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P Boon

Publications and source records attributed to P Boon.

At least 19 recordsLinked to original sources
PubMed2001

Anticipation of epileptic seizures from standard EEG recordings.

BACKGROUND: New methods derived from non-linear analysis of intracranial recordings permit the anticipation of an epileptic seizure several minutes before the seizure. Nevertheless, anticipation of seizures based on standard scalp electroencephalographical (EEG) signals has not been reported yet. The accessibility to preictal changes from standard EEGs is essential for expanding the clinical applicability of these methods. METHODS: We analysed 26 scalp-EEG/video recordings, from 60 min before a seizure, in 23 patients with temporal-lobe epilepsy. For five patients, simultaneous scalp and intracranial EEG recordings were assessed. Long-term changes before seizure onset were identified by a measure of non-linear similarity, which is very robust in spite of large artifacts and runs in real-time. FINDINGS: In 25 of 26 recordings, measurement of non-linear changes in EEG signals allowed the anticipation of a seizure several minutes before it occurred (mean 7 min). These preictal changes in the scalp EEG correspond well with concurrent changes in depth recordings. INTERPRETATION: Scalp-EEG recordings retain sufficient dynamical information which can be used for the analysis of preictal changes leading to seizures. Seizure anticipation strategies in real-time can now be envisaged for diverse clinical applications, such as devices for patient warning, for efficacy of ictal-single photon emission computed tomography procedures, and eventual treatment interventions for preventing seizures.

Electroencephalography↗
PubMed2001

Day length has a major effect on the response of protein synthesis rates to feeding in growing Japanese quail.

We investigated the effect of day length on mixed protein fractional synthesis rates (K(S)) in 14- and 21-d-old Japanese quail (Coturnix c. japonica) habituated to either a long day length, 18 h light/6 h dark (LDL), or short day length, 6 h light/18 h dark (SDL), with free access to food during the light period. Rates of protein synthesis were measured by a flooding dose of L-[1-(13)C]leucine. In both groups, we measured K(S) of pectoral muscle, liver and heart after an overnight period of food deprivation and after 2-h food access at dawn. Rates of protein synthesis were also measured in LDL quail starved for 18 h and refed for 2 h. SDL chicks were smaller and had lower tissue weights at 2 wk of age than did LDL chicks (P<0.05). Starvation led to a lower rate of protein synthesis in those animals starved for 18 h. Food availability after starvation for 18 h induced a significant rise in tissue protein synthesis in both SDL and LDL quail (P<0.05). This increase was absent in LDL quail after a 6-h starvation period. There was an increase in K(S) to ad hoc changes in food supply. By determining the daily period in which feeding can occur, day length has a major effect on protein synthesis rates. This effect will determine the overall growth chicks are able to achieve that have been subjected to different day lengths.

Animals↗
PubMed2000

Cobalt-55 positron emission tomography in late-onset epileptic seizures after thrombo-embolic middle cerebral artery infarction.

The pathogenesis of late-onset epileptic seizures after thrombo-embolic cerebral infarction is poorly understood. Our previous positron emission tomographic (PET) studies with 15O have demonstrated that post-apoplectic epilepsy is associated with more severe brain ischemia, but we were unable to determine if this was the cause or the consequence of the seizures. Using cobalt-55 (55Co) as PET tracer we can now distinguish recurrent, recent infarction in patients with a previous old infarct in the same vascular territory. In seven out of twelve patients with post-apoplectic seizures an increased uptake of 55Co was observed in the border area and in two of them also within the old infarct core. In the control group, composed of eight seizure-free patients with also an old infarct involving the cortical territory of the middle cerebral artery, no increase in 55Co uptake was observed on PET examination. The present study indicates that in a significant number of patients late-onset epilepsy is the clinical expression of recurrent strokes, occurring in the same vascular territory.

Aged↗
PubMed2000

Dipole location errors in electroencephalogram source analysis due to volume conductor model errors.

