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Biomedical subjects

Gregory L Barkley

Publications and source records attributed to Gregory L Barkley.

12 recordsLinked to original sources
PubMed2006

Efficacy, safety, and tolerability of oxcarbazepine monotherapy.

OBJECTIVE: This prospective, open-label, multicenter study evaluated the efficacy and tolerability of oxcarbazepine as monotherapy in patients with partial seizures who switched from their current antiepileptic drug (AED) monotherapy because of lack of efficacy or poor tolerability. METHOD: Patients (>or=12 years old) experiencing 2-40 seizures per month while receiving an AED were included. During a 16-week treatment phase, oxcarbazepine was initiated (8-10mg/kg for children; 600 mg/day for adults) and titrated up over 4 weeks while the existing AED was tapered off. Improvement in seizure frequency (defined as >or=50% reduction compared with baseline) was evaluated for all patients, as well as the subgroups of patients switched due to poor tolerability or lack of efficacy. RESULTS: Overall, 52% of patients experienced a 50% reduction in seizure frequency, 35% had a >or=75% reduction, and 18% were seizure-free. The most frequent (>10%) adverse events were dizziness, nausea, headache, somnolence, and fatigue. Overall, 17% of patients prematurely withdrew because of an adverse event; 62% of these withdrawals occurred during the conversion period. CONCLUSION: Oxcarbazepine as monotherapy may be a favorable treatment option for patients with partial seizures or poor tolerability of their existing monotherapy regimen.

Adolescent↗
PubMed2006

Improved quality of life in patients with partial seizures after conversion to oxcarbazepine monotherapy.

OBJECTIVE: Quality of life (QOL) was assessed in patients who switched to oxcarbazepine monotherapy because of the lack of efficacy or poor tolerability of their current antiepileptic drug (AED). METHOD: This open-label, single-arm study consisted of patients aged 12 >or= years with partial onset seizures. Oxcarbazepine (8-10mg/kg/day for children, 600 mg/day for adults) was titrated up over 4 weeks while the existing AED was tapered off. QOL was evaluated at baseline and end of study (Week 16) using the validated-in-epilepsy QOLIE-31 questionnaire. RESULTS: For all patients who completed the QOLIE-31 at baseline and completion, a statistically significant improvement was noted for both the composite and multi-item subscale QOL scores (P<0.05 vs baseline). Statistically significant mean percentage improvements of >or=10% from baseline (range=10.8-50.1%) were also noted. Significant improvements were seen in health-related QOL for patients who experienced seizure freedom or >or=50% reductions in seizure frequency with oxcarbazepine monotherapy. CONCLUSIONS: Patients with partial seizures who switched to oxcarbazepine monotherapy showed statistically significant, clinically relevant improvements in QOL.

Adolescent↗
PubMed2005

Language laterality determined by MEG mapping with MR-FOCUSS.

Magnetoencephalography recordings were made on 27 patients with localization related epilepsy during two different language tasks involving semantic and phonological processing (verb generation and picture naming). These patients underwent the semi-invasive intracarotid amobarbital procedure (IAP), also referred to as the Wada test, to determine the language-dominant hemisphere. Magnetoencephalography (MEG) data were analyzed by MR-FOCUSS, a current density imaging technique. A laterality index (LI) was calculated from this solution to determine which hemisphere had more neural activation during these language tasks. The LIs for three separate latencies, within each language task, were calculated to determine the latency that correlated best with each patient's IAP result. The LI for all language processing was calculated for the interval 150-550 ms, the second LI was calculated for the interval 230-290 ms (Wernicke's activation), and the third LI was calculated for the interval 396-460 ms (Broca's activation). In 23 of 24 epilepsy patients with a successful IAP, the LIs for Broca's activation, during the picture naming task, were in agreement with the results of the IAP (96% agreement). One of three patients who had an undetermined or bilateral IAP had an LI calculated for Broca's activation (396-460 ms) that agreed with intracranial mapping and clinical testing. These results indicate an 89% agreement rate (24 of 27) for magnetoencephalographic LI determination of the hemisphere of language dominance.

Adolescent↗
PubMed2005

Magnetoencephalographic localization of the basal temporal language area.

Magnetoencephalography (MEG) recordings were made on 25 native English-speaking patients with localization-related epilepsy during a semantic language task (verb generation). Eighteen right-handed subjects with normal reading ability had MEG scans performed during the same language task. MEG data was analyzed by MR-FOCUSS, a current density imaging technique. Detectable MEG signals arising from activation in the left fusiform gyrus, also known as the basal temporal language area (BTLA), occurred at 167 +/- 18 ms (n = 43) in all subjects. The BTLA has been associated with a variety of language production and comprehension tasks involving processing of semantic, orthographic, and phonologic information. MEG may become an important tool in efforts to further define the linguistic operations of specific regions within this language area.

