Clinical differences in patients with unilateral hippocampal sclerosis and unitemporal or bitemporal epileptiform discharges

Ipsilateral preictal alpha rhythm attenuation (IPARA): An EEG sign of side of seizure onset in temporal lobe epilepsy

PURPOSE

Identification of the seizure onset zone is critically important for outlining the surgical plan in the treatment of pharmacoresistant focal epilepsy. In patients with temporal lobe epilepsy (TLE), bilateral ictal scalp EEG changes frequently occur and can make lateralization of the seizure onset zone difficult. We investigated the incidence and clinical utility of unilateral preictal alpha rhythm attenuation as a lateralizing sign of seizure onset in TLE.

METHODS

Scalp EEG recordings of the seizures acquired during presurgical video-EEG monitoring of 57 consecutive patients with TLE were reviewed retrospectively. Included patients had interictal baseline recordings demonstrating symmetrical posterior alpha rhythm and seizures occurring during wakefulness.

RESULTS

We identified a total of 649 seizures in the 57 patients, of which 448 seizures in 53 patients fulfilled the inclusion criteria. Among the 53 included patients, 7 patients (13.2%) exhibited a distinct attenuation of the posterior alpha rhythm prior to the first ictal EEG changes, in 26 of 112 (23.2%) included seizures. Preictal alpha rhythm attenuation in these seizures was ipsilateral to the ultimately determined side of seizure onset (based on video-EEG or intracranial EEG findings) in 22 (84.6%) of these seizures and bilateral in 4 (15.4%), and occurred on average 5.9 ± 2.6 s prior to ictal EEG onsets.

CONCLUSION

Our findings suggest that in some patients with TLE lateralized preictal attenuation of the posterior alpha rhythm may be a useful indicator of side of seizure onset, presumably due to early disruption of thalamo-temporo-occipital network function, likely mediated through the thalamus.

Vagus nerve stimulation for pharmacoresistant epilepsy secondary to encephalomalacia: A single-center retrospective study

Objective

Vagus nerve stimulation (VNS) is an adjunctive treatment for pharmacoresistant epilepsy. Encephalomalacia is one of the most common MRI findings in the preoperative evaluation of patients with pharmacoresistant epilepsy. This is the first study that aimed to determine the effectiveness of VNS for pharmacoresistant epilepsy secondary to encephalomalacia and evaluate the potential predictors of VNS effectiveness.

Methods

We retrospectively analyzed the seizure outcomes of VNS with at least 1 year of follow-up in all patients with pharmacoresistant epilepsy secondary to encephalomalacia. Based on the effectiveness of VNS (≥50% or <50% reduction in seizure frequency), patients were divided into two subgroups: responders and non-responders. Preoperative data were analyzed to screen for potential predictors of VNS effectiveness.

Results

A total of 93 patients with epilepsy secondary to encephalomalacia who underwent VNS therapy were recruited. Responders were found in 64.5% of patients, and 16.1% of patients achieved seizure freedom at the last follow-up. In addition, the responder rate increased over time, with 36.6, 50.5, 64.5, and 65.4% at the 3-, 6-, 12-, and 24-month follow-ups, respectively. After multivariate analysis, seizure onset in adults (>18 years old) (OR: 0.236, 95%CI: 0.059-0.949) was found to be a positive predictor, and the bilateral interictal epileptic discharges (IEDs) (OR: 3.397, 95%CI: 1.148-10.054) and the bilateral encephalomalacia on MRI (OR: 3.193, 95%CI: 1.217-8.381) were found to be negative predictors of VNS effectiveness.

Conclusion

The results demonstrated the effectiveness and safety of VNS therapy in patients with pharmacoresistant epilepsy secondary to encephalomalacia. Patients with seizure onset in adults (>18 years old), unilateral IEDs, or unilateral encephalomalacia on MRI were found to have better seizure outcomes after VNS therapy.