An examination is made of dipole location errors in electroencephalogram (EEG) source analysis, due to not incorporating the ventricular system (VS), omitting a hole in the skull and underestimating skull conductivity. The simulations are performed for a large number of test dipoles in 3D using the finite difference method. The maximum dipole location error encountered, utilising 27 and 53 electrodes is 7.6 mm and 6.1 mm, respectively when omitting the VS, 5.6 mm and 5.2 mm, respectively when neglecting the hole in the skull, and 33.4 mm and 28.0 mm, respectively when underestimating skull conductivity. The largest location errors due to neglecting the VS can be found in the vicinity of the VS. The largest location errors due to omitting a hole can be found in the vicinity of the hole. At these positions the fitted dipoles are found close to the hole. When skull conductivity is underestimated, the dipole is fitted close to the skull-brain border in a radial direction for all test dipoles. It was found that the location errors due to underestimating skull conductivity are typically higher than those found due to neglecting the VS or neglecting a hole in the skull.

Electric Conductivity↗
PubMed2000

Influence of measurement noise and electrode mislocalisation on EEG dipole-source localisation.

Measurement noise in the electro-encephalogram (EEG) and inaccurate information about the locations of the EEG electrodes on the head induce localisation errors in the results of EEG dipole source analysis. These errors are studied by performing dipole source localisation for simulated electrode potentials in a spherical head model, for a range of different dipole locations and for two different numbers (27 and 148) of electrodes. Dipole source localisation is performed by iteratively minimising the residual energy (RE), using the simplex algorithm. The ratio of the dipole localisation error (cm) to the noise level (%) of Gaussian measurement noise amounts to 0.15 cm/% and 0.047 cm/% for the 27 and 148 electrode configurations, respectively, for a radial dipole with 40% eccentricity The localisation error due to noise can be reduced by taking into account multiple time instants of the measured potentials. In the case of random displacements of the EEG electrodes, the ratio of dipole localisation errors to electrode location errors amounts to 0.78 cm-1 cm and 0.27 cm-1 cm for the 27 and 148 electrode configurations, respectively. It is concluded that it is important to reduce the measurement noise, and particularly the electrode mislocalisation, as the influence of the latter is not reduced by taking into account multiple time instants.

Electricity↗
PubMed2000

Automatic localization of EEG electrode markers within 3D MR data.

The electrical activity of the brain can be monitored using ElectroEncephaloGraphy (EEG). From the positions of the EEG electrodes, it is possible to localize focal brain activity. Thereby, the accuracy of the localization strongly depends on the accuracy with which the positions of the electrodes can be determined. In this work, we present an automatic, simple, and accurate scheme that detects EEG electrode markers from 3D MR data of the human head.

Electrodes↗
PubMed2000

EEG dipole source localization using artificial neural networks.

Localization of focal electrical activity in the brain using dipole source analysis of the electroencephalogram (EEG), is usually performed by iteratively determining the location and orientation of the dipole source, until optimal correspondence is reached between the dipole source and the measured potential distribution on the head. In this paper, we investigate the use of feed-forward layered artificial neural networks (ANNs) to replace the iterative localization procedure, in order to decrease the calculation time. The localization accuracy of the ANN approach is studied within spherical and realistic head models. Additionally, we investigate the robustness of both the iterative and the ANN approach by observing the influence on the localization error of both noise in the scalp potentials and scalp electrode mislocalizations. Finally, after choosing the ANN structure and size that provides a good trade off between low localization errors and short computation times, we compare the calculation times involved with both the iterative and ANN methods. An average localization error of about 3.5 mm is obtained for both spherical and realistic head models. Moreover, the ANN localization approach appears to be robust to noise and electrode mislocations. In comparison with the iterative localization, the ANN provides a major speed-up of dipole source localization. We conclude that an artificial neural network is a very suitable alternative for iterative dipole source localization in applications where large numbers of dipole localizations have to be performed, provided that an increase of the localization errors by a few millimetres is acceptable.

