Dipole tracing in childhood epilepsy with special reference to rolandic epilepsy

Predictors of one-year language and seizure outcomes in children with epileptic encephalopathy with continuous spike-and-wave during sleep (CSWS)

PURPOSE

Epileptic encephalopathy with continuous spike-and-wave during sleep (CSWS), with its associated impact on language, is an important cause of morbidity with epilepsy in children. The effects of various treatment-approaches and the aetiological/electrophysiological factors affecting therapeutic response are not fully understood.

METHOD

A retrospective study of patients admitted to the institute and diagnosed to have CSWS pattern on EEG was conducted. Spike and Wave Frequency/100 s(SWF) was calculated from sleep-EEG records. Language development and seizure outcomes were assessed at baseline and 1 year.

RESULTS

Fifty-two children were included (idiopathic CSWS, N = 19; symptomatic CSWS N = 33).The 2 groups differed in terms of younger age at seizure onset in symptomatic CSWS (p = 0.006), early age at language regression (p = 0.046), history of neonatal seizures (p = 0.038) and slowing of background activity on EEG (p = 0.024). Language regression was noted in 63.5 % of the cohort. Twenty-five (48%) patients received steroids with improvement in seizures (p < 0.001). Twenty-one (40.3 %) received steroids and intravenous immunoglobulin (IVIG) with improvement in seizure score (p = 0.002) at 1 year. Both immune-modulation arms irrespective of etiological subgroups had comparable proportions of children with expressive and receptive language gains. On 1 year follow-up, seizure remission was noted in 13(25 %) patients, with improved seizure score in 32/39 (61.5 %) patients and language improvement in 32 children (60.8 %). Patients with normal background on baseline EEG, generalised spikes, absent frontal-negative spikes and SWF < 170 were found to have improved language estimates on follow-up.

CONCLUSIONS

Despite clinical and therapeutic outcome differences between idiopathic and symptomatic CSWS, immune-modulation appears effective irrespective of aetiology. Analysis of EEG variables enables prediction of language outcomes at 1 year follow-up.

A study on spike focus dependence of high-frequency activity in idiopathic focal epilepsy in childhood

Objective

Spike foci in benign epilepsy with centrotemporal spikes (BECTS) are related to seizure semiologies, but this relationship is inconspicuous in Panayiotopoulos syndrome (PS). We analyzed spike‐associated high‐frequency activity (HFA) and its relationship to spike foci in the electroencephalograms (EEGs) of patients with BECTS and PS in order to elucidate the pathophysiology of these epileptic syndromes.

Methods

In 35 patients with BECTS and 29 with PS, focal spikes in scalp sleep EEGs were first classified by clustering according to their characteristics, including shape and distribution. For each patient, three or fewer spike clusters were investigated by time‐frequency spectral analysis and single‐dipole analysis using a realistic three‐dimensional head model to explore the relationships between the presence or absence of spike‐associated HFA and the distribution of estimated spike sources.

Results

A total of 159 spike clusters were analyzed (96 in BECTS and 63 in PS). HFA was detected in 73 spike clusters (76.0%) in BECTS and 37 (58.7%) in PS, with a significant difference in the proportion of spike clusters with HFA (p = 0.024 by Fisher's exact test). In BECTS, spikes had relatively uniform distributions, but the proportion of spikes with associated HFA was significantly higher in the spike group with dipoles in the perirolandic areas (42 of 49) than in that with dipoles outside of the perirolandic areas (23 of 36; p = 0.037). In PS, The proportion of spikes with associated HFA was significantly higher in the spike group with dipoles in the occipital lobes (20 of 26) than in that with dipoles outside of the occipital lobes (13 of 33; p = 0.020).

Significance

The proportion of spike‐associated HFA was higher in BECTS than in PS. Particular pathophysiological meaning was indicated in spikes with dipoles in the perirolandic areas in BECTS and in spikes with dipoles in the occipital lobes in PS owing to the high proportions of spike‐associated HFA in these areas.

Benign focal epilepsies of childhood

Until relatively recently, genetic influences in partial seizures were thought to be of minimal importance. However, with further identification of childhood benign partial seizures it is becoming clear that inheritance plays a major role in the pathogenesis of these seizures. Diagnostic criteria proposed for benign partial seizures include absence of neurologic or intellectual deficits, family history of epilepsy, onset of seizures after age 2 years, stereotyped brief seizures, frequent nocturnal occurrence, spontaneous remission in adolescence, and electroencephalograms (EEGs) demonstrating spikes with a distinctive morphology and localization superimposed on normal background activity. The two most commonly described benign partial epilepsies of childhood are benign Rolandic epilepsy (BRE) and benign occipital epilepsy (BOE). Both disorders begin in childhood, are associated with characteristic EEG patterns, have seizures that are easily controlled with medication, often are familial, and have an excellent prognosis. The other benign partial seizure disorders in children that have been described are not as well studied as BOE and BRE, and the role of inheritance pattern, if any, is less clear.

