Visual versus computer evaluation of thiopental-induced EEG changes in temporal lobe epilepsy

Anesthetic management of the patient with epilepsy or prior seizures

PURPOSE OF REVIEW

Epilepsy is a clinical disorder of paroxysmal recurring seizures, the diagnosis excluding alcohol or drug withdrawal seizures or such recurring exogenous events as repeated insulin-induced hypoglycemia. Epilepsy has a profound impact on each individual diagnosed with this disease.

RECENT FINDINGS

New antiepileptic drugs (AEDs) have been a major change in the approach to management of patients with epilepsy. These drugs tend to have fewer significant drug interactions and less severe side effects. Nonetheless, first-generation AEDs are still widely used. Propofol and desflurane have reliable anticonvulsant effects, whereas remifentanil in larger doses and sevoflurane appear to support epileptiform activity, although the clinical significance of these observations is unclear.

SUMMARY

The primary concerns for providing anesthesia to the patient with epilepsy are the capacity of anesthetics to modulate or potentiate seizure activity and the interaction of anesthetic drugs with AEDs. Proconvulsant and anticonvulsant properties have been reported for virtually every anesthetic such that these properties become elements of the anesthetic plan in the patient with epilepsy. Moreover, AEDs have many physiologic and pharmacologic effects that can have an impact on an anesthetic.

Effects of intravenous mannitol on EEG recordings in stroke patients

OBJECTIVES

To evaluate the usefulness of continuous EEG monitoring of stroke patients during and after intravenously infused mannitol.

METHODS

Patients were rapidly administered 50 g of intravenous mannitol solution with continuous EEG monitoring for 3h pre- and post-drug infusion in the neurological intensive care unit. Visual and spectral analyses of EEG recording pre- and post-mannitol infusion were carried out.

RESULTS

The study consisted of 47 patients. Of 38 patients with intracranial hemorrhage, 33 had abnormal EEG findings pre-mannitol administration. After mannitol therapy, visual analysis of the drug-induced EEG changes showed that the EEG findings were unchanged in 13 patients, demonstratively improved in 22 patients, and worse in 3 patients. The spectral analysis demonstrated that mannitol-induced EEG changes increased in alpha power and decreased in delta power in the lesion hemispheres, especially in the central and middle temporal areas. Maximal effects occurred 30 min post-mannitol infusion, and remained significant for 2h post-infusion. Of the 9 patients with cerebral infarction, only one with diffuse background slowing of one-side dominance pre-mannitol improved after the infusion of mannitol.

CONCLUSIONS

The results of our investigation indicated that continuous EEG monitoring of mannitol treatment can reflect the brain edema, raised ICP in stroke patients, and provide assessment the drugs effects of antiedema and intracranial pressure lowering in vivo.

Sleep spindle asymmetry in epileptic patients

OBJECTIVE

To investigate sleep spindle asymmetry in patients with idiopathic generalized epilepsy (IGE), cryptogenic partial epilepsy (CPE), and symptomatic partial epilepsy (SPE).

METHODS

Post-sleep deprivation EEG records of the patients were investigated. Fast Fourier transform was applied to 200 s of stage-2 activity (without spikes, spike-waves and artefacts). Individual spindle frequency and topography was identified in each patient. Spindle intensity was computed and expressed in microvolts. In order to calculate spindle asymmetry the site of maximum spindle intensity within one hemisphere was compared to the mirror site in the other hemisphere. Asymmetry was expressed by the asymmetry index (AI). In the PE group AI was defined as [AI=(P-N)/(P+N)x100], where P and N were spindle intensity in the pathological and normal hemisphere, respectively. In the IGE group P and N were substituted for L and R (spindle intensity in the left and right hemisphere, respectively).

RESULTS

In IGE patients spindle asymmetry was in the range of -13 to +12%. No significant lateralization to the left or right hemisphere was observed. In PE patients, spindle asymmetry ranged from -23 to+29%. As compared to spindle intensity in the unaffected hemisphere, spindling was enhanced in the 'epileptic' hemisphere in most PE patients (15/20 in the CPE and 5/7 in the SPE group).

CONCLUSION

In IGEs (where the epileptic condition involved both hemispheres to the same extent) spindle intensity did not show significant asymmetry. In PE patients (where the epileptic process was clearly lateralized to one hemisphere while the other hemisphere was unaffected) enhanced spindling usually was related to the side of the epileptic process. The generally held notion that the pathological hemisphere displays less spindling than the healthy one might be misleading in cases of focal epilepsy. The results suggest that epileptogenic cortex slightly facilitates spindle generation.

