Abstracts

Because low frequency transcranial magnetic stimulation of the cerebral cortex is reported to decrease cortical excitability and seizure frequency, we delivered low frequency electrical stimulation through subdural strips to determine whether it also may reduce seizure frequency in a case of refractory status epilepticus.
A previously healthy 26-year-old female was admitted after one day of confusion and 6 days of fever, cough and emesis. She had 2 generalized tonic-clonic seizures on the day of admission and 4 on the following day. Head CT, spinal tap, and brain MRI/MRS were unremarkable. Six days after admission, she developed successive seizures, ultimately requiring intubation and pentobarbital. EEG was kept in burst suppression for 3 months. Seizure control required continuous infusion with 2 anesthetics in addition to high doses of 2 to 4 enteral antiepileptic drugs (AEDs). Scalp EEG monitoring revealed bilateral periodic epileptiform discharges, which were associated with right jaw and right neck twitching, and frequent left occipital seizures, which were associated with eye blinking. An ictal FDG-PET revealed marked hypermetabolism in the left occipital lobe with patchy areas of hypermetabolism in the left parietal and right occipital lobes. A methohexital suppression test demonstrated seizure suppression with a left but not a right ICA injection. In search of a resectable focus, subdural strips were placed with 108 contacts across bilateral hemispheres with greater coverage on the left. Five independent ictal onset zones were identified: right occipital (44% of seizures), left temporoparietal (27%), focal left occipital (12%), broad left occipital (14%), and right frontal (3%). Stimulations at 0.5 Hertz were administered to the ictal onset zones. Biphasic 0.5ms duration stimulations were given in 30-minute trains every day for 7 consecutive days at an intensity of 2-4 milliamps per electrode pair.
After one day of stimulation, propofol was successfully discontinued without recurrence of seizures. Seizures remained absent for the following 4 days, and returned when midazolam had been reduced by 60%. Upon returning, the left occipital region was the only ictal onset zone. The other regions remained seizure free. Subsequently a left occipital resection was performed, but it was not efficacious. The patient died 2 months later. Pathology was consistent with chronic global anoxic encephalopathy.
In this case of refractory status epilepticus, low frequency electrical stimulation through subdural strips suppressed the seizures from all but one ictal onset zone, and allowed significant reduction in seizure medication. Focused low frequency stimulation of the cerebral cortex may be useful in suppressing seizures.