Vagus nerve stimulation for refractory posttraumatic epilepsy: Efficacy and predictors of seizure outcome

Background

Traumatic brain injury (TBI) has been recognized as an important and common cause of epilepsy since antiquity. Posttraumatic epilepsy (PTE) is usually associated with drug resistance and poor surgical outcomes, thereby increasing the burden of the illness on patients and their families. Vagus nerve stimulation (VNS) is an adjunctive treatment for medically refractory epilepsy. This study aimed to determine the efficacy of VNS for refractory PTE and to initially evaluate the potential predictors of efficacy.

Methods

We retrospectively collected the outcomes of VNS with at least a 1-year follow-up in all patients with refractory PTE. Subgroups were classified as responders and non-responders according to the efficacy of VNS (≥50% or <50% reduction in seizure frequency). Preoperative data were analyzed to screen for potential predictors of VNS efficacy.

Results

In total, forty-five patients with refractory PTE who underwent VNS therapy were enrolled. Responders were found in 64.4% of patients, and 15.6% of patients achieved seizure freedom at the last follow-up. In addition, the responder rate increased over time, with 37.8, 44.4, 60, and 67.6% at the 3-, 6-, 12-, and 24-month follow-ups, respectively. After multivariate analysis, generalized interictal epileptic discharges (IEDs) were found to be a negative predictor (OR: 4.861, 95% CI: 1.145–20.632) of VNS efficacy.

Conclusion

The results indicated that VNS therapy was effective in refractory PTE patients and was well tolerated over a 1-year follow-up period. Patients with focal or multifocal IEDs were recognized to have better efficacy after VNS therapy.

Clinical significance of bilateral epileptiform discharges in temporal lobe epilepsy

OBJECTIVE

The aim of the current study was to investigate the rate and clinical significance of bitemporal interictal epileptiform discharges (IEDs) in a large cohort of patients with temporal lobe epilepsy (TLE).

METHODS

The data used in this study were collected at the Epilepsy Care Unit, Namazi Hospital, Shiraz University of Medical sciences, Shiraz, Iran, from 2008 to 2020. Inclusion criteria were a confirmed diagnosis of TLE based on the clinical grounds (history and the described seizure semiology) and a 2-hour interictal video-electroencephalography (EEG) monitoring. The EEG recording of each patient included both sleep (about 90 minutes) and wakefulness (about 30 minutes).

RESULTS

532 patients were included in this study [420 patients (79%) had unilateral IEDs, and 112 patients (21%) had bilateral IEDs]. Patients with bilateral IEDs less often had auras with their seizures and had higher frequencies of seizures (as a trend for focal to bilateral tonic-clonic seizures and significantly in focal seizures with impaired awareness) compared with those who had unilateral IEDs. Patients with bilateral epileptiform discharges showed a trend to experiencing ictal injury more frequently. Brain MRI findings were different between these two groups (p = 0.0001).

CONCLUSION

It is important to recognize that a patient with TLE has unilateral vs. bilateral IEDs. Bilateral IEDs in a patient with TLE may suggest a more severe disease (with a higher risk for ictal injuries and other significant consequences of frequent seizures). It may also suggest a somewhat different etiology.

Modulation of locomotor behaviors by location-specific epileptic spiking and seizures

INTRODUCTION

Epilepsy is a debilitating neurological condition characterized by spontaneous seizures as well as significant comorbid behavioral abnormalities. In addition to seizures, epileptic patients exhibit interictal spikes far more frequently than seizures, often, but not always observed in the same brain areas. The exact relationship between spiking and seizures as well as their respective effects on behavior are not well understood. In fact, spiking without overt seizures is seen in various psychiatric conditions including attention-deficit hyperactivity disorder.

METHODS

In order to study the effects of spiking and seizures on behavior in an epileptic animal model, we used long-term video-electroencephalography recordings at six cortical recording sites together with behavioral activity monitoring. Animals received unilateral injections of tetanus toxin into either the somatosensory or motor cortex.

