Abstracts

Patients with refractory epilepsy who require the use of the Vagus Nerve Stimulator (VNS) commonly have side effects. Strategies limiting adverse reactions induced by the VNS may improve the patient[apos]s quality of life.
Medical records of 80 patients with VNS implantation were reviewed from 8/1/1998 until the present. Device diagnostic testing, including lead impedance check was performed during VNS placement in the operating room. However, VNS was not turned on until the first clinic visit. All patients were followed by the members of the Epilepsy Clinic at the Children[apos]s Hospital and Regional Medical Center. Stimulation parameters were adjusted for efficacy. Duty cycles ranged from 10-45%. Current was increased to up the limit of tolerance or to 2 miliamperes (maximal range 1-2 miliamperes).
Twelve of the 80 (15%) patients had significant side-effects. Minor degrees of discomfort and voice alteration with the on-time were not included in these 12 cases (see below). Voice changes during the on-time tend to be persistent and virtually universal but disappear when patients hold the magnet over the VNS turning it off when they have to speak in public. Three patients (2 positive history of asthma) had wheezing during the on-time that disappeared with shortening of pulse width from 500 to 250 miliseconds. Two patients had a vocal cord paralysis (one had also swallowing dysfunction) after the VNS implantation, presenting with hypophonic voice after the surgery but before the VNS was turned on. Voice and swallowing abnormalities resolved after turning on the VNS, raising the possibility that the electrical stimulation may actually expedite the recovery when the lesion is neurapraxis due to nerve manipulation. Four patients had a wound infection. Severe cognitive dysfunction with obsessive traits (3) leading to picking on the scar probably contributed to wound infection. Explantation of the VNS was done in all four cases after a short course of antibiotic therapy. [quot][italic]De novo[/italic][quot] high lead impedance on a previously normal functioning VNS was seen in five cases due to spontaneous lead fractures (3), poor lead contact (1) or unknown (1). Moderate pain/discomfort was reported or inferred in about 30%. This may be an underestimate due to difficulties related to age or mental status. Discomfort was assumed when during the on-time the patients had significant cough with color changes and touching of the neck. Subjective/inferred discomfort tended to improve or disappear immediately with shortening of the pulse width from 500 to 250 microseconds.
VNS is a therapy for epilepsy of difficult control that is associated with side-effects. Most adverse reactions are manageable. Turning on the VNS may help expedite post-operative recurrent nerve dysfunction. High lead impedance in a previously normal functioning VNS is suggestive of a lead fracture.