Characteristics of the synchronous occipital and frontopolar spike phenomenon in Panayiotopoulos syndrome

PURPOSE

The synchronous appearance of an occipital and frontopolar spike (the Fp-O spike) is characteristic of Panayiotopoulos syndrome (PS). This phenomenon is also seen in various other types of epilepsy, particularly those that occur in childhood. Using dipole analysis and sequential mapping, we investigated the characteristics of the Fp-O spike observed in seven patients with PS and six patients with symptomatic localization-related epilepsy in childhood (SLE).

METHODS

We analyzed both one averaged spike and 20 manually selected successive individual Fp-O spikes for each patient through sequential topographical mapping with steps of 10 ms from 40 ms before to 40 ms after the negative maximum peak of each spike. For dipole analysis, a period of 40 ms before the maximum negative peak of the averaged spike in each patient was examined using equivalent current dipole localization software.

RESULTS

Sequential mapping revealed that occipital negative peaks preceded frontal negative peaks in all of the PS patients, as well as in two of the six SLE patients. The four remaining SLE patients did not exhibit preceding occipital peaks. In all of the patients with PS, representative dipole locations were in the posterior area, whereas in SLE patients they were scattered over more anterior areas. The estimated sources of the Fp-O and O spikes appeared to have the same position and orientation in the two PS patients.

CONCLUSION

We conclude that Fp-O spikes in PS occur as the result of a rapid spread of epileptic activity from the posterior areas to the anterior areas of the brain. Fp-O spikes in PS patients show a uniform topographical pattern and dipole location, whereas those in other patients show more heterogeneity in these features. These findings support the homogeneity of PS and thus its designation as a syndrome.

EEG Dipole Characteristics in Panayiotopoulos Syndrome

PURPOSE

Panayiotopoulos syndrome (PS) is a type of benign childhood partial epilepsy that is frequently associated with abundant multifocal spikes other than main occipital spikes on the EEG. In this study, we investigated the characteristic features of dipoles in PS.

METHODS

We performed dipole analysis of the interictal occipital spike discharges seen in 10 children with PS (group A) and in 10 children with other types of symptomatic localization-related epilepsy (group B). We analyzed the dipoles of the averaged spike in each patient.

RESULTS

In group A, the averaged occipital spikes in each patient showed dense dipole locations in the mesial occipital area; in group B, widely scattered dipole locations were observed. In Group A, the geometric centers of the dipoles at each time point (such as at the main negative peak and before or after the main peak) were estimated in the neighboring locations. In contrast, they tended to be scattered in group B.

CONCLUSIONS

Our study reveals that PS has high dipole stability, similar to that of rolandic epilepsy. From the electroencephalographic view, this seems to indicate a close link between these two syndromes.

Dipole analysis in panayiotopoulos syndrome

Panayiotopoulos syndrome (PS) is a type of benign childhood partial epilepsy, which has a good prognosis despite the fact that it is frequently associated with abundant multifocal spikes on the electroencephalography (EEG). We investigated whether stable dipoles, as seen in rolandic epilepsy, were also present in PS. We performed dipole analysis of the interictal spike discharges seen in the interictal EEGs of eight children with PS. We chose more than 10 spikes for each kind of spike, and investigated whether or not more than three of these spikes showed consistently stable dipole locations. (1) We observed 15 different kinds of spikes in various regions in the EEGs of the eight children. (2) Twelve of the 15 kinds of spikes had dipoles with a high goodness of fit. Furthermore, 14 of the 15 spikes had stable dipoles with similar locations for more than three individual spikes. (3) Fourteen of the 15 spikes, including frontal spikes, showed dense dipole locations in the mesial occipital area. Thirteen of these 14 spikes also showed other dipole locations in the rolandic area and/or the vertex (Cz). Our study revealed that the various types of spikes observed in PS have similar and stable dipole locations. The dipoles showing high stability, were located in the mesial occipital area, and were accompanied by dipoles located in the rolandic area. The stability and location of these dipoles indicate that there may be a pathogenetic link between PS and rolandic epilepsy.

