The selection criteria for insertion of the NCP system remain in evolution and reflect current governmental standards, as well as institutional biases and general guidelines from prior clinical trials [1,2]. Currently, the device is only approved by the FDA "as an adjunctive therapy in reducing the frequency of seizures in adults and adolescents over 12 years of age with partial onset seizures which are refractory to antiepileptic medications'' . However, favorable results have been obtained with off-label use among children as young as age 3 and among patients with Lennox-Gastaut or other primarily generalized seizures syndromes . Preliminary experience with infantile spasms has been disappointing, however. Patients with both idio-pathic epilepsy and seizures of structural etiology are considered appropriate candidates. Of note, VNS has been used successfully among patients who have failed previous surgical procedures, confirming the potential efficacy of VNS in highly refractory patient populations.
The definition of medical intractability varies from center to center. Standards from previous studies commonly required a frequency of at least six seizures per month and a seizure-free interval of no longer than 2 to 3 weeks despite therapy with multiple medications [1,2]. However, seizure frequency, seizure type, severity of attacks, drug toxicity, and overall impact on quality of life must all be considered before a patient is deemed refractory to pharmacotherapy. Adequate monitoring of patient compliance and sufficient trials of investigational drugs must also be assured.
As noted above, the response to VNS is highly variable, and previous clinical trials have failed to characterize the demographic factors that predict a favorable outcome [1,2]. Furthermore, VNS is rarely curative. Therefore, at present, we do not consider the NCP device an alternative to conventional methods of epilepsy surgery that offer a higher likelihood of seizure cessation, and we generally reserve VNS for patients in whom such operations are not indicated. These include those patients whose seizure focus is bilateral, not associated with a structural abnormality, or cannot be completely resected because of overlap with functional cortex.
The NCP system cannot be inserted in patients who have undergone a prior left cervical vagotomy. Furthermore, the safety of VNS has not been tested in several conditions in which impairment of vagus nerve function might produce deleterious effects. Thus, relative contraindications include progressive neurological or systemic diseases, pregnancy, cardiac arrhythmia, asthma, chronic obstructive pulmonary disease, active peptic ulcer disease, and insulin-dependent diabetes mellitus .
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