Abstracts

The published prevalence of epilepsy in dogs varies from 0.5% to 5.0%. The purpose of this study was to investigate the role of single-pulse transcranial magnetic stimulation (s-TMS) in the evaluation of the threshold intensity (TI) in healthy mature control dogs and in dogs suffering from refractory idiopathic epilepsy. The study also evaluated the effect of s-TMS on the seizure frequency of dogs with refractory idiopathic epilepsy. Five healthy mature beagles (control group) and nine client-owned epileptic dogs refractory to AED treatment (epileptic group) were studied. The epileptic group included dogs receiving single or multiple AEDs. No treatment change was made in the two months prior to and following the study. Affected dogs were followed for at least 60 days before and after TMS. A calendar of the seizures was kept to evaluate the interval between seizures and number of seizures before and after TMS. Single-pulse TMS was performed by delivering five consecutive stimulations on each side of the cortex, and lumbar area. The intensity of stimulation was gradually increased (5% each time) from 30% to 90% of maximal coil output. Motor evoked potentials (MEPs) were recorded from the tibialis cranialis muscle contralateral to the stimulated cortex, and ipsilateral to the stimulated lumbar site. TI was defined as the lowest stimulation intensity required to evoke at least 2 reproducible MEPs of amplitude greater than 50uV from 5 consecutive stimuli. A Pooled Student t-test and Wilcoxon-Mann-Whitney test were used for statistical analysis. Statistical significant differences were observed in the TIs after cortical (p=0.037) and lumbar (p=0.059) stimulations between control (39.5+/-3.82% cortical and 40.0+/-3.65% lumbar) and epileptic groups (56.6+/-2.85% cortical and 47.5+/-2.72% lumbar) (fig.1). In the epileptic group, five out of nine dogs were reported to have short-term improvement of the seizure interval in the post-TMS period as compared to the pre-TMS period. Overall, six out of nine epileptic dogs had a reduced number of seizures in the post-TMS period versus the pre-TMS period. Cortical and lumbar TIs following s-TMS were determined in healthy mature control dogs. Epileptic dogs treated with AEDs had decreased cortical excitability compared to healthy non-treated dogs. Treatment with s-TMS was observed to prolong the number of days without a seizure and to decrease the total number of seizures in treated epileptic dogs for a limited period time suggesting the potential short-term beneficial effect of TMS in canine refractory epilepsy.[figure1] (Supported by Pet Trust Foundation, University of Guelph.)