Abstracts

RATIONALE: Single- and paired-pulse TMS is an emerging experimental tool for non-invasively measuring cortical excitability. Because of case reports of seizures during TMS, concern exists about the safety of performing such studies in individuals with epilepsy. However, an assessment of the true risk of a seizure has not been performed. To address this issue, we reviewed all of the published reports of TMS studies of individuals with epilepsy and calculated a numerical risk of a seizure. This review may be valuable to other researchers who use TMS to study epilepsy in human subjects.
METHODS: A PubMed literature search of [dsquote]transcranial magnetic stimulation[dsquote] and [dsquote]epilepsy[dsquote] produced 86 references. Animal experiments and review articles were excluded. The remainder of the articles were reviewed in their entirety and the following was recorded: number of epilepsy subjects exposed to single-pulse TMS technique, number of epilepsy patients exposed to paired-pulse TMS technique, number of individuals who experienced a seizure, type of seizure, recovery from seizure and timing of seizure in relationship to TMS stimulation.
RESULTS: Of the 494 epilepsy subjects who are reported to have undergone single-pulse TMS, 3 subjects had clinical seizures (1-3). The clinical events occurred immediately to 20 seconds after a stimulation. In all cases, the subjects[scquote] seizures were similar to their typical seizures and there was a full recovery to baseline. All of the subjects who had TMS-associated seizures had histories of frequent seizures, so doubt was expressed in the original reports as to whether the seizures were actually induced by TMS or a mere coincidence. The calculated risk of a seizure with single-pulse TMS in an epilepsy subject is 0.6%. None of the 114 epilepsy subjects who have undergone paired-pulse TMS had a seizure.
CONCLUSIONS: Despite the safety concerns, the risk of TMS causing a seizure in individuals with epilepsy appears small. The actual risk may be less than we report due to a greater likelihood of seizures being reported and an underreporting of the number of epilepsy subjects who have undergone TMS without incident. These findings may enable TMS epilepsy researchers to more accurately inform their epilepsy research subjects of the risk of seizure during TMS. REFERENCES: 1.Classen J et al. Electroencephalogr Clin Neurophysiol 1995; 94:19-25. 2. Hufnagel et al. Ann Neurol 1990; 27:49-60. 3. Tassinari et al. Neurology 1990; 40:1132-33.
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