Safety of single and repetitive focal transcranial magnetic stimuli as assessed by intracranial EEG recordings in patients with partial epilepsy

The safety of single and repetitive (paired and quadruple) focal transcrani al magnetic stimuli as possible inducers of epileptic discharges or clinica lly manifest seizures was investigated in 21 patients with intractable epil epsy during invasive presurgical monitoring. Subdural and/or intracerebral depth electrodes had been implanted in close proximity to the suspected epi leptogenic zone, and the anticonvulsant medication had been reduced. Focal transcranial magnetic stimuli were applied by a Magstim QuadroPulse magneti c stimulator over the hand area of the motor cortex ipsilateral to the epil eptogenic focus at intensities of 120% and 150% of motor threshold and addi tionally as close as possible to the suspected epileptogenic zone at 40-100 % of maximal stimulator output. Stimulation did not induce any complex part ial of secondary generalized tonic-clonic seizures. One patient with hippoc ampal sclerosis experienced an aura associated with rhythmic electroencepha lographic discharges restricted to the ipsilateral intrahippocampal depth e lectrode after stimulation over his left temporal lobe. This patient, howev er, also had frequent spontaneously occurring auras with focal ictal discha rges originating from this hippocampus. Interictal discharges were not infl uenced significantly by single or repetitive magnetic stimuli. In conclusio n, from this study there is no evidence that single or serial focal transcr anial magnetic stimuli activate epileptogenic foci. At least four high-freq uency repetitive stimuli of high intensity may thus be applied with a low r isk of seizure induction even in patients with low seizure threshold.