Vagus nerve stimulation (VNS)—a novel therapy for partial and generalized epilepsy—involves the repetitive stimulation of the left vagus nerve via connections from a programmable neurocybernetic prosthesis implanted in the left upper chest region.131 Intermittent stimulation of the vagus nerve may be supplemented by additional activation of the device at the onset of a seizure by holding a magnet over the left chest wall region.
VNS is a generally well-tolerated treatment. Adverse events include hoarseness, tingling sensations in the neck, or intermittent voice alterations, all of which usually abate significantly over time.
Although VNS therapy is more invasive than the administration of antiepileptic drugs (AEDs), it has a number of advantages over typical AED treatment, especially an absence of central nervous system side effects such as sedation and impairment of cognition.
Although VNS has been studied more extensively in the epilepsy patients with partial seizures and no developmental disabilities (DD), it is a welcome addition to the therapeutic armamentarium against refractory generalized epilepsy syndromes common to the DD population, such as Lennox-Gastaut syndrome.133 Preliminary reports of VNS experience in this population have been impressive, reporting reductions in seizures and increased attention and alertness.134 In one report of 15 children with the Lennox-Gastaut syndrome or myoclonic epilepsies of infancy,135 more than 25% of patients had seizure reduction greater than 50%. The methods for supporting the claim that behavioral improvements occurred independent of seizure reduction were not clarified.
Many clinicians may be concerned about implanting devices in DD patients, fearing that patients will pull at the operative site in the chest wall. Recent experience with VNS has defied these concerns, with good tolerance of the implant. Nevertheless, such patients should be watched carefully in the immediate postoperative period (Paul Devereaux, Cyberonics Corporation, personal communication, November 1999).
Animal models and recent human studies suggest that VNS may enhance memory. Electrical stimulation of the vagus nerve delivered after an aversive learning experience has been shown to improve later retention performance in rats.136 In non-DD epilepsy patients, a protocol administering electrical stimulation of the vagus nerve versus sham stimulation demonstrated statistically significant higher recognition memory resulting from the former protocol.137 These studies offer hope for patients with the cognitive impairments so common among epilepsy patients.
Preliminary evidence from two studies suggests that VNS may reduce symptoms of depression in adult epilepsy patients.138,139 One study found a trend toward statistically significant reduction of dysthymic symptoms on the Cornell Dysthymia Rating Scale as compared to symptoms in control patients, although notably no significant differences were noted on other mood inventories. No correlation was seen between seizure reduction and mood improvements, but specifics of this analysis must be clarified further. Studies also are under way examining the potential role of VNS in treating primary depression in nonepilepsy patients.
Little information is available about the psychotropic effects of VNS in DD epilepsy patients. However, the aforementioned studies in nonepilepsy patients and the potential to reduce the dosage or number of AEDs given to such patients offer optimism for improving mood and cognition in this population.
Reviewed and revised June 2004 by Steven C. Schachter, MD, epilepsy.com Editorial Board.
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