A comparison between averaged spikes and individual visually-analyzed spikes in rolandic epileptiform discharges

PURPOSE:This study compared some morphological features of individual rolandic epileptiform discharges, used to obtain an averaged estimate, with those of the resulting estimate. METHOD: Twenty-four averaged discharges from EEGs of 24 children showing rolandic spikes were compared with 480 individual discharges used in the averaging. The analysis was based on the occurrence of tangential dipole and "double spike" patterns. RESULTS: In 15 averaged discharges the tangential dipole pattern was found. Individual spikes used in the averaging process displayed the same pattern in 35-100% of them; in the remaining 9 averaged discharges, up to 20% of the individual spikes showed the same pattern, although this was not found in the averaged waveforms. "Double spike" pattern was found in 11 of the averaged waveforms and was recognized in 50-100% of its individual discharges, whereas up to 45% of individual spikes showed this pattern without expression in the averaged waveform. CONCLUSION: When visually analyzing an EEG with rolandic spikes, caution should be exercised in characterizing these patterns, since a few discharges showing them may not be expressed in the averaged waveform and the clinical correlations proposed for these patterns may not apply.

Time-related configuration change in benign focal epileptiform discharges of childhood: from a dipole to a negative monopole in a patient with generalized epilepsy

The case of a 6-year-old child with generalized epilepsy and benign focal epileptiform discharges (BFEDs) of childhood is presented. During his first EEG, performed when he was 6 years old, the patient had three staring episodes accompanied by bursts of 3-Hz spike-and-wave complexes. Interictally, frequent BFEDs were seen, configured as dipoles with a right temporal negativity and a right frontal positivity. The patient was administered ethosuximide and the staring spells disappeared. On follow-up EEG performed 2 years later, no generalized discharges were seen. However, the EEG again showed frequent spikes with a characteristic morphology of BFEDs. This time they were not configured as dipoles, but as monopoles with a maximum negativity over the right frontal region. The change in the generator's orientation over time (from a horizontal to a vertical dipole) is discussed, as well as the prognostic implications of the morphology and configuration of focal spikes. In addition, the authors review the coexistence of BFEDs and 3-Hz spike-and-wave complexes in their patient database.

Magnetoencephalographic study of giant somatosensory evoked responses in patients with rolandic epilepsy

We report five patients with rolandic epilepsy associated with giant somatosensory responses to median nerve stimulation, in whom we analyzed the pathophysiologic relationship between rolandic discharges and the somatosensory responses using magnetoencephalography. Four of the five patients showed giant P30m, the current source of which was localized in the primary somatosensory cortex, while the first cortical response, N20m, was not enhanced, except in one patient. The current source of the giant middle-latency component, N70m, was localized posterior to that of N20m, possibly in the posterior parietal cortex, in all patients. The initial positive peak and large negative peak of rolandic discharges were identical to P30m and N70m with respect to the current source localization, wave form, topographic pattern, and time relationship in the electroencephalogram and magnetoencephalogram, and somatosensory evoked magnetic field and somatosensory evoked potential records, respectively. In addition, the secondary sensory cortex was considered to be the generator of the middle-latency component in one patient. In one patient, the current intensity of the N70m was normalized along with clinical improvement and the disappearance of rolandic discharges, whereas those of other somatosensory evoked magnetic field components remained unchanged. Our data suggest that the rolandic discharge generator mechanism in these patients could be closely related to the developmental alteration of excitability in the primary somatosensory cortex, posterior parietal cortex, and secondary somatosensory cortex, which decreased with age, and it could share a common neuronal pathway, at least in part, with the giant P30m-N70m (N90m) in the somatosensory evoked magnetic field through the sequential and parallel processing of somatosensory information.

Dipole analysis of epileptic source generator with manual zero potential shifting method

The dipole tracing method is a technique whereby an electric source generator is estimated as an equivalent current dipole (ECD) based on potential distribution on the scalp. To estimate the electric source generator of low amplitude spikes, a manual zero potential shifting (MZPS) method was introduced in which a zero potential is set manually in dipole analysis. The subjects were three patients with localization-related epilepsy with temporal spikes. When low-amplitude spikes (< 50 microV) were analyzed by the conventional mean zero potential method, the dipolarity, an indicator of ECD reliability, had a low value and its locations were scattered. In contrast, when these low-amplitude spikes were analyzed by the MZPS method, ECD showed a high dipolarity value comparable to that obtained when high-amplitude spikes (> or = 50 microV) were analyzed by the mean zero potential method. Furthermore, the locations of the former ECD tended to converge and were almost identical to those of the latter ECD. These findings suggest the usefulness of the MZPS method in dipole analysis in terms of the dipolarity and ECD locations of low-amplitude spikes.