Quantitative EEG analysis in clinical settings

Quantitative EEG techniques are becoming more available. Eventually, all EEG will be digital. Various digital utility programs can help even now with storage and viewing the polygraph EEG itself. Techniques of frequency analysis, topographic mapping and discriminant functions are also available but have limited clinical use. Applications as a monitoring tool and careful analysis of epileptic spikes have been shown some promise but need further study to identify their proper clinical roles.

Status of quantitative EEG (QEEG) in clinical practice, 1994

Clinical quantitative EEG (qEEG) is a complex specialty that may include not only standard EEG but also digital ("paperless") EEG, topographic mapping, spectral analysis, spectral coherence, long latency and event related potentials (EP), significance probability mapping (SPM), dipole source localization methodology (DLM), and discriminant function analysis. There are three basic clinical uses: non-specific detection of organicity/encephalopathy, specific categorization of disease or clinical condition, and epileptic source localization. Extreme variations exist in the competency of laboratories practicing clinical qEEG; universally agreed upon standards of practice have not been established but there are a number of efforts to do so. As expected, the clinical value of qEEG to patients varies similarly. Criticisms of qEEG have now been answered: Color displays need not be deceptive. Statistical "capitalization upon chance" can be easily avoided. By training and with newer analytic procedures, artifacts can be recognized and often removed. Data based upon spectral analysis and EP can reliably classify clinical conditions thereby demonstrating a greater sensitivity to EEG/EP data than possible by conventional visual inspection. QEEG is clearly of clinical value when performed in concert with standard EEG and analyzed by clinicians with demonstrated competency in standard EEG followed by specialized training and demonstrated competency in qEEG. QEEG is not a simple substitute for conventional EEG and cannot be seen as a substitute for clinical competence. Although continuing to develop, qEEG technology has matured sufficiently and is now well established. Concerns regarding its clinical use have primarily resulted from its misapplication and misinterpretation stemming, largely, from inadequate personnel training and expertise.

Effect of barbiturate on epileptiform activity: comparison between intravenous and oral administration. Sphenoidal, zygomatic and temporal recordings

The present study was performed in order to compare: 1) the differences between oral and intravenous barbiturate on interictal epileptiform activity (sharp-waves and spikes) in the EEG, and 2) interictal epileptiform activity in the sphenoidal electrode compared to the temporal and zygomatic electrodes (an electrode placed at the cutaneous entry of the sphenoidal electrode) during intravenous barbiturate administration in patients with epilepsy. Two procedures were performed: 1) an oral pentobarbital sleep induction with 10-20 electrode placement including a zygomatic electrode, and 2) an intravenous thiopental sleep induction with the same electrode placement including a sphenoidal electrode. Thirty eight patients with complex partial seizures were included. During the oral pentobarbital procedure 34 of 38 (90%) patients showed interictal epileptiform activity compared with 22 of 38 (55%) patients during the intravenous thiopental procedure (p < 0.005). A interictal epileptiform focus was observed in 33 (87%) patients in the oral procedure and in 19 (50%) patients in the intravenous procedure (p < 0.01). Interictal epileptiform activity recorded in the sphenoidal electrode was also recorded in the zygomatic electrode. Except from two patients a good correlation was observed between the zygomatic electrodes and the F7/F8 electrodes. We conclude that administration of intravenous thiopental offers no advantage compared to the administration of oral pentobarbital as an activating procedure, and for standard interictal EEG recordings with sleep activation procedures, suitable places scalp electrodes including a zygomatic electrode with the use of oral pentobarbital may be sufficient.

Lateralization of the epileptogenic focus by computerized EEG study and neuropsychological evaluation

The localization of the epileptogenic focus relies on different factors. In patients with partial seizures, asymmetries in EEG background activity were measured by a statistical evaluation of spectral data. Neurophysiological results were compared with neuropsychological findings and MRI. Fifteen of 22 patients showed asymmetries in EEG background activity. The most prominent abnormality was a statistically significant increase of slow activity observed in 59% of cases. Delta asymmetry coincided with the site of lesions, evidenced by MRI, in 83% of patients; with the site of decreased beta activity in 60% and with the maximum level of spiking activity in 58% of cases. Neuropsychological tests showed a lateralization of the hemispheric function which coincided with delta asymmetry in 33% of patients. These results suggest that the EEG background activity, when compared with other parameters, may represent a useful method in lateralizing the epileptogenic focus.

