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

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.