Clinical usefulness of the dipole tracing method for localizing interictal spikes in partial epilepsy

PURPOSE

To clarify the clinical usefulness of the dipole tracing method in evaluation of interictal EEG spikes in patients with partial epilepsy.

METHODS

Eight patients with partial epilepsy were studied. We compared the generator source of interictal spikes detected by the dipole tracing method with the results of magnetic resonance imaging (MRI), interictal/ictal measurement of cerebral blood flow (CBF) by single photon emission computed tomography (SPECT), interictal measurement of glucose metabolism by positron emission tomography (PET) and invasive electrocorticogram (ECoG).

RESULTS

In 5 patients with mesial temporal lobe epilepsy (TLE), including 3 patients who underwent standard temporal lobectomy, the dipole tracing method showed results consistent with those of other examinations and better correlation with ECoG than with other noninvasive examinations. In a patient with mesial TLE who had defects in the skull due to previous surgery, the dipoles were located more laterally than expected. In a patient with frontal lobe epilepsy (FLE) who was finally proved to have an epileptogenic area in the lateral frontal area, the spike dipoles were identified in the medial side of the frontal lobe.

CONCLUSIONS

The dipole tracing method used in the present study is useful for localizing epileptogenic areas in patients with mesial TLE. However, in patients with partial skull defects and in those with FLE, the reliability of this method is still in accuracy of the lobe level.

Initial estimation methods for dipole modeling in localization of epileptogenic focus

Although great sensitivities to initial estimates is an inherent feature of iterative dipole optimization algorithms, the study of better initial estimates has been neglected. For convergence to a correct solution, the initial estimates should be extremely close to the desired solution and be attributed to only a single dipole focus. To alleviate the interference of background and multiple foci, the singular value decomposition (SVD) technique is used initially to extract the dominant component of the EEG spike for dipole localization. By observing the three-dimensional topographic mapping, the initial estimates of the dipole parameter set can be computed from the intersection between the null potential plane and from the peak and valley potentials. This work also compares initial estimations of simulation data, including noisy data, noisy data with SVD process and noise-free data. Experimental results confirm that good initial estimates for the dipole parameters are necessary to ensure rapid convergence to the correct solution.

Topographic mapping and clinical analysis of benign childhood epilepsy with centrotemporal spikes

We studied the topographic mapping of the electroencephalography (EEG) of 47 children whose clinical history and course were compatible with typical benign childhood epilepsy with centrotemporal spikes (BCECT). Twenty-nine (62%) patients showed typical dipole fields, with a negative potential field in the centrotemporal region and a positive field in the frontal region. Eighteen children did not demonstrate the typical dipole field. Their non-dipole rolandic discharges were localized in small fields of centrotemporal region. The patients with dipole fields in BCECT had significantly less frequent seizures than patients without dipole fields. Twelve of the 47 patients with BCECT (26%) had more than one EEG focus. The clinical courses of patients with multiple foci were not worse than those of patients with a single focus. We conclude that EEG topographic mapping is helpful in identifying typical or atypical EEG topographic patterns in patients with clinically diagnosed BCECT. We also conclude that the presence of dipole field usually indicates a better clinical course of epilepsy and multiple foci do not mean a poor clinical course.

Transcranial magnetic stimulation in benign childhood epilepsy with centro-temporal spikes

Motor cortical excitability was studied using transcranial magnetic stimulation (TMS) in 10 age-matched controls, and 13 children with benign childhood epilepsy with centro-temporal spikes (BECT), with a mean age of 11.2 +/- 2.0 years (five untreated, and eight treated with sodium valproate (VPA) and well controlled). Motor evoked potentials (MEPs) elicited by TMS through a circular coil were recorded from the first dorsal interosseous muscle (FDI) while relaxed. There was no significant difference in latency or duration of MEPs, or central motor conduction time among controls, untreated and treated patients. The threshold intensity for TMS in the untreated patients (63.0 +/- 14.8%, mean +/- SD) was similar to that in controls (63.0 +/- 12.5%), while the threshold intensity in the treated patients (79.4 +/- 11.8%) was significantly higher than that in the other groups. A significant increase in threshold intensity (15 +/- 4.1%) was also observed in the untreated patients retested after starting VPA treatment. No adverse effects occurred during TMS in any subjects. Thus, motor cortical hyperexcitability in BECT was not recognized in the present TMS study, while VPA was confirmed to have an effect on the threshold intensity for TMS.

