[Vagus nerve stimulation (VNS) in the treatment of drug-resistant epilepsy. A 4-year follow-up evaluation of VNS treatment efficacy]

Abstract

Objectives: Vagus nerve stimulation (VNS) is an alternative non-destructive surgical treatment for patients with medically intractable epilepsy. Neither the rationale nor proper indications for this treatment modality have been fully established yet.

Aim of the study: To assess the long-term efficacy of chronic VNS.

Material: A series of 6 patients with drug-resistant epilepsy, subjected to VNS therapy. (4 females, 2 males, mean age 35.5 years, 3 patients with focal epilepsy, 3 with non-focal epilepsy, mean history of seizures 10 years, seizures frequency 10-400/per month).

Method: An open-label prospective study with a 4-year follow-up.

Results: At a 4-year follow-up one patient (with non-focal epilepsy) was seizure-free, with only rare episodes of aura (Engel Ia), while in another one (with bitemporal epilepsy) seizures frequency remained unchanged with VNS (Engel IVb). In the remaining 4 cases (one with bitemporal, one with parietal, and two with non-focal epilepsy) the mean overall reduction in seizures frequency as compared to the baseline was 60% (Engel IIIa). VNS resulted in a reduction of seizures by 90% in a patient with a history of an unsuccessful anterior callosotomy.

Conclusions: 1. VNS was found to reduce both the frequency of seizures (an overall 60% reduction in seizures frequency) and the duration of post-seizure consciousness disturbances in focal and non-focal epilepsies, but seizures-free state could be obtained in only one out of six patients. 2. A previous unsuccessful callosotomy did not prevent a good anticonvulsant effect in one patient. 3. The anticonvulsant effect of VNS was cumulative over time during the first 3 years postoperatively, then it tended to reach a plateau. 4. The best clinical outcome was positively correlated with the currents 1.5-2.0 mA. No significant correlation was noted for the current adjustments at the level of 2.0-3.5 mA. 5. Since no difference between the two stimulation patterns tested (30 s stimulation + 5 min break vs. 14 s + 3 min) was found as regards the anticonvulsant action of VNS, the latter pattern was subsequently used as the one more sparing the battery.