Transcranial Magnetic Stimulation (TMS) is a non-invasive brain stimulation therapy for mental health conditions like depression, using magnetic fields to stimulate brain nerve cells. Individuals considering TMS often wonder about its safety, specifically concerning the potential for seizures. This article provides evidence-based insights into that risk.
Understanding Seizure Risk with TMS
TMS can cause seizures, but this is very rare, especially when safety guidelines are followed. The overall risk of a TMS-related seizure is generally less than 1%. A survey of over half a million TMS sessions reported a seizure rate of 0.31 per 10,000 sessions and 0.71 per 1,000 patients. This risk is comparable to, or even lower than, the seizure risk of many commonly prescribed psychotropic medications.
Most TMS-induced seizures are self-limiting, resolving without lasting complications. The low incidence rate reflects careful protocols. The majority of these rare events occurred during high-frequency repetitive TMS (rTMS) at higher intensities or with longer stimulation durations. Even individuals with a history of epilepsy have undergone TMS without experiencing seizures, underscoring its safety when properly managed.
Factors Influencing Seizure Susceptibility
Several individual characteristics and physiological states can influence susceptibility to a TMS-induced seizure. Pre-existing neurological conditions significantly elevate this risk. Individuals with a history of epilepsy, head trauma, or brain lesions are more likely to experience a seizure during TMS therapy, as these conditions alter brain excitability.
Certain medications lower an individual’s seizure threshold, increasing the risk during TMS. These include some antipsychotics, lithium, clozapine, and certain antidepressants. While bupropion has been historically associated with seizure risk, current data suggest it is not an absolute contraindication for TMS when proper safety measures are in place. Substance use, particularly excessive alcohol intake or recent alcohol withdrawal, can also significantly increase seizure susceptibility.
Other transient factors that can heighten the risk include sleep deprivation. The specific parameters of the TMS treatment itself, such as very high stimulation intensity or prolonged stimulation trains, can also contribute to an increased risk. Some coil types, like the H-coil, have been associated with a higher seizure risk compared to the more commonly used Figure-8 coils, likely due to a broader stimulation field.
Mitigating Risk Through Safety Protocols
Clinicians employ safety protocols to minimize seizure risk during TMS therapy. A thorough patient screening process is fundamental, beginning with a detailed medical history and neurological examination. This assessment helps identify any pre-existing conditions, medications, or lifestyle factors that might increase seizure susceptibility. Patients complete a specialized TMS Safety Questionnaire to identify and address potential risks.
Precise determination of stimulation parameters is another safety measure. Before treatment, a “motor threshold” is determined for each patient. This is the minimum magnetic field intensity required to elicit a small muscle twitch. This individualized threshold guides the treatment intensity, usually set between 110-120% of the motor threshold, to ensure safety. Adherence to international safety guidelines, such as those from the International Federation of Clinical Neurophysiology (IFCN), is followed to prevent overstimulation.
During the TMS session, trained operators monitor the patient in real-time. Emergency procedures are in place, ensuring staff are prepared to respond immediately in the rare event of a seizure. These safety measures, from initial patient evaluation to precise treatment delivery and continuous monitoring, reduce the risk of adverse events and ensure patient well-being.