Brain↗
PubMed2000

The value of the number-needed-to-treat method in antiepileptic drug trials.

PURPOSE: There is controversy between clinicians and statisticians on the appropriateness of the number needed to treat (NNT) as a summary statistic to report the effectiveness of a treatment. We examine the two viewpoints and make proposals concerning the reporting of clinical trial results. METHODS: In the context of antiepileptic treatments, we explain the two different viewpoints and illustrate the use of the odds ratio, relative risk, absolute difference, and NNT on the results of randomized clinical trials with topiramate (TPM). Special attention is paid to the use of these summary statistics in meta-analyses. Here, the NNT is the expected number of patients one would need to treat to achieve a single occurrence of a specified good outcome (e.g., 50% reduction in seizure rate) in comparison to no (or placebo) treatment. RESULTS: Although the NNT is readily interpretable in some instances, it exhibits undesirable statistical behavior in other cases. In particular, confidence intervals for the NNT may split into two intervals and extend to positive and negative infinity when treatment efficacy is not clearly established by the data. Meta-analyses cannot be sensibly conducted directly on the NNT scale. CONCLUSIONS: Although other measures, such as the odds ratio, have been more commonly used in the context of meta-analyses, clinicians prefer the NNT because it gives them a clearer clinical interpretation of the effectiveness of a (new) treatment. On the other hand, statisticians do not recognize the value of the NNT, as it has undesirable statistical properties. Some reconciliation between the two views could be achieved when the clinicians acknowledge the weak aspects of the NNT and when statisticians realize that statistical appropriateness is not the same as clinical relevance. It is suggested that the NNT be used as a secondary reporting tool not on an equal footing with the classic scales.

Anticonvulsants↗
PubMed2000

Acute single photon emission computed tomographic study of vagus nerve stimulation in refractory epilepsy.

PURPOSE: Left-sided vagus nerve stimulation (VNS) is an efficacious treatment for patients with refractory epilepsy. The precise mechanism of action remains to be elucidated. Only limited data on VNS-induced changes in regional cerebral blood flow (rCBF) are available. The aim of this study was to investigate rCBF changes during initial VNS with single-photon emission computed tomography (SPECT). METHODS: In 12 patients (8 women, 4 men) with mean age of 32 years and mean duration of epilepsy of 19 years, VNS-induced rCBF changes were studied by means of a 99mTc-ethyl cysteinate dimer activation study with a single-day split-dose protocol before and immediately after initial stimulation. Images were acquired on a triple-head camera with fan-beam collimators and were reconstructed with scatter and attenuation correction. After coregistration to a standardized template, both a semiquantitative analysis using predefined volumes-of-interest (VOIs) as well as voxel-by-voxel analysis of the intrasubject activation were performed. During follow-up, efficacy of VNS in terms of seizure-frequency reduction was studied. RESULTS: The semiquantitative analysis, with reference to the total counts in all VOIs, revealed a significant decrease of activity in the left thalamus immediately after the initial stimulation train. These results agreed with voxel-by-voxel analysis. In our study ipsilateral thalamic hypoperfusion was the most significant finding. Mean frequency of complex partial seizures was reduced from 30 per month before implantation to six per month after implantation. CONCLUSIONS: VNS induces rCBF changes immediately after initial stimulation that can be studied with SPECT. VNS-induced changes in the thalamus may play an important role in suppression of seizures. However, no significant relation between the level of hypoperfusion and subsequent clinical efficacy was found.

Adolescent↗
PubMed2000

Cost minimization analysis of antiepileptic drugs in newly diagnosed epilepsy in 12 European countries.

