Abstracts

RATIONALE: Cortical stimulation is usually performed as part of the invasive neurophysiological investigation in patients with refractory extratemporal epilepsy and normal or non-localizing MRI submitted to subdural electrodes implantation.
METHODS: Twenty patients with refractory extratemporal epilepsy and normal or non-localizing MRI submitted to extensive coverage of the brain surface with subdural electrodes were studied. Four patients had anterior quadrant, 3 posterior quadrant, 5 hemispheric, 4 rolandic and 4 bifronto-mesial epileptic syndromes. The number of electrodes ranged from 64 to 256. Mean follow-up time was 1,6 years. Cortical stimulation was carried out in the awaken patient with square pulses at 100 Hz, 0,1 msec of duration and 4-8 mA.
RESULTS: The patient[prime]s habitual seizures could be triggered by stimulation of 1-3 electrodes in 13 out of 20 patients. In 1 patient with supplementary motor area (SMA) epilepsy, seizures could be elicited from both SMA areas. Overall, 75% of the patients were rendered seizure-free by surgery. Ninety-three percent of the patients in whom the habitual seizures were obtained during cortical stimulation have been seizure-free while 40% of the patients in whom no seizures were triggered did so. There was no major neurologic morbidity or mortality related to cortical stimulation.
CONCLUSIONS: Cortical stimulation is safe and very effective in triggering the patients habitual seizures when an extensive coverage of the brain surface was used. Misdiagnosis or failure to induce seizures are very likely to occur in patients with limited or erratic coverage of the cortical surface with invasive electrodes. Seizures were generally elicited from a very small number of electrodes. Patients in whom the habitual seizures were elicited by cortical stimulation had a better surgical outcome.
[Supported by: Sao Paulo Secretary of Health]