Abstracts

Rationale: Previous research in drug naïve epilepsy patients reports that those who become seizure free after commencing their first antiepileptic drug (AED) show a reduction in transcranial magnetic stimulation (TMS) measures of cortical excitability when assessed 4-16 weeks after starting the drug. This is in contrast to patients who go on to be refractory, who show no significant changes from baseline (Badawy et al., 2010). The aim of this study was to assess whether TMS measures of cortical excitability predict treatment outcome in chronic refractory medicated patients, when changing AEDsMethods: Thirty three patients with chronic medically refractory epilepsy who were starting a new AED were recruited. Using electromyography, Motor Evoked Potentials were recorded from the first dorsal interosseus muscle. TMS was delivered to the contralateral motor cortex. Wherever possible motor threshold (MT), cortical silent period (CSP) and paired pulse measures of short-interval intracortical inhibition (SICI), long-interval intracortical inhibition (LICI) and intracortical facilitation (ICF) were recorded from both hemispheres at baseline and again a few weeks after commencing the new AEDResults: Twenty two patients continued their AED, with six showing a good response. Eleven patients from the thirty three withdrew before the follow up study for reasons including AED being ceased due to side effects or worsening of seizures. It was only possible to obtain a full dataset of paired pulse measurements in both hemispheres at baseline and follow up in 9 patients due to very high thresholds; a full dataset at baseline and follow up was obtained in 13 patients in the right hemisphere. There was lower cortical excitability in those who showed a poor response to AED change, which did not differ between baseline and follow-up, although was significant only at follow up (increased right SICI (p=0.006) and reduced right ICF (P=0.019)). There was a greater increase in right LICI between baseline and follow-up sessions in those who showed a poor response to the AED change (p= 0.042).Conclusions: Despite some evidence of differences between good and poor outcome groups, our study suggests that TMS would not have good utility as a clinical predictive marker of AED change in chronic medically refractory epilepsy: 33% of the patients studied at baseline withdrew from the study before the follow up session, mainly due to side effects or due to exacerbation of seizures, furthermore the paired pulse measures could only be obtained both at baseline and follow up in 25% of those initially recruited. This would inevitably not be cost effective. There were several small effects which mostly indicated, in contrast to the work of Badawy et al., that cortical excitability is reduced in those who show a poor response to AED change. The reasons for this are not yet clear. BADAWY, R. A. B., MACDONELL, R. A. L., BERKOVIC, S. F., NEWTON, M. R. & JACKSON, G. D. 2010. Predicting seizure control: Cortical excitability and antiepileptic medication. Annals of Neurology, 67, 64-73.