Abstracts

Rationale: Vagal nerve stimulation is seen in patients with pharmacoresistant epilepsy who are not eligible for resective epilepsy surgery or for whom the resective surgery failed. Progressive loss of memory occurs frequently in temporal lobe epilepsy. Besides its use in epilepsy treatment, the VNS has been under investigation as a therapy for memory impairment in Alzheimer's disease. Hoppe et al (2001) did not find any VNS effect on short-term memory, learning and memory, and executive functions in a 6 month study. In this study we explored the long-term impact of VNS on memory functions. Methods: We analysed 27 patients (12 male, 15 female) with VNS who have been treated at the Epilepsy Center in Brno. We have prospectively followed up patients who had been evaluated within an epilepsy surgery program using the ictal video-EEG and advanced imaging methods; however, they were not eligible for the surgery. Temporal epilepsy has been diagnosed in 11 patients, extratemporal epilepsy in 8 patients; a mesio-temporal sclerosis (MTS) has been diagnosed in 8 patients. Mean duration of epilepsy was 25.96 (range 4 - 50) years. Mean age of the VNS implantation was 35.59 (range 17 - 59) years. All patients were evaluated by the Wechsler III memory test before the VNS implantation and 5 - 10 years after. We evaluated seizure frequency both before and after the VNS implantation. Results: The mean MQ before the implantation was 90.77 (SD=16.48), and dropped significantly to 80.22 (SD=16.09) (F(d.f.=1,26)=18.79; p<0.001) after the implantation. The value decreased in 22 of 27 patients (5 have not changed). The decrease ranges from 4 to 36 points of MQ. The MQ decrease was not significantly related to patients‘ age at the time of the VNS implantation (r=-0.237; p=0.235). There was no significant difference between patients with MTS and without MTS (MWU=65; p=0.314), or between the responders (12) and non-responders (15). However, the MQ before implantation correlates with the MQ change. The patients with a higher pre-implantation MQ declined more than those with a lower MQ (r=-0.414; p=0.32). The MQ decreased significantly in the verbal immediate memory domain (91.3 (SD22.66) - 75.66 (SD20.40) (F(d.f.=1,20)=22.99; p<0.001). Eighteen of 21 patients with available data have declined. The mean score of verbal delayed memory remained unchanged (86.6 (SD27.5) before and 86.15 (SD18.15)) after the implantation. No significant decreases of both visual immediate and delayed memory scores were present, even though the sample mean decreased from 86.89 (SD16.81) to 77.84 (SD16.76) in visual immediate memory (13 of 19 patients), and from 88.82 (SD20.74) to 77.58 (SD17.85) in delayed visual memory score (13 of 17 patients). Conclusions: Impaired memory is a common feature in patients with pharmacoresistant epilepsy. In our study, we have not found any positive effect of long-lasting VNS stimulation on memory development in epilepsy. On the contrary, in 75% of patients, the memory decline continued during the 5-10 years with vagal nerve stimulation.