Extreme somatosensory evoked potentials (ESEPs) elicited by tapping of hands or feet in children: a somatosensory cerebral evoked potentials study

Six children with tactile-evoked spikes in the EEG, also defined as extreme somatosensory evoked potentials (ESEPs), underwent an SEPs study in order to define the characteristics of such evoked potentials. Short-latency SEPs showed normal mean latency and amplitude values. Mid- or long-latency SEPs of abnormally high amplitude were recorded after stimulation of one or more extremities. Such extreme responses which showed the same reactivity proper to normal long-latency SEPs could be considered to correspond to the evoked spikes in the EEG.     

Combined EEG and MEG analysis of early somatosensory evoked activity in children and adolescents with focal epilepsies.

OBJECTIVE: The study aimed to evaluate differences between EEG and MEG analysis of early somatosensory evoked activity in patients with focal epilepsies in localizing eloquent areas of the somatosensory cortex. METHODS: Twenty-five patients (12 male, 13 female; age 4-25 years, mean 11.7 years) were included. Syndromes were classified as symptomatic in 17, idiopathic in 2 and cryptogenic in 6 cases. 10 patients presented with malformations of cortical development (MCD). 122 channel MEG and simultaneous 33-channel EEG were recorded during tactile stimulation of the thumb (sampling rate 769 Hz, band-pass 0.3-260 Hz). Forty-four hemispheres were analyzed. Hemispheres were classified as type I: normal (15), II: central structural lesion (16), III: no lesion, but central epileptic discharges (ED, 8), IV: lesion or ED outside the central region (5). Analysis of both sides including one normal and one type II or III hemisphere was possible in 15 patients. Recordings were repeated in 18 hemispheres overall. Averaged data segments were filtered (10-250 Hz) and analyzed off-line with BESA. Latencies and amplitudes of N20 and P30 were analyzed. A regional source was fitted for localizing S1 by MRI co-registration. Orientation of EEG N20 was calculated from a single dipole model. RESULTS: EEG and MEG lead to comparable good results in all normal hemispheres. Only EEG detected N20/P30 in 3 hemispheres of types II/III while MEG showed no signal. N20 dipoles had a more radial orientation in these cases. MEG added information in one hemisphere, when EEG source analysis of a clear N20 was not possible because of a low signal-to-noise ratio. Overall N20 dipoles had a more radial orientation in type II when compared to type I hemispheres (p=0.01). Further N20/P30 parameters (amplitudes, latencies, localization related to central sulcus) showed no significant differences between affected and normal hemispheres. Early somatosensory evoked activity was preserved within the visible lesion in 5 of the 10 patients with MCD. CONCLUSIONS: MEG should be combined with EEG when analyzing tactile evoked activities in hemispheres with a central structural lesion or ED focus. SIGNIFICANCE: At time, MEG analysis is frequently applied without simultaneous EEG. Our results clearly show that EEG may be superior under specific circumstances and combination is necessary when analyzing activity from anatomically altered cortex.     

Somatosensory evoked potential testing in infants and children.

Somatosensory evoked potentials (SSEPs) provide the means to assess noninvasively the peripheral and central nervous system in infants and young children. As experienced clinicians know, this is the very system most difficult to adequately evaluate in young children. Physical examination is difficult. SSEPs provide information about function of somatosensory systems not otherwise available. In addition to pathologic states, maturation and sleep produce changes in SSEPs that require careful analysis.     

Systematic approach to dipole localization of interictal EEG spikes in children with extratemporal lobe epilepsies.

OBJECTIVES: To assess the reliability of dipole localization based on residual variances (RV), using equivalent current dipole analysis of interictal EEG spikes in children with extratemporal lobe epilepsy. METHODS: Four pediatric patients with extratemporal lobe epilepsy were studied. Digital EEG was recorded from 19 scalp electrodes. Computer programs for spike detection and clustering analysis were used to select spikes. Dipoles were calculated 5 times for each spike using different initial guesses by the moving dipole model. Standard deviation (SD) of the dipole positions was calculated at each time point in the 5 trials. RESULTS: We analyzed the dipoles at 1097 time points from 4 patients. Among 106 time points with RV < 2%, the SD was < 1 mm in 78 (74%), while in those with SD > 1 mm the dipole positions varied between 2.8 and 52.6 mm. Of dipoles with RV < 1%, 26 of 27 (96%) had an SD < 1 mm; the one dipole with SD > 1 mm varied within 2.5 mm. The dipole localizations with RV < 2% corresponded to the epileptogenic zones identified on intracranial invasive video EEG and intraoperative ECoG. CONCLUSIONS: The systematic approach of equivalent current dipole analysis using spike detection, clustering analysis, and an RV < 2% as a standard is useful for identifying extratemporal epileptic regions.     

Somatosensory evoked spikes and epileptic seizures: a study of 385 cases.