Adolescent↗
PubMed2005

Photic- and pattern-induced seizures: expert consensus of the Epilepsy Foundation of America Working Group.

PURPOSE: In August, 2004, the Epilepsy Foundation of America convened a workshop to begin to develop an expert consensus on photosensitive seizures. METHODS: Literature and data were reviewed, and consensus was derived from discussion. RESULTS: A flash is a potential hazard if it has luminance >or=20 cd/m2, occurs at a frequency of >or=3 Hz, and occupies a solid visual angle of >or=0.006 steradians (approximately 10% of the central visual field or 25% of screen area at typical viewing distances). A transition to or from saturated red also is considered a risk. A pattern with the potential for provoking seizures contains clearly discernible stripes, numbering more than five light-dark pairs of stripes in any orientation. When the light-dark stripes of any pattern collectively subtend at the eye from the minimal-expected viewing distance a solid angle of >0.006 steradians, the luminance of the lightest stripe is >50 cd/m2, and the pattern is presented for >or=0.5 s, then the pattern should display no more than five light-dark pairs of stripes, if the stripes change direction, oscillate, flash, or reverse in contrast; if the pattern is unchanging or smoothly drifting in one direction, no more than eight stripes. These principles are easier to apply in the case of fixed media, for example, a prerecorded TV show, which can be analyzed frame-by-frame, as compared with interactive media. CONCLUSIONS: A consensus view of stimuli likely to provoke visually evoked seizures can be developed.

Computer Terminals↗
PubMed2005

Photic- and pattern-induced seizures: a review for the Epilepsy Foundation of America Working Group.

PURPOSE: This report summarizes background material presented to a consensus conference on visually provoked seizures, convened by the Epilepsy Foundation of America. METHODS: A comprehensive review of literature was performed. RESULTS: Photosensitivity, an abnormal EEG response to light or pattern stimulation, occurs in approximately 0.3-3% of the population. The estimated prevalence of seizures from light stimuli is approximately 1 per 10,000, or 1 per 4,000 individuals age 5-24 years. People with epilepsy have a 2-14% chance of having seizures precipitated by light or pattern. In the Pokemon cartoon incident in Japan, 685 children visited a hospital in reaction to red-blue flashes on broadcast television (TV). Only 24% who had a seizure during the cartoon had previously experienced a seizure. Photic or pattern stimulation can provoke seizures in predisposed individuals, but such stimulation is not known to increase the chance of subsequent epilepsy. Intensities of 0.2-1.5 million candlepower are in the range to trigger seizures. Frequencies of 15-25 Hz are most provocative, but the range is 1-65 Hz. Light-dark borders can induce pattern-sensitive seizures, and red color also is a factor. Seizures can be provoked by certain TV shows, movie screen images, video games, natural stimuli (e.g, sun on water), public displays, and many other sources. CONCLUSIONS: Recommendations on reducing risk of seizures have been developed by agencies in the United Kingdom, Japan, and the International Telecommunications Union, affiliated with the United Nations. The Epilepsy Foundation of America has developed a consensus of medical experts and scientists on this subject, reported in an accompanying work.

Cartoons as Topic↗
PubMed2004

Controversies in neurophysiology. MEG is superior to EEG in localization of interictal epileptiform activity: Pro.

UNLABELLED: Both EEG and magnetoencephalography (MEG), with a time resolution of 1 ms or less, provide unique neurophysiologic data not obtainable by other neuroimaging techniques. MEG and EEG have often been compared to each other now although the two are complementary. Now that MEG has emerged as a mature clinical technology, it is worthwhile to compare the relative strengths of each for the localization of interictal epileptiform activity and to describe the strengths of MEG relative to EEG in the localization of interictal epileptiform activity. The sources of MEG and EEG signals will first be reviewed. Issues relevant to solving the forward problem and the inverse problem in MEG and EEG will be addressed followed by a comparison of research concerning the detection and localization of interictal epileptiform activity by MEG and EEG. The emphasis will be upon techniques and software routinely used in clinical applications but some emerging areas of MEG research which are entering clinical practice will also be reviewed. SIGNIFICANCE: MEG is a new noninvasive neurophysiologic technique which provides unique information for the clinical evaluation of patients with epilepsy, revealing aspects of neuronal function that previously could only be obtained by invasive EEG monitoring, and giving a new window for research of neuronal activity.