RESULTS

Somatosensory cortex-injected animals developed progressive spiking ipsilateral to the injection site, while those receiving the injection into the motor cortex developed mostly contralateral spiking and spontaneous seizures. Animals with spiking but no seizures displayed a hyperactive phenotype, while animals with both spiking and seizures displayed a hypoactive phenotype. Not all spikes were equivalent as spike location strongly correlated with distinct locomotor behaviors including ambulatory distance, vertical movements, and rotatory movement.

CONCLUSIONS

Together, our results demonstrate relationships between brain region-specific spiking, seizures, and behaviors in rodents that could translate into a better understanding for patients with epileptic behavioral comorbidities and other neuropsychiatric disorders.

A cynomolgus monkey model of temporal lobe epilepsy

Temporal lobe epilepsy (TLE) with hippocampal sclerosis is the most common type of drug-resistant epilepsy. Non-human primates are attractive models for studying the pathogenic mechanisms of TLE, with the goal of developing new drugs and interventions. In this study, we developed and tested a Cynomolgus monkey (Macaca fascicularis) model of TLE. A total of 5 Cynomolgus monkeys received3-4 weekly unilateral hippocampal injections of kainic acid (KA) to induce repetitive acute seizures. Animals were monitored via video and electroencephalography (EEG) to assess KA-induced acute seizures and subsequent spontaneous recurrent epileptiform discharges (SREDs). During acute seizures, EEG recording showed bursts of generalized spike discharges arising from the temporal lobe ipsilateral to the KA injection. Three months later, we detected abundant interictal epileptiform discharges (IEDs) during pentobarbital induced anesthesia. Furthermore, two monkeys exhibited synchronized epileptiform discharges accompanied by symptoms mimicking absence seizures. No obvious convulsive symptoms were observed in any monkeys. Overall, our data indicate successful development of a Cynomolgus monkey model of TLE via unilateral hippocampal injection of KA.

Establishment of a rhesus monkey model of chronic temporal lobe epilepsy using repetitive unilateral intra-amygdala kainic acid injections

OBJECTIVE

Temporal lobe epilepsy (TLE) is a common type of acquired epilepsy refractory to medical treatment. As such, establishing animal models of this disease is critical to developing new and effective treatment modalities. Because of their small head size, rodents are not suitable for comprehensive electroencephalography (EEG) evaluation via scalp or subdural electrodes. Therefore, a larger primate model that closely recapitulates signs of TLE is needed; here we describe a rhesus monkey model resembling chronic TLE.

METHODS

Eight monkeys were divided into two groups: kainic acid (KA) group (n=6) and saline control group (n=2). Intra-amygdala KA injections were performed biweekly via an Ommaya device until obvious epileptiform discharges were recorded. Video-EEG recording was conducted intermittently throughout the experiment using both scalp and subdural electrodes. Brains were then analyzed for Nissl and glial fibrillary acid protein (GFAP) immunostaining.

RESULTS

After 2-4 injections of KA (approximately 1.2-2.4mg, 0.12-0.24mg/kg), interictal epileptiform discharges (IEDs) were recorded in all KA-treated animals. Spontaneous recurrent seizures (SRSs) accompanied by symptoms mimicking temporal lobe absence (undetectable without EEG recording), but few mild motor signs, were recorded in 66.7% (four of six) KA-treated animals. Both IEDs and seizures indicated a primary epileptic zone in the right temporal region and contralateral discharges were later detected. Segmental pyramidal cell loss and gliosis were detected in the brain of a KA-treated monkey.

CONCLUSIONS

Through a modified protocol of unilateral repetitive intra-amygdala KA injections, a rhesus monkey model with similar behavioral and brain electrical features as TLE was developed.

