Cognitive function during vagus nerve stimulation (VNS) for treatment-refractory epilepsy: a Pilot Study using the Critical Flicker Fusion (CFF) Test
Aims
To explore the neuro-cognitive effects of VNS in patients with treatment-refractory epilepsy using the Critical Flicker Fusion (CFF) Test, a neuropsychological measure of cognitive integrative capacity of the central nervous system.
Methods
Consecutive adult patients with treatment-resistant epilepsy referred to the Epilepsy VNS Implantation Programme at two regional University Hospitals in England were approached. Seven patients entered this pilot study with a prospective design. Observations were recorded at baseline and after 12 months of VNS treatment. All participants completed standardised self-rated behavioural measures, including the Hospital Anxiety and Depression Scale (HADS) and the Quality of Life in Epilepsy Scale (QOLIE-10), as well as automated neuropsychological tests of attention, concentration, memory, logical thinking and cognitive integrative capacity (CFF Test). Participants were required to keep accurate seizure diaries throughout the duration of the study.
Results
The group as a whole showed a significant improvement in seizure frequency at 12 months (p=0.05), with three participants reporting a >50% reduction in overall seizure frequency. VNS treatment also resulted in a significant improvement in the “seizure worry” and “memory” domains of the QOLIE-10 (both p<0.05) and a trend towards reduction in the severity of anxiety symptoms measured by the HADS (p=0.107). Neuropsychological testing showed a trend towards improvement in visual recognition and logical thinking, attention and concentration, and memory, however none of these changes were statistically significant. On the other hand, the group as a whole showed a significant improvement in CFF Test scores (p<0.05).
Conclusions
This prospective pilot study suggests that the CFF Test can be a useful and sensitive tool in detecting subtle cognitive enhancement in patients with refractory epilepsy successfully treated with VNS.
