Six adult epileptic patients underwent rapid-rate transcranial magnetic stimulation (rTMS) at stimulation rates of up to 25 Hz with an 11-cm water-cooled round coil held flat on the scalp, centered over 15 different positions on each side of the scalp. The trains of stimuli were for 10 seconds while the patients counted aloud. rTMS centered over D5 or D7 induced reproducible speech arrest in all patients and counting errors in three when applied at lower intensities. There were no such speech disturbances by rTMS centered over the different positions on the right side. Intracarotid amobarbital test (IAT) demonstrated left hemispheric language dominance in all patients. Lateralization of speech arrest induced by rTMS correlated with the IAT results and may be helpful for noninvasive determination of hemispheric language dominance.
We retrospectively studied 474 patients seen at Hennepin County Medical Center because of medical complications related to acute cocaine intoxication. Of the 474, 403 had no history of seizures. Seizures within 90 minutes of cocaine use was the primary diagnosis in 32 (7.9%) of the 403. The majority of seizures were single, generalized, induced by intravenous or "crack" cocaine, and not associated with any lasting neurologic deficits. Most that were focal, multiple, or induced by nasal cocaine were associated with an acute intracerebral complication or concurrent use of other drugs. Of 71 patients with a history of non-cocaine-related seizures, 12 (16.9%) presented with cocaine-induced seizures; most of these were multiple, of the same type as those in their history, and induced by even nasal cocaine. In the 44 cocaine-induced seizure patients, a pattern of habitual cocaine abuse was associated with diffuse brain atrophy on CT and diffuse slowing on EEG.
We studied the effects of transcranial magnetic stimulation (TMS) applied in trains of 8- to 25-Hz stimuli on electroencephalographic epileptiform activity on eight patients being evaluated for epilepsy surgery. We performed the stimulation with a round water-cooled stimulation coil held flat on the scalp and centered over different positions of the International 10-20 System. We were unable to trigger seizures or induce epileptiform discharges arising from the epileptic focus in any of the eight patients with any of the stimulation protocols. However, we induced a partial motor seizure from the contralateral hemisphere to the exclusive temporal focus in the only patient stimulated with 100% maximal intensity. Precautions have to be taken when applying rapid TMS to patients because of the risk of seizure induction. Our results do not support the view that TMS specifically activates the epileptic foci.
Most animal studies have failed to demonstrate pathologic changes in the brain after transcranial magnetic stimulation (TMS). Nevertheless, vacuolar lesions in the cortex of rats after TMS have been reported. We report the first histopathologic studies of human brains after TMS in 2 patients with epilepsy who underwent temporal lobectomies. They had been involved in a study to determine the speech-dominant hemisphere by TMS and had received approximately 2,000 stimuli centered over the resected temporal lobe. Histologic study of the surgical specimens did not show any lesions attributable to TMS in these 2 patients.
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