The Effectiveness Of Vagus Nerve Stimulation (VNS) Therapy For Drug-resistant Epilepsy

Epilepsy is a disease that caused by the synchronized and limited p aradoxicaldischarge with many causes. It is characterized by recurrent, transient, repetitive andstereotyped functional disorder of central nervous system. An estimated50million peopleworldwide are affected by epilepsy, most of who are successfully tr eated with single ormultidrug regimens. The drug-resistant epilepsy has been reported to occur in20%to30%of patients with epilepsy and can be devastating to patients and their families. What’smore, this brings patients with epilepsy suffer the mental disorders and causes lots ofsocietal problems. The novel antiepileptic drugs (AEDs) and the adjuvant drugs couldbecome options for the drug-resistant epilepsy when the patient demonstrate a poorresponse to the orthodox treatment. The drug-resistant epi lepsy is the main i ndications forsurgical procedures. The surgical approaches depend on the preoperative assessment.There are many kinds of surgical treatment for drug-resistant epilepsy, including resectivesurgery, disconnection procedures, devastating surgery and stimulation procedures. Thestimulation procedures include deep brain stimulation (DBS) and vagus nerve stimulation(VNS).Vagus nerve stimulation has been in use since U.S. Food and Drug Administration(FDA) approval in July16,1997, for the palliative treatment of drug-resistant epilepsy.The effectiveness of VNS was more and more confirmed. This palliative treatmentperformed in more than800thousand patients from75countries, and more than100thousand patients experienced this therapy. The efficacy and safety of VNS need to be evaluated in China. And VNS therapy wasidentified as “domestic advanced level” in the department of neurology in China. As aresult, we retrospectively reviewed a database prospectively created with19patients, w hounderwent vagus nerve stimulator implantation for drug-resistant epilepsy betweenOctober2010and December2012. The generator was turned on two or three weeks afterthe plantation operation. We adjusted the stimulation parameters gradually. The outputcurrents were adjusted from0.25mA, stimulative time was30s signal-ON and5minsignal-OFF, the frequency was30Hz, and the pulse width was500μs Then the changeof the output currents was0.25mA every1-3months. And the magnet turned on when theoutput currents were0.75mA. The magnet currents were over0.25mA than the outputcurrents, and the stimulative time was60s signal-ON and5min signal-OFF, the frequencyand the pulse width remained unchanged. All patients in the primary implantation gr oupwere follow-up (≥3months from implantation) adequately, so as to assess the efficacy andsafety of vagus nerve stimulation therapy for drug-resistant epilepsy.Duration of vagus nerve stimulation treatment varied from3to29months (median:15months). Seizure freedom was achieved in10patients (52.5%), Seizure control≥90%was achieved in11patients (57.9%),≥75%seizure control in12patients (63.2%),≥50%improvement in16patients (84.2%), and <50%improvement in3patients (15.8%).10patients had improved Engel class I;1had improved Engel class!a;5had improved Engelclass!b and3had improved Engel class IV outcomes.12patients had McHugh class IA;1had improved McHugh class!a A;3had improved McHugh class!a B and3had improvedMcHugh class!d outcomes. The output currents were0.25mA in5patients,0.75mA in3patients,1.0mA in5patients,1.25mA in one patient,1.5mA in3patients,2.0mA in2patients. There is no change of antiepileptic drugs (AEDs) in14patients; reduction ofAEDs in4patients; increase of AEDs in one patient.15.8%patients reported one transientmild adverse effect, respectively.Vagus nerve stimulation is a safe and effective palliative treatment for drug-resistantepilepsy. The key to the effectiveness of vagus nerve stimulat ion is adjusting the rightparameters to each patient. The parameter adjustment of VNS is based on patient pro fles.Low stimulative parameters maybe achieved great effectiveness. We believe betterseizures control can be achieved as long as allowing more titration of the stimulationparameters and further AEDs regimen adjustments over time by the qualifiedepileptologists.