Optimum duration of hyperventilation during electroencephalography.

Hyperventilation (HV) is carried out for 3 minutes as a standard activation procedure in most routine electroencephalographic (EEG) procedures. The cerebral blood flow (CBF) reduction and the accompanying cerebral vasoconstriction caused by HV is believed to be the mechanism of EEG activation during HV. Some advocate for 5 minutes of HV, although the optimum duration is unknown. In this study, we measured the CBF continuously over the anterior temporal lobes using subdural probes, which use thermal diffusion flowmetry to measure CBF directly from the cerebral cortex. We sought to determine the duration of HV that produces the maximum reduction in CBF during routine HV in our epilepsy monitoring unit and prolonged the procedure for an additional 2 minutes for this study. Flowtronics® CBF probes were placed over the anterior temporal lobes in addition to the standard subdural strip placement for localization of their seizure focus in six patients who were candidates for epilepsy surgery. CBF was measured continuously for 2 minutes before and 5 minutes during HV for each patient. Time to reach maximum reduction of CBF for each attempt (11 temporal lobes) was computed. At 3 minutes, CBF reduction ranged from 11.6% to 40.0% from the pre-HV CBF level (mean 23.9%). At 5 minutes, CBF ranged from 14.3% to 42.0% (mean 25.7%). Six of the 11 measurements were steady or decreased slightly, and in the five other measurements, CBF showed a reverse trend after 3 minutes. A significant CBF reduction was attained in 3 minutes of HV in all trials. Continued HV after 3 minutes resulted in only a marginal (mean 1.8%) additional CBF reduction after 3 minutes. Thus, we propose that 3 minutes of HV is sufficient for EEG activation by the CBF criterion.

Cerebral blood flow dynamics before, during, and after seizures from epilepsy and the periictal state.

Changes in cerebral blood flow (CBF) in the human cerebral cortex during surgery were reported by Penfield. However, data on continuous CBF during seizures were not available until Carter et al developed a subdural CBF probe for measuring continuous CBF. This probe used thermal resistor methodology and was developed to study patients with head trauma. With such a probe, changes in continuous CBF and electroencephalography during and after a seizure were reported by Oommen et al. Such changes were later confirmed examining the same phenomenon by using cerebral perfusion with laser Doppler methodology with epidural electroencephalography. This review details the evolution of our knowledge of CBF from observational reports to recordings from the animal and human cortices, by varying methodologies.

Electrical stimulation of the anterior nucleus of thalamus for treatment of refractory epilepsy.

PURPOSE: We report a multicenter, double-blind, randomized trial of bilateral stimulation of the anterior nuclei of the thalamus for localization-related epilepsy. METHODS: Participants were adults with medically refractory partial seizures, including secondarily generalized seizures. Half received stimulation and half no stimulation during a 3-month blinded phase; then all received unblinded stimulation. RESULTS: One hundred ten participants were randomized. Baseline monthly median seizure frequency was 19.5. In the last month of the blinded phase the stimulated group had a 29% greater reduction in seizures compared with the control group, as estimated by a generalized estimating equations (GEE) model (p = 0.002). Unadjusted median declines at the end of the blinded phase were 14.5% in the control group and 40.4% in the stimulated group. Complex partial and "most severe" seizures were significantly reduced by stimulation. By 2 years, there was a 56% median percent reduction in seizure frequency; 54% of patients had a seizure reduction of at least 50%, and 14 patients were seizure-free for at least 6 months. Five deaths occurred and none were from implantation or stimulation. No participant had symptomatic hemorrhage or brain infection. Two participants had acute, transient stimulation-associated seizures. Cognition and mood showed no group differences, but participants in the stimulated group were more likely to report depression or memory problems as adverse events. DISCUSSION: Bilateral stimulation of the anterior nuclei of the thalamus reduces seizures. Benefit persisted for 2 years of study. Complication rates were modest. Deep brain stimulation of the anterior thalamus is useful for some people with medically refractory partial and secondarily generalized seizures.

Epileptic Seizure Detection and Prediction Based on Continuous Cerebral Blood Flow Monitoring--a Review.

Epilepsy is the third most common neurological illness, affecting 1% of the world's population. Despite advances in medicine, about 25 to 30% of the patients do not respond to or cannot tolerate the severe side effects of medical treatment, and surgery is not an option for the majority of patients with epilepsy. The objective of this article is to review the current state of research on seizure detection based on cerebral blood flow (CBF) data acquired by thermal diffusion flowmetry (TDF), and CBF-based seizure prediction. A discussion is provided on the applications, advantages, and disadvantages of TDF in detecting and localizing seizure foci, as well as its role in seizure prediction. Also presented are an overview of the present challenges and possible future research directions (along with methodological guidelines) of the CBF-based seizure detection and prediction methods.

The relative localizing value of interictal and immediate postictal SPECT in seizures of temporal lobe origin.

UNLABELLED: Although interictal hypoperfusion and ictal hyperperfusion are established localizing findings in partial epilepsy, their relative value is disputed. After a meta analysis of several published articles on SPECT brain imaging in patients with epilepsy (with extractable data on at least 6 patients per article), institutions using SPECT for evaluation of epilepsy have been encouraged to perform ictal scanning or interictal and postictal SPECT studies. METHODS: We compared the relative localizing values of hypoperfusion in video-electroencephalographically (EEG) monitored interictal SPECT (IISPECT) and hyperperfusion in immediate postictal or periictal SPECT (PISPECT) in nonlesional patients who underwent temporal lobectomies in our epilepsy center from 1995 to 1998. We also evaluated the usefulness of combined interpretation of IISPECT and PISPECT when available. RESULTS: Our experience with continuous cerebral blood-flow monitoring, published elsewhere, and SPECT results indicate that these recommendations are valid, but obtaining ictal SPECT is often serendipitous. We found that (a) interictal hypoperfusion was easier to demonstrate by SPECT but was less often concordant with the EEG focus than hyperperfusion in PISPECT, but not significantly (P = 0.11) so; (b) the lower incidence of hyperperfusion in PISPECT in our series was due to the occurrence of hypoperfusion in PISPECT, which was seen in 34.5% of our patients; and (c) hypoperfusion in PISPECT did have localizing value when it occurred on the same side as the hypoperfusion noted in IISPECT. CONCLUSION: On the basis of our findings, we recommend the use of 3 distinct perfusion patterns that emerge from the combined interpretation of IISPECT and PISPECT we proposed earlier (patterns 1-3), for localization purposes when possible, rather than ictal SPECT, IISPECT, or PISPECT by itself.

Ictal asystole--late manifestation of partial epilepsy and importance of cardiac pacemaker.

Ictal asystole (IA) is a life-threatening complication of epilepsy and is a potential mechanism of sudden unexplained death in epilepsy (SUDEP). This entity has been proven by multiple case reports and small case series. The management of the patients with IA is still in early phase of discussion. We report a patient with medically intractable cryptogenic partial epilepsy for 27 years who presented with new onset drop attacks. During the epilepsy monitoring unit stay he was found to have a left fronto-temporal partial onset seizures which triggered brady-arrhythmia followed by asystole for 20s. A cardiac pacemaker was implanted and the patient was followed for 2 years. He continued to have simple and complex partial seizures but did not have drop attacks anymore. He still occasionally feels the activation of his pacemaker during simple partial phase of his seizures but the characteristic loss of muscle tone never happened again which made him highly satisfied. Our case demonstrates that IA can even happen decades after the onset of epilepsy. Cardiac pacemaker should be considered in all patients with IA as it prevents ictal falls and possibly SUDEP.