The medial temporal lobe epilepsy is a bilateral disease – novel aspects

Introduction.Medial temporal lobe epilepsy (MTLE) is the most frequent form of epilepsy in adulthood. It is classified as local/regional epilepsy. However, there is increasing evidence of the involvement of both temporal lobes and this provides abundant arguments to question this view, and consider MTLE as one of the typical bilateral system epilepsies.

Aim.To provide a contemporary review of medial temporal lobe epilepsy, discussing the bilateral aspects, with reference to epilepsy surgery.

Methods.A literature review and a resume of the author’s own experiences with MTLE patients.

Results.Recent electrophysiological and neuroimaging data provide convincing data supporting that MTLE is a bilateral disease. The uni-and bilateral features form a continuum and the participation rate of the two temporal lobes determine course and surgical perspective of the individual patient.

Conclusions.The contradictory data of invasive presurgical evaluations of MTLE patients suggest that there need to identify further indicatory markers of bilaterality and thus change the presurgical evaluation from the non-invasive towards the invasive ways. The mechanisms of the interrelationship between the two temporal lobes in MTLE warrants further research.

Interictal serum brain-derived neurotrophic factor level reflects white matter integrity, epilepsy severity, and cognitive dysfunction in chronic temporal lobe epilepsy

OBJECTIVE

Most patients with temporal lobe epilepsy (TLE) have epileptic foci originating from the medial temporal lobe, particularly the hippocampus. Brain-derived neurotrophic factor (BDNF) is a member of the neurotrophin growth factor mainly expressed in the hippocampus, though it is not known whether the circulating level of BDNF reflects cognitive performance or white matter structural changes in chronic TLE.

METHODS

Thirty-four patients with TLE and 22 healthy controls were enrolled for standardized cognitive tests, diffusion tensor imaging, and serum BDNF measurement. The patients were further divided into a subgroup with unilateral TLE (n=23) and a subgroup with bilateral TLE (n=11) for clinical and neuroimaging comparisons.

RESULTS

There were significantly lower BDNF levels in the patients with TLE compared with the controls, with significance contributed mainly from the subgroup with bilateral TLE, which also had more frequent seizures. The BDNF levels correlated with epilepsy duration (σ=-0.355; p=0.040) and fractional anisotropy (FA) in the left temporal lobe, left thalamus, and right hippocampus. Using a regression model, BDNF level predicted verbal memory score. Further, design fluency scores were predicted by serum BDNF level via the interactions with left temporal FA.

CONCLUSIONS

Serum BDNF levels reflected longer epilepsy duration, impaired white matter integrity, and poor cognitive function in patients with chronic TLE.

Contralateral interictal spikes are related to tapetum damage in left temporal lobe epilepsy

OBJECTIVE

In temporal lobe epilepsy (TLE), the epileptogenic focus is focal and unilateral in the majority of patients. A key characteristic of focal TLE is the presence of subclinical epileptiform activity in both the ictal and contralateral "healthy" hemisphere. Such interictal activity is clinically important, as it may reflect the spread of pathology, potentially leading to secondary epileptogenesis. The role played by white matter pathways in this process is unknown.

METHODS

We compared three interhemispheric white matter tracts (anterior commissure, fornix, and tapetum) to determine the pathway most associated with the presence of contralateral interictal spikes. Forty patients with unilateral left or right TLE were categorized based on the presence or absence of contralateral interictal spikes. Analyses of variance (ANOVAs) were run on diffusion properties from each tract.

RESULTS

The analyses revealed that patients with left TLE and with bilateral interictal spikes had lower fractional anisotropy (FA) and higher mean diffusivity (MD) in the tapetum. Patients with right TLE did not show this effect. No significant associations with bilateral activity were observed for the other tracts. Blood oxygen level-dependent (BOLD) functional connectivity data revealed that homotopic lateral, not mesial, temporal areas were reliably correlated in bilateral patients, independent of ictal side.