A recent United Kingdom cost minimization analysis (CMA) of four antiepileptic drugs (AEDs) used to treat newly diagnosed adult epilepsy demonstrated that a new drug, lamotrigine (LTG), incurred higher costs than carbamazepine (CBZ), phenytoin (PHT), and valproate (VPA), whose costs were similar. This analysis took account of each drug's side-effect and tolerability profile. The present analysis investigated the costs of treatment with LTG, CBZ, PHT, and VPA in 12 European countries. Data were derived from published sources and from a panel of locally based experts. When no published data were available, estimates were obtained using expert opinion by a consensus method. These data were incorporated into a treatment pathway model, which considered the treatment of patients during the first 12 months after diagnosis. The primary outcome considered was seizure freedom. Randomized controlled trials demonstrate that the drugs considered are equally effective in terms of their ability to achieve seizure freedom, and thus the most appropriate form of economic evaluation is a CMA. These trials provided data on the incidence of side effects, dosages, and retention rates. The economic perspective taken was that of society as a whole and the analysis was calculated on an "intent-to-treat" basis. Only direct medical costs were considered. In each country considered, LTG was twofold to threefold more expensive than the other drugs considered. A sensitivity analysis demonstrated that varying each of the assumptions (range defined by expert panels) did not significantly alter the results obtained.

Anticonvulsants↗
PubMed2000

Vagus nerve stimulation in refractory epilepsy: SPECT activation study.

UNLABELLED: Left-sided vagus nerve stimulation (VNS) is an efficacious treatment for patients with refractory epilepsy. The exact mechanism of action remains to be elucidated. This study investigated the acute effects of initial VNS in patients with refractory complex partial epilepsy with or without secondary generalization (complex partial seizures [CPS] +/- SG) by means of a perfusion activation study with SPECT. METHODS: Twelve patients (mean age, 32.2 +/- 10.2 y; age range, 12-47 y) with a mean duration of CPS +/- SG of 19.8 +/- 10.0 y (range, 5-33 y) received VNS. All patients were considered unsuitable candidates for resective surgery because of nonlocalizing findings on presurgical evaluation. VNS efficacy was evaluated for patients with at least 4-mo follow-up. VNS-induced regional cerebral blood flow alterations were studied by a (99m)Tc-ethyl cysteinate dimer activation study with a single-day split-dose protocol before and immediately after an initial stimulation. Images were acquired on a triple-head camera with fanbeam collimators. After coregistration to a standardized template, both a semiquantitative analysis using predefined volumes of interest and a voxel-by-voxel analysis of the intrasubject activation (statistical parametric mapping) were performed. RESULTS: Seizure-frequency changes ranged from 100% decrease to 0% after VNS. The semiquantitative analysis revealed a consistent decrease of activity in the left thalamus (ratio stimulator on/off = 0.94 +/- 0.04; P = 0.005). These results were concordant with the voxel-by-voxel analysis in which a significant deactivation in the left thalamus was found with spread to the ipsilateral hippocampus. There was no statistically significant correlation between initial VNS-induced thalamic hypoperfusion and seizure reduction at maximum follow-up. CONCLUSION: Our findings are consistent with the hypothesis that acute VNS reduces seizure onset or propagation through inhibition of the thalamic relay center. Differences with limited H2(15)O PET data may be associated with temporal effects caused by a stimulation-induced local hemodynamic response and need further investigation. SPECT allows study of cerebral physiopathologic effects of vagus nerve electrostimulation in complex partial epilepsy.

Adolescent↗
PubMed1999

Association of ipsilateral motor automatisms and contralateral dystonic posturing: a clinical feature differentiating medial from neocortical temporal lobe epilepsy.

