Abstract
Vagal nerve stimulation (VNS) is a safe alternative therapy for epilepsy but may have rare significant complications. There is no consensus regarding the necessity of video-EEG monitoring to characterize events before the VNS implantation. The authors discuss four patients who were inappropriately referred for or implanted with VNS without any previous video-EEG monitoring, in the context of their entire case experience.
Vagus nerve stimulation (VNS) has emerged as an effective adjunctive therapy for medically refractory epilepsy with a median reduction in seizures from 34 to 45% at 1 year and a >75% reduction in seizures in 20% of patients.1 VNS provides a programmed, regular stimulus from a chest-implanted generator via coiled electrodes tunneled to the left cervical vagus nerve.2 Although VNS is generally safe, there are a number of rare but serious complications associated with it, including deterioration of figural memory,3 Horner’s syndrome,4 lowering of pain threshold,5 adverse changes in respiration during sleep,6 bradycardia and asystole during intraoperative testing of the device,7 vocal cord paralysis, neck pain, and aspiration.8 Surgery can be done with a regional cervical block, but most often it is done during general anesthesia. In addition to potential morbidity and mortality associated with exposure to general anesthesia, stimulating electrodes can injure nerves by mechanical trauma, electrodeposition of toxic materials, or “excitotoxic” overstimulation.9 There is no consensus regarding the necessity of video-EEG monitoring to characterize events before the implantation of a VNS.
Results.
Since the VNS became available, we have cared for 27 patients who either had a VNS when they were referred to us or had it implanted by us or were referred directly to our neurosurgeons for implantation. Sixteen of the 27 patients had VNS implanted by us after they had been evaluated with brain MRIs that use special sequences to identify mesial temporal sclerosis and with video-EEG to characterize and electrographically localize their events. All of these patients were diagnosed with epilepsy and were not candidates for a surgical procedure with a cure rate higher than the VNS.
Of the other 11 patients, 7 were sent to us with VNS already implanted, and none of them had had a full presurgical workup. Four (these are the patients described below) were referred directly to our neurosurgeon for implantation. Two had only nonepileptic behavioral events. Another had a grade 2 astrocytoma that was causing the seizures. A fourth had left mesial temporal sclerosis and left mesial temporal seizures. He underwent a selective left amygdalohippocampectomy and has been seizure free. His chances for seizure freedom were minimal had he had the VNS implanted.
Patient 1.
Patient 1 was a 30-year-old right-handed woman with history of two types of “seizures” since a closed head injury at age 14 years. She had failed to respond to six antiseizure medications. She also had a VNS implanted a few months earlier. The first seizure type was characterized by loss of consciousness, left side shaking for 1 to 2 minutes, without any confusion afterward. These occurred 3 to 10 times a day. The second type, referred to as “grand mal,” was characterized by generalized shaking that lasted for 4 to 5 minutes. She had these three times a week. She was admitted for video-EEG monitoring during which we captured several of her smaller events and two of her larger ones. During one of the larger events, she reached for the magnet lying on the bedside table even though she was unresponsive to verbal stimuli and had generalized shaking. The EEG was normal with normal awake background during both types of events, and no epileptiform abnormalities were present. She was diagnosed with nonepileptic behavioral events after family confirmed that her typical events had been recorded.
Patient 2.
Patient 2 was a 38-year-old right-handed man with unusual events. He described the events as repetitive electric sensations in the neck that radiated to the chest, associated with blurred vision and loud noises for several minutes, and occurring in clusters of several per day. He had occasional loss of awareness with most of these, but there was no shaking, oral trauma, or incontinence. After several trials of antiseizure medications failed to improve these events, he was considered for VNS. He was admitted for video-EEG monitoring. During the 24 hours he was monitored, he had multiple typical events. He was unresponsive during them and for a short while afterward. The EEG showed normal awake background, marred by some movement artifact, but no epileptiform abnormalities were present. He was diagnosed with nonepileptic behavioral events.
Patient 3.
A 44-year-old right-handed man was referred for VNS implantation because of a 7-year history of “complex partial seizures” refractory to medication. His history was significant for febrile seizures as an infant. His events were characterized by a rising epigastric sensation followed by behavioral arrest, staring, decreased responsiveness, and oral and gestural automatisms. These occurred approximately three to eight times per month. He had failed to respond to four antiseizure medications. Because of the clinical semiology of his seizures, he was admitted for workup. An MRI of the brain revealed left mesial temporal sclerosis; a PET scan showed left temporal hypometabolism; the interictal EEG had left anterior temporal discharges; and all seizures that were captured on video-EEG originated from the anterior left temporal electrodes. He underwent selective left amygdalohippocampectomy and had been seizure free for 1 year at his most recent follow-up visit approximately 1 month ago.
Patient 4.
Patient 4 was a 20-year-old right-handed woman with multiple seizure types since age 7 years. She had had a brain CT and video-EEG monitoring in the mid-1980s. The parents were told that there was a possible lesion on the CT scan. The EEG report mentioned right temporal sharp waves. She remained intractable to multiple medications and continued to have falls with secondary injuries. Two years earlier, she had a VNS implanted without obtaining an MRI of brain. The family reported that the VNS reduced the frequency but did not completely stop the generalized seizures. Patient 4 was admitted for video-EEG monitoring, and her seizures were localized to the right mid-temporal electrodes. A PET scan revealed decreased metabolism in the right temporal lobe. Her MRI revealed a cystic lesion in the right temporal lobe. The lesion was resected, and the pathology was consistent with a grade 2 mixed oligoastrocytoma. Her seizures have been reduced by more than 50%.
Discussion.
Implanting the VNS is a well-tolerated procedure with low morbidity; nevertheless, it is an invasive procedure with some risks involved. Its efficacy in patients with intractable epilepsy is reasonable, but it does not constitute a cure and does not control all seizures. Temporal lobe surgery for intractable unilateral mesial temporal lobe seizures is effective in completely controlling the seizures in 58 to 64% of patients with a low morbidity and mortality.10
Four of the 11 patients referred to us from an outside hospital without inpatient evaluation were not ideal candidates for VNS. The 16 patients evaluated at our institution were ideal candidates for VNS because all had epileptic seizures and none were candidates for any of the surgical procedures mentioned previously. That is a significant difference, according to the Fisher’s exact test, with a p value of 0.0188 at a 95% CI.
We realize that our study is limited because of our small sample and is inadequate to definitely conclude that video-EEG before VNS implantation is required. However, it raises an important question that needs a larger, prospective study with comparative analysis of risk to answer.
- Received November 21, 2002.
- Accepted in final form March 28, 2003.
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