SIGNIFICANCE

Our results indicate that, among the tracts investigated, only the tapetum was associated with contralateral epileptiform activity, implicating this structure in seizures and possible secondary epileptogenesis. We describe two mechanisms that might explain this association (the interruption of inhibitory signals or the toxic effect of carrying epileptiform signals toward the healthy hemisphere), but also acknowledge other rival factors that may be at work. We also report that patients with TLE with bilateral spikes had increased lateral bitemporal lobe connectivity. Our current results can be seen as bringing together important functional and structural data to elucidate the basis of contralateral interictal activity in focal, unilateral epilepsy. A PowerPoint slide summarizing this article is available for download in the Supporting Information section here.

Effect of partial drug withdrawal on the lateralization of interictal epileptiform discharges and its relationship to surgical outcome in patients with hippocampal sclerosis

OBJECTIVE

To assess changes in the relative lateralization of interictal epileptiform discharges (IEDs) and interictal EEG prognostic value in terms of surgical outcome between periods with full medication (FMP) and reduced medication (RMP) in patients with temporal lobe epilepsy (TLE) associated with hippocampal sclerosis (HS).

METHODS

Interictal scalp EEGs of 43 patients were evaluated for the presence of IEDs separately in a waking state (WS) and sleeping state (SS) during FMP and RMP. In each period, patients were categorized as having unitemporal or bitemporal IEDs. Surgical outcome was classified at year 1 after surgery and at last follow-up visit as Engel I or Engel II-IV; and alternatively as completely seizure-free or not seizure-free.

RESULTS

There were significant changes in relative IED lateralization between FMP and RMP during SS. The representation of patients with unitemporal IEDs declined from 37 (86%) in FMP during SS to 25 (58%) in RMP during SS (p=0.003). At year 1 after surgery, the relative IED lateralization is a predictive factor for surgical outcome defined as Engel I vs. Engel II-IV in both FMP during WS (p=0.037) and during SS (p=0.007), and for surgical outcome defined as completely seizure-free vs. not seizure-free in FMP during SS (p=0.042). At last follow up visit, the relative IED lateralization is a predictor for outcome defined as Engel I vs. Engel II-IV in FMP during SS (p=0.020), and for outcome defined as completely seizure-free vs. not seizure-free in both FMP during WS (p=0.043) and in FMP during SS (p=0.015). When stepwise logistic regression analysis was applied, only FMP during SS was found to be an independent predictor for surgical outcome at year 1 after surgery (completely seizure-free vs. not seizure-free p=0.032, Engel I vs. Engel II-IV p=0.006) and at last follow-up visit (completely seizure-free vs. not seizure-free p=0.024, Engel I vs. Engel II-IV p=0.017). Gender was found to be independent predictor for surgical efficacy at year 1 if the outcome was defined as completely seizure-free vs. not seizure-free (p=0.036).

CONCLUSION

The predictive value of relative IED lateralization with respect to surgical outcome in interictal EEG is present only during FMP; the predictive value decreases with the reduction of AEDs caused by the change of relative IED lateralization.

Morphological variations of hippocampal formation in epilepsy: image, clinical and electrophysiological data

Morphological variations of hippocampal formation (MVHF) are observed in patients with epilepsy but also in asymptomatic individuals. The precise role of these findings in epilepsy is not yet fully understood. This study analyzes the hippocampal formation (HF) morphology of asymptomatic individuals (n = 30) and of patients with mesial temporal lobe epilepsy associated with hippocampal sclerosis (MTLE-HS) (n = 68), patients with malformations of cortical development (MCD) (n = 34), or patients with pure morphological variations of hippocampal formation (pure MVHF) (n = 12). Main clinical and electrophysiological data of patients with MVHF were also analyzed. Morphological variations of hippocampal formation are more frequently observed in patients with MCD than in patients with MTLE-HS or in asymptomatic individuals. Patients with pure morphological variations of hippocampal formation showed higher incidence of extratemporal seizure onset. Refractoriness seems to be more associated with other abnormalities, like HS or MCD, than with the HF variation itself. Thus, although morphological HF abnormalities might play a role in epileptogenicity, they seem to contribute less to refractoriness.

