Surgery and Electrical Stimulation in Epilepsy: Selection of Candidates and Results

Up to What Extent Does Dravet Syndrome Benefit From Neurostimulation Techniques?

Background

Dravet syndrome (DS) is a refractory developmental and epileptic encephalopathy (EE) with a variety of comorbidities, including cognitive impairment, autism-like behavior, speech dysfunction, and ataxia, which can seriously affect the quality of life of patients and impose a great burden on society and their families. Currently, the pharmacological therapy is patient dependent and may work or not. Neuromodulation techniques, including vagus nerve stimulation (VNS), deep brain stimulation (DBS), transcranial magnetic stimulation (TMS), responsive neurostimulation (RNS), and chronic subthreshold cortical stimulation (CSCS), have become common adjuvant therapies for neurological diseases, but their efficacy in the treatment of DS is unknown.

Methods

We searched Web of Science, PubMed, and SpringerLink for all published cases related to the neuromodulation techniques of DS until January 15, 2022. The systematic review was supplemented with relevant articles from the references. The results reported by each study were summarized narratively.

Results

The Web of science, PubMed and SpringerLink search yielded 258 items. A total of 16 studies published between 2016 and 2021 met the final inclusion criteria. Overall, 16 articles (109 cases) were included in this study, among which fifteen (107 patients) were involved VNS, and one (2 patients) was involved DBS. After VNS implantation, seizures were reduced to ≥50% in 60 cases (56%), seizure free were found in 8 cases (7.5%). Only two DS patients received DBS treatment, and the initial outcomes of DBS implantation were unsatisfactory. The seizures significantly improved over time for both DBS patients after the addition of antiepileptic drugs.

Conclusion

More than half of the DS patients benefited from VNS, and VNS may be effective in the treatment of DS. However, it is important to note that VNS does not guarantee improvement of seizures, and there is a risk of infection and subsequent device failure. Although DBS is a safe and effective strategy for the treatment of refractory epilepsy, the role of DBS in DS needs further study, as the sample size was small. Thus far, there is no strong evidence for the role of DBS in DS.

Combination of corpus callosotomy and vagus nerve stimulation in the treatment of refractory epilepsy

BACKGROUND

Palliative techniques such as partial corpus callosotomy (CC) and vagus nerve stimulation (VNS) may be effective for adequate control of seizures in pharmacoresistant patients who are not candidates for resective surgery.

OBJECTIVE

The objective of this study was to analyze the efficacy of the combination of these two techniques in patients where the first surgery had not achieved adequate control.

MATERIALS AND METHODS

This is a retrospective review of 6 patients with refractory epilepsy in which both types of surgery were performed, CC and VNS. We analyzed variables such as age, sex, age at onset of epilepsy, seizure types, electroencephalogram and magnetic resonance imaging results, and number of pre- and postoperative seizures.

RESULTS

Three patients first underwent VNS and then CC, and 3 patients were treated in reverse order. All patients had some improvement after the first surgery, but they continued to experience persistent falls, so a second palliative technique was used. The mean improvement after both surgeries was 89% (90% in patients first receiving CC and 87% in patients who first underwent VNS).

CONCLUSIONS

In adequately studied patients who are not optimal candidates for resective surgery, palliative surgery is a choice. The combination of VNS and CC shows good results in our series, although the right order to perform both procedures has not been defined. These results should be confirmed in a larger group of patients.

Validation of FDG-PET/MRI coregistration in nonlesional refractory childhood epilepsy

PURPOSE

To validate the use of 18F-fluorodeoxyglucose-positron emission tomography/magnetic resonance imaging (FDG-PET/MRI) coregistration for epileptogenic zone detection in children with MRI nonlesional refractory epilepsy and to assess its ability to guide a second interpretation of the MRI studies.

METHODS

Thirty-one children with refractory epilepsy whose MRI results were nonlesional were included prospectively. All patients underwent presurgical evaluation following the standard protocol of our epilepsy unit, which included FDG-PET and FDG-PET/MRI coregistration. Cerebral areas of decreased uptake in PET and PET/MRI fusion images were compared visually and then contrasted with presumed epileptogenic zone localization, which had been obtained from other clinical data. A second interpretation of MRI studies was carried out, focusing on the exact anatomic region in which hypometabolism was located in FDG-PET/MRI fusion images.

KEY FINDINGS

Both FDG-PET and FDG-PET/MRI detected hypometabolism in 67.8% of patients, with good concordance on a subject basis and on the cerebral region involved (κ statistic = 0.83 and 0.79, respectively). Hypometabolism detected by single PET, as well as by PET/MRI fusion images, was located in the same hemisphere, as indicated by electroclinical data in 58% of patients, and at the same place in 39% of cases. Of the patients who showed hypometabolism on PET/MRI, 43% also experienced changes in the guided second MRI interpretation, from nonlesional to subtle-lesional.

SIGNIFICANCE

PET/MRI coregistration is an imaging variant that is at least as accurate as PET alone in detecting epileptogenic zone in pediatric nonlesional patients, and can guide a second look at MRI studies previously reported as nonlesional, turning a meaningful percentage into subtle-lesional.

Long-term effect of vagus nerve stimulation on interictal epileptiform discharges in refractory epilepsy

BACKGROUND

Vagus nerve stimulation (VNS) therapy has been widely recognized as an effective alternative for the treatment of refractory epilepsy. However, the precise mechanism of VNS is poorly understood. The purpose of this study was to observe the long-term interictal EEG changes induced by VNS, and to investigate the probable mechanism of action of VNS in achieving seizure control.

METHODS

Eight patients with VNS were selected from two epilepsy centers in China (Harbin and Shanghai) between 2001 and 2004. We studied the clinical efficacy by long-term follow-up, ranging from 37 to 81 months (mean 55.8 months). Moreover, serial EEGs were performed at the different time (preoperative baseline, 3, 6, 12, and 24 months after VNS initiation) and the different states of VNS stimulator ("activation", "deactivation" and "reactivation").

RESULTS

A > or = 50% seizure reduction was achieved in 12.5%, 62.5%, 75%, 62.5% and 75% of the total patients (n=8) at 6, 12, 18, 24 and 36 months of post-VNS, respectively. The results revealed a statistically significant progressive decrease in the number of IEDs (interictal epileptiform discharges) on EEG with time (P<0.01). Significant correlation had been highlighted after 6 months of VNS stimulation, between the reduction of seizure frequency and the decreasing of IEDs (P<0.01). Furthermore, statistically significant difference of IEDs was seen when comparing the state of "deactivation" with the states of "activation" and "reactivation", respectively (P<0.01). However, there was no significant difference in IEDs between "activation" and "reactivation" (P>0.05).

CONCLUSIONS

VNS is an efficient, well-tolerated therapy for refractory epilepsy. It can induce progressive electrophysiological effect on epileptiform activity over time. This may reflect the mechanism of chronic action of VNS with desynchronization of EEG in achieving seizure control.