BACKGROUND: Clinical features that may help to differentiate medial temporal lobe epilepsy (MTLE) from neocortical temporal lobe epilepsy (NTLE) are lacking. OBJECTIVE: To investigate the localizing and lateralizing value of the association of ipsilateral motor automatisms and contralateral dystonic posturing in patients with medically refractory temporal lobe epilepsy. PATIENTS AND METHODS: Videotapes of 60 patients with well-defined MTLE, NTLE, or both were reviewed to assess the presence and the localizing value of unilateral dystonic posturing associated with motor automatisms. RESULTS: Twenty-eight of the 60 patients exhibited unilateral dystonic posturing. This sign was observed in patients with MTLE and NTLE. It was mostly contralateral to the seizure focus in patients with MTLE and exclusively ipsilateral in patients with NTLE. Unilateral motor automatisms occurred in 26 of the 60 patients with MTLE or NTLE. It was predominantly ipsilateral to the seizure focus in patients with MTLE and exclusively contralateral in patients with NTLE. The association of ipsilateral motor automatisms and contralateral dystonic posturing was found in 14 patients with MTLE but in none of the patients with NTLE. Two patients who had medial and neocortical seizure onset also exhibited this clinical feature. This association was not significantly correlated with the postoperative outcome in patients with MTLE. CONCLUSIONS: The association of ipsilateral motor automatisms and contralateral dystonic posturing may help to differentiate MTLE from NTLE with a reliable lateralizing value. This clinical association may reflect a specific pattern in the spread of the ictal discharge.

Adult↗
PubMed1999

Vagus nerve stimulation for medically refractory epilepsy; efficacy and cost-benefit analysis.

INTRODUCTION: Vagus nerve stimulation is a novel treatment for patients with medically refractory epilepsy, who are not candidates for conventional epilepsy surgery, or who have had such surgery without optimal outcome. To date only studies with relatively short follow-up are available. In these studies efficacy increased with time and reached a maximum after a period of 6 to 12 months. Implantation of a vagus nerve stimulator requires an important financial investment but a cost-benefit analysis has not been published. PATIENTS AND METHODS: Our own experience with VNS in Gent comprises 15 patients with mean age of 29 years (range: 17-44 years) and mean duration of epilepsy of 18 years (range: 4-32 years). All patients underwent a comprehensive presurgical evaluation and were found not to be suitable candidates for resective epilepsy surgery. Mean post-implantation follow-up is 24 months (range: 7-43 months). In patients with follow-up of at least one year, efficacy of treatment in terms of seizure control and seizure severity was assessed one year before and after the implantation of a vagus nerve stimulator. Epilepsy-related direct medical costs (ERDMC) before and after the implantation were also compared. RESULTS: A mean reduction of seizure frequency from 14 seizures/month (range: 2-40/month) to 8 seizures/month (range: 0-30/month) was achieved (Wilcoxon signed rank test n = 14; p = 0.0016). Five patients showed a marked seizure reduction of > or = 50%; 6 became free of complex partial seizures, 3 of whom became entirely seizure free for more than 12 months; 2 patients had a worthwhile reduction of seizure frequency between 30-50%; in 2 patients seizure frequency reduction has remained practically unchanged. Seizure freedom or > or = 50% seizure reduction was achieved within the first 4 months after implantation in 6/11 patients. Before the implantation, the mean yearly epilepsy-related direct medical costs per patient were estimated to be 8830 US$ (n = 13; range: 1879-31,129 US$; sd = 7667); the average number of hospital admission days per year was 21 (range: 4-100; sd = 25.7). In the 12 months after implantation, ERDMC had decreased to 4215 US$ (range: 615-11,794 US$; sd = 3558) (Wilcoxon signed rank test n = 13; p = 0.018) and the average number of admission days to 8 (range: 0-35) (Wilcoxon signed rank test n = 13; p = 0.023). CONCLUSION: VNS is an effective treatment of refractory epilepsy and remains effective during long-term follow-up. Cost-benefit analysis suggests that the cost of VNS is saved within two years following implantation.

Adolescent↗
PubMed1999

Long-term results of vagus nerve stimulation in refractory epilepsy.