Cerebral Cortex↗
PubMed2004

Antiepileptic drugs and reduced bone mineral density.

There is a growing interest in recognizing the association between antiepileptic drugs and reduced bone mineral density. Although the literature regarding this association has been available for more than three decades, the management of this complication remains unclear. We review the relevant literature regarding antiepileptic drugs and reduction in bone mineral density with the aim of developing some guidelines for practical management of this problem. This review focuses on the mechanism of antiepileptic drug-induced bone loss, its recognition, and its management.

Absorptiometry, Photon↗
PubMed2003

Magnetoencephalographic validation parameters for clinical evaluation of interictal epileptic activity.

The authors demonstrate that the confidence volume (the spatial volume that encompasses the 95% probability of source localization) of the single equivalent current dipole is helpful in validating magnetoencephalographic epileptic spike mapping. Such mapping involves distinguishing spikes from other neuronal events. The usual criteria for validating dipole fit reliability involve four parameters-correlation coefficient (R > or =0.98), goodness of fit (> or =0.95), root mean square magnetic field value (>400 fT), and dipole moment (Q value > 200 nAm)-but other parameters (direction of dipole moment, location of dipole, and confidence volume) can be considered. In 21 patients with epilepsy, the average correlation coefficient for 608 epileptic spikes was 0.99; average goodness of fit, 0.98; average root mean square, 1,198 fT; and the average Q value, 370 nAm. The mean average confidence volume was 0.30 +/- 0.27 cm3. Correlation coefficient values for quiet brain activity were less than 0.90; goodness of fit values, less than 0.85; and confidence volumes were large (>5 cm3); and for noise runs (no subject) they were even larger (>100 cm3), although correlation coefficient values were more than 0.80 and goodness of fit values were more than 0.85. Confidence volumes for noise data are large-for background brain activity even larger-but confidence volumes for epileptic spikes are small. Confidence volume, in conjunction with other parameters, may be a robust parameter for spike selection.

Algorithms↗
PubMedDate not supplied

MEG and EEG in epilepsy.

Both EEG and magnetoencephalogram (MEG), with a time resolution of 1 ms or less, provide unique neurophysiologic data not obtainable by other neuroimaging techniques. MEG has now emerged as a mature clinical technology. While both EEG and MEG can be performed with more than 100 channels, MEG recordings with 100 to 300 channels are more easily done because of the time needed to apply a large number of EEG electrodes. EEG has the advantage of the long-term video EEG recordings, which facilitates extensive temporal sampling across all periods of the sleep/wake cycle. MEG and EEG seem to complement each other for the detection of interictal epileptiform discharges, because some spikes can be recorded only on MEG but not on EEG and vice versa. Most studies indicate that MEG seems to be more sensitive for neocortical spike sources. Both EEG and MEG source localizations show excellent agreement with invasive electrical recordings, clarify the spatial relationship between the irritative zone and structural lesions, and finally, attribute epileptic activity to lobar subcompartments in temporal lobe and to a lesser extent in extratemporal epilepsies. In temporal lobe epilepsy, EEG and MEG can differentiate between patients with mesial, lateral, and diffuse seizure onsets. MEG selectively detects tangential sources. EEG measures both radial and tangential activity, although the radial components dominate the EEG signals at the scalp. Thus, while EEG provides more comprehensive information, it is more complicated to model due to considerable influences of the shape and conductivity of the volume conductor. Dipole localization techniques favor MEG due to the higher accuracy of MEG source localization compared to EEG when using the standard spherical head shape model. However, if special care is taken to address the above issues and enhance the EEG, the localization accuracy of EEG and MEG actually are comparable, although these surface EEG analytic techniques are not typically approved for clinical use in the United States. MEG dipole analysis is approved for clinical use and thus gives information that otherwise usually requires invasive intracranial EEG monitoring. There are only a few dozen whole head MEG units in operation in the world. While EEG is available in every hospital, specialized EEG laboratories capable of source localization techniques are nearly as scarce as MEG facilities. The combined use of whole-head MEG systems and multichannel EEG in conjunction with advanced source modeling techniques is an area of active development and will allow a better noninvasive characterization of the irritative zone in presurgical epilepsy evaluation. Finally, additional information on epilepsy may be gathered by either MEG or EEG analysis of data beyond the usual bandwidths used in clinical practice, namely by analysis of activity at high frequencies and near-DC activity.

Brain↗