Quantitative comparison of cell loss and thiopental-induced EEG changes in human epileptic hippocampus

Thiopental-induced EEG beta activity recorded from mesial and lateral temporal lobe sites was analyzed both visually and by computer in 30 patients with complex partial seizures. All patients later received anterior temporal lobectomy. Volumetric cell densities and percentage of principal cell loss relative to normal controls were determined in several different areas of each resected temporal lobe. The percentage of drug-induced beta activity was then compared with the percentage of cell loss by (a) making precise topographic correlations between induced beta and cell loss, (b) relating the overall degree of left/right beta asymmetry to cell loss averaged over wide regions, and (c) comparing the likelihood of left/right beta asymmetries in patients with and without extreme cell loss. The results obtained were consistently negative and were unaffected by whether EEG data were analyzed by computer or visual inspection. These results indicate that the well-known loss of drug-induced beta activity found in epileptogenic regions is not an indicator of the degree of cell loss or sclerosis. The underlying focal dysfunction measured by EEG beta activity remains unknown, and factors such as focal hypoperfusion, hypometabolism, and the microanatomic features of the cells remaining in the focus should be investigated.

Computer enhancement of scalp-sphenoidal ictal EEG in patients with complex partial seizures

Color topographic maps of scalp/sphenoidal ictal EEG records were computer-generated in 5 patients with medically refractory complex partial seizures of suspected temporal lobe origin. Seven ictal EEG records were analyzed by parsing them into a series of 1.28 sec epochs. User-interactive, computer techniques were utilized to replace eye movement and other artifactual segments in the peri-ictal records with nearby uncontaminated EEG segments. Artifact replacement techniques were designed to minimize or eliminate EEG discontinuities in those epochs in which artifact was removed. Significance probability maps consisting of z scores were constructed by comparing theta band power for each 1.28 sec epoch composing the peri-ictal period with the mean and standard deviation of theta power computed from a pre-ictal baseline period consisting of 50-75 epochs. The resulting maps were compared with available independent clinical measures in order to validate their usefulness. The independent measures consisted of non-invasive data (visual impressions of raw scalp/sphenoidal ictal EEGs and positron emission tomography) and invasive data (depth ictal recordings, pathological findings in resected temporal lobes, and surgical outcome). Ictal topographic maps appeared to either confirm or provide new localizing information in all 5 patients. In 3 of 5 patients, several seconds of localized theta suppression preceded localized theta augmentation during the peri-ictal period. The transition between the 2 states was very rapid (approximately 2 sec). The spatial locus of suppression was always in agreement with the spatial locus of augmentation. In general, the maps were considerably easier to interpret than the raw scalp/sphenoidal ictal EEGs: (1) Localized theta suppression in the maps was not evident from visual inspection of the raw ictal scalp/sphenoidal EEG. (2) Clear localized theta augmentation in the maps occurred well before the appearance of unambiguous phase reversals in the raw scalp/sphenoidal ictal EEG. (3) Mapping data were correctly lateralizing in 1 patient in whom visual interpretation of the raw scalp/sphenoidal ictal EEGs was considered non-localizing but often suggestive of a seizure origin in the hemisphere contralateral to that implicated by depth recordings, PET, and pathological data. These results suggest that topographic mapping of scalp/sphenoidal ictal EEGs in patients with complex partial seizures may eventually prove to be a useful adjunct to the interpretation of raw ictal recordings.

Frequency analysis and topographic mapping of EEG and evoked potentials in epilepsy

Frequency analysis (spectral analysis) of both EEG and evoked potentials were studied prospectively in 52 patients with complex partial seizures to see if such tests could help localize the epileptic focus. Results were examined in line, bar and topographic head display formats. Asymmetries of fast and slow frequency components were identified in 26/52 patients. The existence and localization of such frequency alterations agreed with the overall results of other tests including the routine EEG, ictal EEG records, thiopental-activated EEG, CT or MRI, positron computed tomography (PET), and neuropsychometric testing. Changes were present in all 5 temporal lobe epilepsy cases that had a focal CT or MRI change, and in a majority (17/33) of cases in which the baseline EEG showed no focal slowing. These changes agreed with the preponderance of evidence in lateralizing the epileptic focus. Overall, EEG and evoked potential frequency analysis and topographic mapping do appear to offer data which are useful and complementary to other available test results, especially when a suspected lesion does not already show up as a defect on the CT scan or as a well-defined EEG slow focus. Considerable care needs to be taken to identify artifacts and normal EEG variants when interpreting these tests.