M. D'Havé

Programmed and magnet-induced vagus nerve stimulation for refractory epilepsy

Summary Vagus nerve stimulation (VNS) is an effective alternative treatment for patients with refractory epilepsy. The generator produces intermittent stimulation trains and does not require patient intervention. Using currently available technology, continuous stimulation is incompatible with a reasonable battery life. Because earlier studies have demonstrated the persistence of a stimulation effect after discontinuation of the stimulation train, we intended to evaluate the clinical efficacy of VNS in both the programmed intermittent stimulation mode and the magnet stimulation mode. Patients, companions, and caregivers were instructed on how to administer additional stimulation trains when an aura or a seizure onset occurred. We assumed that patients or caregivers could recognize habitual seizures and were able to evaluate sudden interruption of these seizures. During a mean follow-up of 35 months, 46% of patients became responders, with a reduction in seizure frequency of more than 50%. Twenty-nine percent of patients stopped having convulsive seizures. In two thirds of patients who were able to self-administer or receive additional magnet stimulation, seizures could be interrupted consistently or occasionally. More than half of the patients who reported a positive effect of magnet stimulation became responders. Only three patients were able to use the magnet themselves. In most cases, support from caregivers was necessary. This study is the first to document the efficacy of magnet-induced VNS in a larger patient population during long-term follow-up. The magnet is a useful tool that provides patients who are treated with VNS and mainly caregivers of such patients with an additional means of controlling seizures. To further confirm the self-reported results from our patients, additional studies comparing programmed stimulation and magnet-induced stimulation during monitoring conditions are needed.

Acute single photon emission computed tomographic study of vagus nerve stimulation in refractory epilepsy

Summary: Purpose: Left‐sided vagus nerve stimulation (VNS) is an efficacious treatment for patients with refractory epilepsy. The precise mechanism of action remains to be elucidated. Only limited data on VNS‐induced changes in regional cerebral blood flow (rCBF) are available. The aim of this study was to investigate rCBF changes during initial VNS with single‐photon emission computed tomography (SPECT).

Direct Medical Costs of Refractory Epilepsy Incurred by Three Different Treatment Modalities: A Prospective Assessment

Summary:  Purpose: More than 20% of epilepsy patients have refractory seizures. Treatment options for these patients include continued polytherapy with/without novel antiepileptic drugs (AEDs), epilepsy surgery (ES), or vagus nerve stimulation (VNS). The purpose of this study was prospectively to compare epilepsy‐related direct medical costs (ERDMCs) incurred by these different treatment modalities.

Dipole Modeling in Epilepsy Surgery Candidates

Summary: Purpose: The validity and clinical significance of dipole modeling in epilepsy surgery candidates is not fully established.

Dipole location errors in electroencephalogram source analysis due to volume conductor model errors

An examination is made of dipole location errors in electroencephalogram (EEG) source analysis, due to not incorporating the ventricular system (VS), omitting a hole in the skull and underestimating skull conductivity. The simulations are performed for a large number of test dipoles in 3D using the finite difference method. The maximum dipole location error encountered, utilising 27 and 53 electrodes is 7.6 mm and 6.1 mm, respectively when omitting the VS, 5.6 mm and 5.2 mm, respectively when neglecting the hole in the skull, and 33.4 mm and 28.0 mm, respectively when underestimating skull conductivity. The largest location errors due to neglecting the VS can be found in the vicinity of the VS. The largest location erros due to omitting a hole can be found in the vicinity of the hole. At these positions the fitted dipoles are found close to the hole. When skull conductivity is underestimated, the dipole is fitted close to the skull-brain border in a radial direction for all test dipoles. It was found that the location errors due to underestimating skull conductivity are typically higher than those found due to neglecting the VS or neglecting a hole in the skull.

VAGUS NERVE STIMULATION FOR MEDICALLY REFRACTORY EPILEPSY; EFFICACY AND COST-BENEFIT ANALYSIS

Summary Introduction. Vagus nerve stimulation is a novel treatment for patients with medically refractory epilepsy, who are not candidates for conventional epilepsy surgery, or who have had such surgery without optimal outcome. To date only studies with relatively short follow-up are available. In these studies efficacy increased with time and reached a maximum after a period of 6 to 12 months. Implantation of a vagus nerve stimulator requires an important financial investment but a cost-benefit analysis has not been published. Patients and Methods. Our own experience with VNS in Gent comprises 15 patients with mean age of 29 years (range: 17–44 years) and mean duration of epilepsy of 18 years (range: 4–32 years). All patients underwent a comprehensive presurgical evaluation and were found not to be suitable candidates for resective epilepsy surgery. Mean post-implantation follow-up is 24 months (range: 7–43 months). In patients with follow-up of at least one year, efficacy of treatment in terms of seizure control and seizure severity was assessed one year before and after the implantation of a vagus nerve stimulator. Epilepsy-related direct medical costs (ERDMC) before and after the implantation were also compared. Results. A mean reduction of seizure frequency from 14 seizures/month (range: 2–40/month) to 8 seizures/month (range: 0–30/month) was achieved (Wilcoxon signed rank test n=14; p=0.0016). Five patients showed a marked seizure reduction of ≥50%; 6 became free of complex partial seizures, 3 of whom became entirely seizure free for more than 12 months; 2 patients had a worthwhile reduction of seizure frequency between 30–50%; in 2 patients seizure frequency reduction has remained practically unchanged. Seizure freedom or ≥50% seizure reduction was achieved within the first 4 months after implantation in 6/11 patients. Before the implantation, the mean yearly epilepsy-related direct medical costs per patient were estimated to be 8830US

Interictal and ictal dipole modelling in patients with refractory partial epilepsy

(n=13; range: 1879–31129US

The Validation of the Finite Difference Method and Reciprocity for Solving the Inverse Problem in EEG Dipole Source Analysis

; sd=7667); the average number of hospital admission days per year was 21 (range: 4–100; sd=25.7). In the 12 months after implantation, ERDMC had decreased to 4215US

Ictal Source localization in presurgical patients with refractory epilepsy

(range: 615–11794US

Influence of measurement noise and electrode mislocalisation on EEG dipole-source localisation

; sd=3558) (Wilcoxon signed rank test n=13; p=0.018) and the average number of admission days to 8 (range: 0–35) (Wilcoxon signed rank test n=13; p=0.023). Conclusion. VNS is an effective treatment of refractory epilepsy and remains effective during long-term follow-up. Cost-benefit analysis suggests that the cost of VNS is saved within two years following implantation.