DOI: 10.1097/YCT.0b013e3181e6336e
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PMID: 21602643
Issn Print: 1095-0680
Publication Date: 2011/06/01
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Excerpt
Kratz et al1 reported the possible induction of a seizure with single-pulse transcranial magnetic stimulation (spTMS) in a healthy adult male volunteer. As the authors point out, spTMS has never been reported to cause a seizure in a normal healthy individual since its introduction in 1985.2 Therefore, given the implications of this finding, it is critical to carefully consider the details of the event.
The essential question is whether the participant really had a seizure. From the available information, we believe that the event lacks unequivocal features to be diagnosed as a seizure, and thus, the title, the abstract, and the conclusions of the authors have the potential to mislead readers. Many of the reported signs and symptoms suggest convulsive syncope as the most likely cause of this event. First, the episode started with nausea. This symptom is considered of high diagnostic value to exclude a seizure,3 with an estimated specificity of 94% to 98%.4 Nausea may occur in certain partial seizures, but typically not in those originating from the left motor cortex, the location over which TMS was being delivered in the subject. Second, the episode of alteration of consciousness was brief and was not followed by postictal confusion. Third, incontinence has little diagnostic value in discriminating between seizure and syncope.3-5 Fourth, the description of involuntary movements during the episode, with asymmetric twitching of both arms and emphasis of the left hand, suggests a right-hemispheric origin, inconsistent with the TMS-targeted left motor cortex. Furthermore, movements that take place during a seizure typically have a synchronous and rhythmic pattern. Also, the subject had "rearing up," which suggests a more nonspecific movement, compared with turning of the head, which might be more specific for a seizure.5
Involuntary, convulsive movements are commonly observed during a syncopal event as a consequence of cerebral hypoxia. The movements may have different manifestations, for example, up to 46% of blood donors having a vasovagal reaction may experience tetany, clonic movements, and twitching.4 The patient of Kratz et al seemed to have remained upright in his seat the whole time, and that could have increased the chances of syncope being associated with convulsive-appearing activity because of the prolonged cerebral hypoperfusion. However, this condition-convulsive syncope-is not due to primary, epileptic discharges.
Even if this event represented a seizure, then the risk of seizure with spTMS is still exceedingly low, certainly lower than 1:100,000 because practically all subjects receiving any form of TMS (single-pulse, paired-pulse, or repetitive) undergo spTMS determination of motor threshold, as what purportedly triggered the spell in the present case. Given that very low risk, we think that the overall safety recommendations2 should not be affected by the present report.
We suggest that the biggest lesson to be learned from this report should be that, in cases of possible presyncopal symptoms, TMS participants should be made to recline immediately. In addition, as Kratz et al suggested, subjects should be screened for potential factors that predispose to syncope, and the risk of syncope should be disclosed to participants as part of the informed consent. Finally, reports of these types of TMS-induced events should contain as much detail as possible to enable a critical differential diagnosis, and we should avoid labeling all events as epileptic seizures.
