- Jeanne Lenzer, medical investigative journalist1,
- Shannon Brownlee, instructor, Dartmouth Institute for Health Policy and Clinical Practice2
- 1New York
- 2Washington, DC
In 1997, the US Food and Drug Administration’s neurological devices panel met to consider approval of a vagus nerve stimulator (VNS). The manufacturer, Cyberonics, said it could prevent or reduce seizures in patients with partial onset epilepsy who did not respond to drug treatment. The device consists of a generator the size of a matchbox that is implanted under the skin below the patient’s clavicle. Lead wires from the generator are tunnelled up to the patient’s neck and wrapped around the left vagus nerve at the carotid sheath, where it delivers electrical impulses to the nerve lasting about 30 seconds every 3-5 minutes.
Representatives from Cyberonics offered no definitive explanation during the FDA meeting of how the device stopped or reduced seizures, but they had three studies, E03, E04, and E05, to show its safety and efficacy.
Two of the studies, E03 and E05, involved 313 patients with treatment resistant partial seizures randomised to high or low dose stimulation. The low stimulation arm was intended to avoid the problem of an unblinded placebo arm because all patients would be implanted and told they were receiving stimulation. The studies did not include a medical treatment arm for comparison, leaving unanswered the question of whether either treatment arm was superior to existing care.
Researchers reported that 25% of patients in the high stimulation arms of the trials achieved the primary end point: a 50% reduction in seizure frequency from baseline. However, 20% of patients in the high stimulation arm had more seizures.1
Concerns about safety
The safety of the device hinged on the cause of death …