engleski

Vagus nerve stimulation – minimally invasive neurosurgical treatment in patients with pharmacoresistant epilepsy: our experiences

Background and aim: Vagus nerve stimulation (VNS) for the treatment of refractory partial epileptic seizures with or without secondary generalisation in adolescent and adult patients (older than 12 years) was approved in Europe in 1994 and in the United States in 1997. In several studies performed in the last years, that included patients with Lennox-Gastaut syndrome (LGS), there was also statistically significant decrease in seizure frequency. The precise mode of action of VNS is still not known, however, various studies have suggested that VNS acts through 1) direct afferent projections - increases seizure threshold through connections with nucleus tractus solitarii ; 2) modulation of neurotransmiters - widespread release of GABA and glycine ; 3) neural ''network'' regulation. We have studied the efficacy of VNS in patients with pharmacoresistant epilepsy hospitalized in the Department of Neurology and Neurosurgery of the Zagreb University Hospital Centre. Methods: From 1997 do 2001 we have implanted vagus nerve stimulator (the NeuroCybernetic Prosthesis /NCP/ system) in 11 patients with pharmacoresistant epilepsy (6M, 5F), mean age 26.62 ± ; 4.93, who were magnetic resonance imaging (MRI) negative and from May 2007 to July 2009 in 11 patients with pharmacoresistant epilepsy (5M, 6F), mean age 30.61 ± ; 12.76, who were MRI positive, and were inoperable due to localisation of the pathomorphologic changes (ganglioglioma, hamartoma, various types of cortical dysplasia, porencephalic cysts). In the group of MRI negative patients 1 patient had complex partial seizures (CPS), 5 patients had CPS with secondary generalisation, 2 patients had primary generalized epilepsy (PGE) including myoclonic, absence, atonic and tonic-clonic seizures, and 3 patients had LGS. In the group of MRI positive patients one patient had elementary partial seizures (EPS) and CPS, two patients had EPS and CPS with secondary generalisation, one patient had CPS, 5 patients had CPS with secondary generalisation, and 2 patients had CPS with secondary generalisation as well as atonic seizures. Intensity of the stimulation in the group of MRI negative patients was from 0.75 to 2 mA, and in the group of MRI positive patients from 0.50 to 2 mA. The duty cycle was, in the group of MRI negative patients, set to 30-Hz signal frequency, 500-μ s pulse width, 30 seconds on-time, and 5 minutes off-time. In the group of MRI positive patients all parameters of the duty cycle were the same, except the off-time, that was set to 60 minutes. After VNS implantation there was no reduction in the dose and number of antiepileptic drugs. Results: After continuous follow-up of 11 MRI negative patients during 5 years there was decrease in mean-seizure frequency of 73.37%. Two patients with LGS were completely seizure free after VNS implantation. After continuous follow-up of 11 MRI positive patients during 2 years there was decrease in mean-seizure frequency of 61.9 %. The most frequent side effects were hoarseness, throat pain and cough in the “ on phase” of the stimulator, but they were mild and transitory. Conclusion: VNS was effective mode of therapy in our group of patients with pharmacoresistant epilepsy. Since the second group of patients did not show so good results considering reduction of seizure frequency after VNS implantation compared to the first group, we think that the cause is new algorithm of stimulation. In the first group off-time was set to 5 minutes, and in the second group to 60 minutes. We can also speculate that the MRI positivity could have some influence on the results. In the future we are planning to set off-time to 30 minutes or lower in all patients.

vagus nerve stimulation; pharmacoresistant epilepsy

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