The functional organization of the interictal spike complex in benign rolandic epilepsy

PURPOSE

We studied the functional organization of the interictal epileptic spike complex in patients with benign rolandic epilepsy of childhood (BREC).

METHODS

We recorded interictal epileptiform spikes and somatosensory evoked potentials after median nerve stimulation, providing a biologic marker for the location of the central sulcus in 12 patients with BREC. We used multiple dipole modeling to assess the number, the three-dimensional intracerebral location, and the time activity of the underlying neuronal sources.

RESULTS

Although the interictal spike complex could be modeled by a single tangential dipolar source in seven patients (group 1), in the remaining five patients, two sources-a radial and a tangential dipole-were necessary adequately to explain the interictal spikes (group 2). The tangential source was located deeper than the radial source and was characterized by a frontal positivity and a centroparietal negativity with a phase reversal across the central sulcus, suggesting that the interictal spikes originated in the anterior wall of the central sulcus. The radial source showed a single electronegativity over the ipsilateral central region, which would be compatible with involvement of the top of either the pre- or postcentral gyrus. Both sources showed biphasic time patterns with an average latency difference of 30 ms.

CONCLUSIONS

Our results indicate that in some patients with typical BREC, the interictal epileptiform spike complex is generated by multiple, simultaneously active neuronal populations within the central region and that epileptiform activity is propagated between these two adjacent cortical areas.

Quantitative analysis of epileptic discharges

The methods for analysing the EEG epileptiform activity are discussed and compared. Particular emphasis is placed on studying interictal spike activity recorded from scalp. The results of these analyses should be interpreted in terms of underlying physiological events. An example is the hypothetical model of benign rolandic epilepsy of childhood.

Magnetoencephalographic analysis of rolandic discharges in benign childhood epilepsy

We report the detailed analysis of the generator and propagation of rolandic discharges in benign childhood epilepsy with centrotemporal spikes by means of 37-channel magnetoencephalography with neuromagnetic three-dimensional dipole localization. Equivalent current dipoles of prominent negative sharp waves of rolandic discharges appeared as tangential dipoles in the rolandic region, positive poles being situated anteriorly. These equivalent current dipoles showed a relatively limited localization and regular directions compared with other components. Equivalent current dipoles of preceding small positive waves, positive waves following negative sharp waves, and negative slow waves appeared in the vicinity of negative sharp waves. Equivalent current dipoles of rolandic discharges were located around the generator of somatosensory evoked magnetic fields stimulated at the lower lip. These findings suggest that rolandic discharges are generated through basically a mechanism similar to that for the middle-latency components of somatosensory evoked responses.

Spike dipole analysis using SEP dipole as a marker

In dipole localization analysis many problems remain which affect the accuracy of localization. We performed dipole estimation of spikes and SEP components in identical patients. The subjects are 8 cases of benign childhood epilepsy with centrotemporal spikes (BCECS), and two cases of temporal lobe epilepsy (TLE). In 8 of 10 cases, we also investigated dipoles using a 3-layer model in addition to a single layer (homogenous) model.

RESULTS

1) In 8 cases of BCECS, the spike dipoles were concentrated at the central line near the SEP dipoles, at a slightly fronto-lateral-downward position to the latter. The spike dipoles seemed to be situated at the bottom of the sensory cortex. 2) In two cases of TLE, the spike dipoles were located at the same coronal plane with the SEP dipoles, and more deeply seated mesially. The spike dipoles seemed to be at the bottom of the mesial temporal area. 3) Using 3-layer models, both the spike dipoles and the SEP dipoles located more superficially, while conserving the positional relationship with each other.

CONCLUSION

It is possible to more accurately define spike dipoles by using the SEP dipole as a marker.

Clinical application of spike averaging to dipole tracing method

As part of our studies on localization of epileptic foci, dipole analysis using averaged spikes were compared with that using individual spikes for 25 patients with localization related epilepsy. Our results are as follows. 1) In the group which showed stable dipoles from individual spikes, dipole localization from averaged and individual spikes were similar, although the former showed a higher dipolarity and more stable location, for the entire spike discharge including the peak, trough and wave. The high dipolarity was due to improved signal to noise ratio obtained from averaging. 2) The cases with centrotemporal spike focus including benign childhood epilepsy with centrotemporal spikes showed more reliable dipoles. In the cases with frontal lobe epilepsy, reliable dipoles were rarely obtained even with averaged spikes. Each method provided independent information, so they are of complementary value.