Early TMS evoked potentials in epilepsy: A pilot study.

OBJECTIVE: To explore if the TMS evoked potential is different in patients with epilepsy compared to healthy subjects.

METHODS: Eighteen healthy subjects and thirteen epilepsy patients participated in this study. Single TMS pulses were applied to the left and right motor cortex. For each target we applied 75 pulses at 110% of the resting motor threshold (RMT), and continuously measured the EEG. Resting motor threshold and the TMS evoked potential (TEP) were compared between patients and healthy subjects.

RESULTS: Epilepsy patients had a higher left RMT than healthy subjects (88.5% vs. 81.8%, p=0.048). For left motor cortex stimulation, the N100 was larger in amplitude in epilepsy patients than in healthy subjects (p=0.0073). For right motor cortex stimulation, the P180 was larger in amplitude in epilepsy patients than in healthy subjects (p=0.006). The differences in these late TEP components were localized in the centro-parietal areas. No significant differences were found for other TEP components.

CONCLUSIONS: In this pilot study, we found a significant higher MT and higher TEP amplitudes in epilepsy patients compared to healthy subjects.

SIGNIFICANCE: Changes in cortical excitability may assist in epilepsy diagnostics or evaluation of the efficacy of anti-epileptic drugs.