Two important studies of VNS (Ben-Menachem 1994, Handforth 1998) both found a significant reduction in seizure frequency. These were double-blind studies conducted at several medical centers. Each of the patients studied had a VNS implant, but some had only low-level stimulation. These studies showed that patients receiving high-level stimulation had a mean decrease in frequency of seizures of about 25% after 3 months. About one-third of the patients actively treated with VNS experienced a reduction in seizure frequency of at least 50%. In addition, a 1994 long-term study (George 1994) showed a cumulative improvement in efficacy at 1 year.

In 2000, a large prospective study of VNS (DeGiorgio 2000) was reported. This study involved 195 patients over a 15-month period at 20 medical centers. It consisted of an initial 3-month randomized, double-blind phase, during which patients received either low stimulation or high stimulation, followed by a 12-month period in which all patients received high-level stimulation. The median reduction in seizures at 3 months, after completion of the initial double-blind study, was 34%. At 12 months, the reduction in seizure frequency was 45%. Furthermore, at 12 months, 35% of the 195 subjects had a greater than 50% reduction in seizures and 20% had a reduction greater than 75%. At 3 months, only 11% of the subjects had experienced a reduction in seizures of more than 75%, so the investigators concluded that the efficacy of VNS improves during 12 months.

The latest findings

New research on VNS was a major focus at annual meeting of the American Epilepsy Society in December, 2000. At a symposium on neurostimulation, it was reported that long-term efficacy studies lasting up to 5 years show that VNS can help a wide array of epilepsy patients who do not respond to seizure medicines and cannot be treated with epilepsy surgery. Overall, the studies indicated that 34% to 48% of these adult patients (usually with partial seizures with or without secondary generalization) experienced at least a 50% reduction in seizure frequency after 2 to 5 years of follow-up.

Researchers also reported finding that during VNS, blood flow increases in the brain stem, thalamus, frontal lobe, hippocampal areas, and cerebellum—areas that play an important role in seizure activity.

Mood and anxiety also tend to improve in patients treated with VNS, according to research presented at the meeting. Other presentations showed that VNS seems to be effective in a broad range of seizure types in children.

In conclusion, data now indicate that VNS is a promising treatment option for a broad spectrum of epilepsy patients who are refractory to medications (failure of two or three antiepileptic drugs) and cannot be helped by epilepsy surgery.

References

Find the original articles at www.ncbi.nlm.nih.gov/pubmed

Ben-Menachem E, et al. Vagus nerve stimulation for treatment of partial seizures: A controlled study of effect on seizures. First International Vagus Nerve Stimulation Study Group. Epilepsia. 1994 May-Jun;35(3):616-26. [PMID: 8026408]

Handforth A, et al. Vagus nerve stimulation therapy for partial-onset seizures: a randomized active-control trial. Neurology 1998 Jul;51(1):48-55. [PMID: 9674777]

George R, et al. Vagus nerve stimulation for treatment of partial seizures: 3. Long-term follow-up on first 67 patients exiting a controlled study. First International Vagus Nerv Stimulation Study Group. Epilepsia. 1994 May-Jun;35(3):637-43. [PMID: 8026410]

DeGiorgio CM, et al. Prospective long-term study of vagus nerve stimulation for the treatment of refractory seizures. Epilepsia 2000 Sep;41(9):1195-200. [PMID: 10999559]

Topic Editor: Steven C. Schachter, M.D.
Last Reviewed:11/5/03