Vagus nerve stimulation (VNS) is an adjunctive antiepileptic treatment for patients with refractory epilepsy. Limited information on long-term treatment with VNS is available. The purpose of this paper is to present our experience with VNS with a follow-up of up to 4 years. Twenty-five patients (13 females and 12 males) with refractory partial epilepsy were treated with VNS. The first 15 patients with a mean age of 30 years and a mean duration of epilepsy of 17.5 years have sufficient follow-up for analysis. Mean post-implantation follow-up was 29 months and mean stimulation output 2.25 mA. There was a mean seizure frequency reduction from 14 complex partial seizures (CPS) per month before implantation to 8 CPS per month after implantation (P = 0.0016; Wilcoxon signed-rank rest (WSRT)). The mean maximum CPS-free interval changed from 9 to 312 days (P = 0.0007; WSRT). Six patients were free of CPS for at least one year. In one patient, one antiepileptic drug (AED) was tapered; in 10 patients, AEDs remained unchanged; in four, one adjunctive AED was administered. Side effects occurred in six patients, three of whom required a temporary reduction of output current. Nine patients reported no side effects at all. Treatment with VNS remains effective in the long-term. In this series 4 / 15 (27%) patients with highly refractory epilepsy experienced entirely seizure-free intervals of 12 months or more.

Adolescent↗
PubMed1999

[Methyl-11C]thymidine positron emission tomography in tumoral and non-tumoral cerebral lesions.

BACKGROUND: No ideal radiopharmaceutical exists for positron emission tomography (PET) that fulfills all clinical requirements for the study of brain tumors. PURPOSE: The usefulness of a recently developed PET tracer, [methyl-11C]thymidine ([methyl-11C]TdR) is explored in brain tumors. PATIENTS AND METHODS: Twenty patients with confirmed tumoral and non-tumoral brain lesions were investigated with [methyl-11C] TdR PET. The 11C activity was visually and quantitatively assessed. In two patients, dynamic scans were performed. The PET findings were compared to those of magnetic resonance imaging (MRI) or computed tomography (CT) of the brain and to the final diagnosis. RESULTS: Eight out of ten patients with confirmed tumoral lesions or tumor recurrence had increased 11C activity within the lesion. In ten non-tumoral lesions no increased 11C uptake was found. The dynamic PET studies showed that [methyl-11C] TdR first acts as a blood flow tracer, but that later on the uptake of 11C activity is due to labeled metabolites, crossing the blood-brain barrier. Increased tracer activity was only observed in tumoral and not in non-tumoral contrast-enhanced lesions on MRI or CT. CONCLUSIONS: [Methyl-11C] TdR is not a selective PET radiopharmaceutical for brain tumors, but can be used as a tracer for tumoral blood-brain barrier disruption.

Adolescent↗
PubMed1999

Source localization in refractory partial epilepsy.

In this paper, 51 patients with refractory complex partial seizures (CPS) and intracranial structural abnormalities demonstrated with optimum MR (space-occupying: n = 16; atrophic: n = 32; dysplastic: n = 3) were studied. Video-EEG monitoring showed CPS in all patients. In 13 patients, additional intracranial EEG monitoring demonstrated hippocampal seizure onset in 12 and medial occipital ictal onset in 1 patient. Interictal and ictal dipole modeling using a spherical head model and realistic electrode coordinates were performed. Spatiotemporal dipole mapping of interictal epileptic discharges revealed two distinct dipole patterns. Patients with lesions located in the medial temporal lobe (n = 41) and medial occipital lobe (n = 2) uniformly presented a dipole with an elevation of more than 15 degrees relative to the axial plane. Eight out of ten patients with extratemporal lesions and 1 patient with a pure neocortical temporal lesion had a less stable dipole with an elevation less than 15 degrees relative to the axial plane. Dipole modeling of epochs of early ictal discharges revealed a striking correspondence with the interictal findings in individual patients. Ictal dipole modeling identified the ictal onset zone correctly when compared with intracranial EEG recordings from bilateral hippocampal depth electrodes in patients with medial temporal seizure onset. Mapping of dipoles on MR images of individual patients facilitated clinical interpretation of the EEG data. Interictal and ictal dipole mapping provided additional and clinically relevant information and may obviate the need for intracranial EEG studies in some surgical candidates for refractory CPS.

Adolescent↗