Efficacy of Neuromodulation Therapy with Vagus Nerve Stimulator in Patients with Drug-Resistant Epilepsy on Unchanged Antiepileptic Medication Regimen for 24 Months Following the Implant

To establish efficacy of vagus nerve stimulation (VNS) therapy in the treatment of intractable epilepsy, we compared outcome data from the baseline period to the maintenance period (7 to 24 months post-implant) by calculating the mean seizure frequency at 6-month intervals (7 to 12 months - first study period, 13 to 18 months - second study period, and 19 to 24 months - third study period), in 39 consecutive patients on unchanged antiepilepsy drug (AED) regimen for 24 months following the VNS implant. Of the 39 patients24 (61.5%) at first study period, 25 (64.1 %) at second study period and 25 (64.1 %) at third study period were responders (≥50% reduction in seizures). Twenty one (53.9 %) patients were responders in all three study periods. Incremental seizure control was seen in 15 of these 21 patients. Although 3 (7.7%), 4 (10.3 %) and 8 (20.5%) patients had a total (100%) seizure control at first, second and third study periods respectively, no patient remained seizure-free through all 3 study periods. Seven (17.9%) patients were partial responders (≥ 50% seizure reduction in two or less study periods). Eleven patients (28.2%) were non-responders (< 50% seizure reduction in all 3 study periods). Twenty three patients (59%) had partial epilepsy with and without secondarily generalization and 16 patients (41%) had primary generalized epilepsy. Eleven (47.8%) of the 23 patients with partial epilepsy and 10 (62.5%) of the 16 patients with generalized epilepsy were responders in all three study periods. We conclude that: 1) More than 60 % of patients on unchanged AED regimen continued to be responders at 24 months following the VNS implant. 2) A trend towards increasing responder rate with increasing duration of VNS therapy was observed.3) No major complications or side effects requiring discontinuation of VNS therapy were noted.