Abstracts

Rationale: Transcranial magnetic stimulation (TMS) is a method for focal noninvasive cortical stimulation where small intracranial electrical currents are generated by a powerful extracranial fluctuating magnetic field. Navigated transcranial magnetic stimulation applied in single pulses and short trains of high frequency repetitive stimulation are FDA-approved methods for noninvasive presurgical mapping of both the motor and language cortex. The rationale of the current study is to assess the safety and tolerability of this procedure in children with epilepsy as this has not previously been established.Methods: A high-resolution MRI scan was acquired prior to TMS and used to guide and document the stimulation targets with a frameless stereotaxy system. A figure of eight coil was used to apply single-pulse TMS at 100-110% of resting motor threshold (rMT) along the precentral gyrus and surrounding cortex for motor mapping. rTMS at 90-110% rMT was delivered in 1-second 5 Hz trains to the regions surrounding the inferior frontal gyrus in both the left and right hemispheres for language mapping. Adverse events were documented during each session.Results: 59 patients underwent TMS motor mapping, and 12 patients underwent rTMS language mapping. There were no instances of atypical seizure, status epilepticus or epilepsy exacerbation. A typical seizure occurred in 3 of 59 patients with epilepsy during motor mapping, and no seizure occurred in patients undergoing language mapping. Of the three instances of in-session seizure during motor mapping, one occurred in a setting of reduced antiepileptic medications, and a second occurred in a patient who typically experienced frequent daily seizures. A third seizure occurred without additional provoking factors. Other adverse events were mild and short-lived: headache and facial pain in all patients during language mapping, likely due to the anterior placement of the stimulating coil. Another source of discomfort, present on both motor and language mapping studies, was headache attributed to the elastic headband that is worn throughout the procedure, which has resolved spontaneously after the TMS session.Conclusions: Navigated TMS functional mapping, even by repetitive stimulation protocols, which in principle may increase the risk of seizure provocation, is relatively safe and tolerable in children with drug-resistant epilepsy.