Abstracts

Vagus nerve stimulation (VNS) has been established as a safe and effective strategy in the treatment of epilepsy. Most studies have explored its efficacy in terms of seizure reduction. Only a very small number of studies have evaluated the cognitive outcome associated with VNS. A few studies suggest VNS may be associated with improvements in particular cognitive functions, including reaction time/attention (Clarke et al., Can. J Neurol Sci, 1997, 24, 226-229; Dodrill [amp] Morris, Epilepsy Behav, 2001, 2, 46-53) and memory (Clark et al., Nature Neurosci 2001, 2, 94-98); other research has failed to find cognitive changes (Hoppe et al., Epilepsy Behav, 2001, 2, 351-356).
We report preliminary findings from a prospective study examining cognitive changes associated with VNS in patients with refractory epilepsy. Each participant (N = 8) underwent a comprehensive neuropsychological evaluation both prior to VNS implantation and at 6 months follow-up. Areas assessed included attention, language, memory, visuoperceptual abilities, and executive functioning. To help control for practice effects two alternate forms of the memory measures were used at each testing interval. Because of the small sample size and the relatively large number of variables, statistical significance was set at .01.
Paired sample t-tests were used to assess changes in the cognitive scores from baseline to follow-up. Of the four memory indices, two showed a statistically significant improvement at follow-up (ps [lt] .001); another memory test showed a trend for improvement (p = .04). Three of four measures of attention showed significant improvement at follow-up (ps [lt].005). No measures of visuospatial processing or executive functioning were significantly different at follow-up. Of the three language tests, two showed no significant change, but patients performed more poorly on a confrontation naming tests after treatment (p = [lt].001).
Results suggest the VNS may be associated with mild improvements in attention and memory. Although some researchers have argued that changes in cognitive scores are a function of practice effects, we found that even when using alternate forms of a memory tests (to help control for practice effects) there was evidence of improved memory performance over the course of treatment. Other cognitive domains were unaffected. The reason for decline in one of three language tests is unclear; no previous studies have examined this variable. Given the number of statistical comparisons, it is possible that this is a spurious finding. There are a number of limitations to the study. Because of the small sample size we could not examine how degree of seizure control relates to cognitive outcome. Additionally, although statistically significant improvements on select cognitive tests were found, the clinical relevance of such findings to patients[rsquo] daily functioning and quality of life needs further study.
[Supported by: Cyberonics]