The mortality and morbidity of febrile seizures

Approaches to the treatment and investigation of febrile seizures have changed since the main reference studies on outcomes were conducted in the 1960s and 1970s. We have, therefore, conducted a systematic review of literature from the past 15 years to see whether outcomes have also changed. We found that simple febrile seizures do not carry a risk of death, but there is a very small risk of death after complex febrile seizures (CFSs), particularly febrile status epilepticus. There is no evidence that SUDEP (sudden unexpected death in epilepsy) occurs in association with febrile seizures. The risk of later epilepsy after a febrile seizure lies between 2.0% and 7.5%, and the risk of developing epilepsy after CFSs is estimated at around 10-20%. There is no evidence of any risk of hippocampal or mesial temporal sclerosis (HS/MTS) in association with simple febrile seizures. Serial imaging has shown that HS/MTS develops in 0-25% of patients over time after prolonged febrile seizures; the range in prevalence reflects selection bias in different studies. The overall risk of HS/MTS associated with CFSs is around 3%. Approximately 40% of patients with medically refractory temporal lobe epilepsy and HS/MTS on neuroimaging have a history of febrile seizures.

Correlation between temporal pole MRI abnormalities and surface ictal EEG patterns in patients with unilateral mesial temporal lobe epilepsy

OBJECTIVE

The objective of this retrospective study is to analyze ictal patterns observed during continuous Video-EEG monitoring in patients with temporal lobe epilepsy (TLE) due to unilateral hippocampal sclerosis (HS), and to correlate these EEG patterns to temporal pole abnormalities observed on magnetic resonance imaging exams.

METHODS

We analyzed 147 seizures from 35 patients with TLE and unilateral HS. Ictal patterns were classified and correlated to signal abnormalities and volumetric measures of the temporal poles. Volume differences over 10% were considered abnormal.

RESULTS

The most frequent type of ictal pattern was rhythmic theta activity (RTA), encountered in 65.5% of the seizures. Rhythmic beta activity (RBA) was observed in 11% of the seizures, localized attenuation in 8%, interruption of epileptiform discharges in 6%, repetitive discharges in 5.5%, and rhythmic delta activity (RDA) in 4%. Sixty-six percent of the patients presented signal abnormalities in the temporal pole that were always ipsilateral to the HS. Sixty percent presented significant asymmetry of the temporal poles consisting of reduced volume that was also always ipsilateral to HS. Although patients with RTA as the predominant ictal pattern tended to present asymmetry of temporal poles (p=0.305), the ictal EEG pattern did not correlate with temporal pole asymmetry or signal abnormalities.

CONCLUSIONS

RTA is the most frequent initial ictal pattern in patients with TLE due to unilateral HS. Temporal pole signal changes and volumetric reduction were commonly found in this group of patients, both abnormalities appearing always ipsilateral to the HS. However, neither temporal pole volume reduction nor signal abnormalities correlated with the predominant ictal pattern, suggesting that the temporal poles are not crucially involved in the process of epileptogenesis.

Epileptogenesis and chronic seizures in a mouse model of temporal lobe epilepsy are associated with distinct EEG patterns and selective neurochemical alterations in the contralateral hippocampus

