizure outcome was also noted in the HS ILAE type 1 group. The shortest epilepsy duration was recorded in the HS ILAE type 2 group (mean epilepsy duration=6.64 ± 5.83 years). The completely seizure free rate of patients in all groups declined with an increase in time.

CONCLUSIONS

Our study for the first time demonstrated a significant correlation between HS ILAE types and long-term postoperative seizure outcome in patients with MTLE due to HS. Therefore, HS ILAE types have predictive value in long-term seizure outcome following epilepsy surgery.