Seizures from transcranial magnetic stimulation 2012–2016: Results of a survey of active laboratories and clinics

Objective: Transcranial magnetic stimulation (TMS) can cause seizures in healthy individuals and patients. However, the rate at which this occurs is unknown. We estimated the risk of seizure and other adverse events with TMS. Methods: We surveyed laboratories and clinics about seizures and other events observed between 2012 and 2016 (inclusive). Respondents (N = 174) reported an estimated 318,560 TMS sessions. Results: Twenty-four seizures were reported (.08/1000 sessions). TMS delivered within published guidelines to subjects without recognized risk factors caused 4 seizures (<.02/1000 sessions). High-frequency (>1 Hz) rTMS delivered within published guidelines to individuals without known risk factors was no more likely to cause seizures than low-frequency and single/paired-pulse TMS. Subject risk factors (e.g., brain lesions and epilepsy) increased seizure risk substantially. Seizures appeared more common when safety guidelines were exceeded. Seizures were most likely to occur within the first few exposures to TMS. Conclusions: TMS delivered within published guidelines to individuals without risk factors appears to cause fewer than 1 seizure per 60,000 sessions. The assumption that repetitive TMS is riskier than single and paired pulses under these conditions should be reevaluated. Significance: This information should help laboratories, clinics, and regulatory authorities form updated safety policies for TMS.