Major aspects of temporal lobe epilepsy (TLE) can be reproduced in mice following a unilateral injection of kainic acid into the dorsal hippocampus. This treatment induces a non-convulsive status epilepticus and acute lesion of CA1, CA3c and hilar neurons, followed by a latent phase with ongoing ipsilateral neuronal degeneration. Spontaneous focal seizures mark the onset of the chronic phase. In striking contrast, the ventral hippocampus and the contralateral side remain structurally unaffected and seizure-free. In this study, functional and neurochemical alterations of the contralateral side were studied to find candidate mechanisms underlying the lack of a mirror focus in this model of TLE. A quantitative analysis of simultaneous, bilateral EEG recordings revealed a significant decrease of theta oscillations ipsilaterally during the latent phase and bilaterally during the chronic phase. Furthermore, the synchronization of bilateral activity, which is very high in control, was strongly reduced already during the latent phase and the decrease was independent of recurrent seizures. Immunohistochemical analysis performed in the contralateral hippocampus of kainate-treated mice revealed reduced calbindin-labeling of CA1 pyramidal cells; down-regulation of CCK-8 and up-regulation of NPY-labeling in mossy fibers; and a redistribution of galanin immunoreactivity. These changes collectively might limit neuronal excitability in CA1 and dentate gyrus, as well as glutamate release from mossy fiber terminals. Although these functional and neurochemical alterations might not be causally related, they likely reflect long-ranging network alterations underlying the independent evolution of the two hippocampal formations during the development of an epileptic focus in this model of TLE.

Failed surgery for temporal lobe epilepsy: Predictors of long-term seizure-free course

OBJECTIVES

To identify prognostic factors which predict the outcome 2 years after TLE surgery in those patients who were not seizure-free at the 6-month postoperative examination.

METHODS

We included 86 postoperative TLE patients who had undergone presurgical evaluation, including video-EEG and high-resolution MRI, and who had seizures between the second and sixth postoperative months.

RESULTS

32% of patients were seizure-free in the second postoperative year. We found that normal MRI findings and secondarily generalized seizures (SGTCS) preoperatively were associated with a non-seizure-free outcome, while rare postoperative seizures and ipsilateral temporal IED with seizure-free outcome. Newly administered levetiracetam showed a significant positive effect on the postoperative outcome independent of other prognostic factors. Five of seven patients who received levetiracetam became seizure-free (p = 0.006).

CONCLUSION

One-third of patients who did not become seizure-free immediately after surgery, eventually achieved long-term seizure freedom. We suggest watching for long-term seizure freedom after failed epilepsy surgery especially in patients who had rare postoperative seizures, focal MRI abnormality, ipsilateral temporal spikes, or no SGTCS preoperatively. Levetiracetam may have a positive effect on postsurgical seizures.

Vagus nerve stimulation: predictors of seizure freedom

OBJECTIVES

To identify predictive factors for the seizure-free outcome of vagus nerve stimulation (VNS).

METHODS

All 47 patients who had undergone VNS implantation at one centre and had at least one year of follow up were studied. They underwent complete presurgical evaluation including detailed clinical history, magnetic resonance imaging, and long term video-EEG with ictal and interictal recordings. After implantation, adjustment of stimulation parameters and concomitant antiepileptic drugs were at the discretion of the treating physician.

RESULTS

Mean (SD) age of the patients was 22.7 (11.6) years (range 7 to 53). Six patients (13%) became seizure-free after the VNS implantation. Only two variables showed a significant association with the seizure-free outcome: absence of bilateral interictal epileptiform discharges (IED) and presence of malformation of cortical development (MCD). Epilepsy duration showed a non-significant trend towards a negative association with outcome. By logistic regression analysis, only absence of bilateral IED correlated independently with successful VNS treatment (p<0.01, odds ratio = 29.2 (95% confidence interval, 2.4 to 353)). Bilateral IED (independent or bilateral synchronous) was found in one of six seizure-free patients and in 33 of 41 non-seizure-free patients. When bilateral IED were absent, the sensitivity for seizure-free outcome was 0.83 (0.44 to 0.97), and the specificity was 0.80 (0.66 to 0.90).

CONCLUSIONS

Bilateral IED was independently associated with the outcome of VNS. These results are preliminary because they were based on a small patient population. They may facilitate prospective VNS studies enrolling larger numbers of patients to confirm the results.