Background: Vagal nerve stimulation is a new non-pharmacological therapy for patients with refractory epilepsy. Introduced in USA in 1988, the treatment is based on animal experiments demonstrating that intermittent stimulation of the vagal nerve could prevent or reduce the frequency and/or duration of seizures.
Material and methods: At the National Hospital in Norway, 47 therapy-resistant patients have had a vagal nerve stimulator implanted since June 1993. We have used the Neuro-Cybernetic Prosthesis system from Cyberonics, consisting of a programmable pulse generator, a bipolar vagal nerve stimulator lead, a programming wand with accompanying software, and a hand-held magnet. The mean age of the population was 34.4 years (12-70 years). All had a long-standing epilepsy with frequent seizures, 36 (77%) had seizures every day. The majority (89%) had localization-related epilepsy. Mean follow-up time was 2.7 years (0.4-6.5 years).
Results: 16 patients (34%) responded to the treatment with > 50% reduction in seizure frequency. No one, however, became seizure free. 20 patients (43%) had no seizure reduction. 24 of the patients (51%) benefited from extra stimulation triggered by the magnet. The stimulation affected several types of seizures; most often a reduction in frequency of secondary generalised tonic-clonic seizures was noted. Hoarseness, coughing and a tingling sensation in the throat were the most frequently reported side effects occurring during stimulation. The patients tended to habituate to these side effects. In 14 patients (30%), the device has been explanted, mostly due to lack of efficacy.
Interpretation: Considering the fact that this patient group belongs to the most refractory part of the epilepsy population, the results are regarded as promising and they are in keeping with results from other studies. However, the role of vagal nerve stimulation in the future treatment of epilepsy is still not settled. Several questions remain unanswered, e.g. what are the exact mechanisms of action behind the seizure reducing effect, and which patients are most suitable for this treatment?