Adverse events occur in 35% of VNS patients.
PITTSBURGH -- Treatment-limiting adverse events occurred in more than 30% of patients who received a vagus nerve stimulator for the treatment of seizure disorders, Dr. Phillip Pearl reported at the annual meeting of the Child Neurology Society.
The number of adverse events may in-crease even more as vagus nerve stimulator (VNS) devices become more common among new populations of patients with seizure disorders, said Dr. Pearl. "I think this is probably the tip of the iceberg and that we will be seeing more cases as more people receive this device and as the longevity of VNS therapy increases beyond what was studied for the initial approval."
Dr. Pearl reported adverse events among 62 patients who had VNS devices implanted in 1998-2005 at the Children's National Medical Center, Washington, where he is a pediatric neurologist. The patients ranged in age from 3 to 29 years (median 12 years). The median duration of therapy was 40 months (range 1-96 months).
Of the 62 patients, 35% (22 patients) had at least one clinically significant adverse event. The most common were persistent drooling (six), coughing (five), throat discomfort or spasms (four), and dysphagia (three). Two patients had difficulty breathing, with one requiring device removal. Two experienced vomiting while the VNS current was delivered, and two more experienced vocal cord weakness. All of these adverse events required some limiting of the current output of the device. Two more patients experienced axillary wound infections that required oral antibiotic treatment.
Of the patients with adverse events, eight needed nonroutine surgical intervention. The device was removed from five patients (8%), including a 13-year-old girl who developed serious complications from a wound infection requiring intravenous antibiotics. She also needed a percutaneous endoscopic gastronomy tube because of vocal cord paralysis and persistent dysphagia. The other four explantations were necessary because of persistent problems with breathing, coughing, or throat discomfort.
There were also two lead failures, Dr. Pearl said. One was discovered during a routine device interrogation more than 7 years after the initial implant. The other one was discovered after seizure control worsened.
In addition to these adverse events, there were two patients who experienced unique unanticipated problems.
One was a 13-year-old boy who had received the implant for intractable generalized seizures and was seen at an emergency department for convulsive status.
Peripheral vein access was limited; an emergency physician searching for an access site misidentified the VNS wire in the boy's neck as the jugular vein.
"The wire was stabbed several times until it became apparent that it was not a vein," Dr. Pearl said. Interrogation of the device a few days later showed no evidence of malfunction. One year later, the device did malfunction; the patient experienced increased seizures and needed a replacement.
Finally, Dr. Pearl said, a 25-year-old man with a VNS for intractable absence seizures began to experience tingling in the left side of his neck about 3 months after implantation. There was no indication that the device was malfunctioning, but the tingling did not occur when it was turned off. Subsequent x-rays showed that there was no strain-relief loop in the VNS wire located over the sternocleidomastoid muscle. Rather than have a revision, the patient continues to tolerate the intermittent sensations, Dr. Pearl said.
BY MICHELE G. SULLIVAN