We examined 385 children whose EEG showed high voltage potentials evoked by taps applied to one or both feet or hands (SES). The relationship between characteristics of SES and the occurrence of epileptic seizures and the characterization of epileptic syndromes were studied. Ninety-one children (23.6%) had epilepsy, 42 (10.9%) had only febrile convulsions and 252 children had other complaints. Epilepsy occurred in a higher proportion of cases when: SES by foot tapping were multiphasic, with high amplitude or SES were obtained by hand stimulation and there was spontaneous epileptiform activity in the EEG. The following epileptic syndromes were diagnosed: benign childhood epilepsy with centrotemporal spikes in 21 cases, benign epilepsy of childhood with occipital paroxysms in 2, benign psychomotor epilepsy in 1, "partial idiopathic others" in 43, generalized idiopathic in 8, symptomatic epilepsies in 13 and undetermined in 3 cases. In most cases SES were observed in children without evidence of cerebral organic lesion, suggesting the existence of an age-related, functional mechanism. Some characteristics of SES and the occurrence of spontaneous epileptiform activity showed a positive association with epileptic seizures. SES occurred in different types of partial and generalized epilepsies of childhood but in nearly 50% of the cases with epilepsy, there was a benign condition involving mainly the parietal lobe with versive, unilateral and sleep-generalized seizures.     

High-frequency oscillations in a spectrum of pediatric epilepsies characterized by sleep-activated spikes in scalp EEG

ObjectiveWe studied ripple-band (80–200 Hz) high-frequency oscillations in scalp electroencephalogram (EEG) in various pediatric epilepsies featuring sleep-activated spikes, such as epileptic encephalopathy with continuous spike-and-wave during sleep (CSWS) and investigated their characteristics.MethodsThe subjects were 94 children with epileptic disorders including idiopathic and non-idiopathic CSWS, benign epilepsy with centrotemporal spikes (BECTS), Panayiotopoulos syndrome, other types of focal epilepsies (oFE), and focal spikes without clinical seizures (Latent). We detected ripple oscillations using a semi-automatic detection tool based on localized power increase.ResultsIn the idiopathic CSWS Group, the median ratio of ripples per spike in the initial EEG was 5.73, which was significantly higher than those in the BECTS, Panayiotopoulos syndrome, oFE, and Latent Groups (0.39, 0.02, 0.35, 0, respectively, all with p < 0.01). Ripples were particularly frequent at younger ages.ConclusionsThis paper is the first to confirm a high ratio of ripples per spike in CSWS in the largest number of patients to date.SignificanceThe dense generation of ripples, which occurs through a combination of heavy loading of individual spikes with ripples and large numbers of spikes during sleep, characterizes CSWS and might be closely related to the pathophysiology of this epileptic encephalopathy.     

Somatosensory evoked potential measures of conduction in peripheral and central pathways in children with protein-calorie malnutrition

The effects of malnutrition on conduction in peripheral and central somatosensory pathways in humans, as measured by short-latency somatosensory evoked potentials (SEPs) have not been previously reported. A group of 28 children with kwashiorkor were compared to a control group of 35 children, aged 6-36 months. The malnourished group had longer reciprocal conduction velocities (ms/m) for pathways between the wrists and the brachial plexi (CL1 response) and between the brachial plexi and the upper cervical region (CL1-CVN). While an individual child with kwashiorkor had abnormal intracranial reciprocal conduction velocities (CVN-N1), the inter-group differences did not attain statistical significance, possibly due to inadequate indices of central pathway lengths. These findings expand the extent of conduction delays revealed by previous studies of peripheral nerve conduction velocities in PCM.     

Spontaneous EEG spikes in the normal hippocampus. III. Relations to evoked potentials

Spontaneous EEG spikes (SPKs) were recorded from the CA1 region of the dorsal hippocampus in normal rats during behavioral states not accompanied by rhythmical slow activity (RSA). SPKs were positive in stratum oriens, negative in stratum radiatum and accompanied by population bursts (PBs) in stratum pyramidale. In order to examine the origin of SPKs and PBs single pulse or brief high frequency electrical stimuli were applied to the Schaffer collateral/commissural pathway. Evoked potentials were recorded and compared with spontaneous SPKs and PBs. The results indicate the following: (1) the laminar amplitude profile of spontaneous SPKs was similar to that of population EPSPs evoked by stimulation of the Schaffer collateral/commissural pathway; (2) the population EPSP most similar to the spontaneous SPK was evoked by a brief (20-60 msec) train of high frequency (125-500 Hz) pulses; (3) the same pattern of stimulation was also found to be most efficient in evoking a series of multiple population spikes resembling a type of spontaneous PB (ripple). These observations suggest that SPKs and PBs in CA1 represent population EPSPs and multiple population spikes, respectively and that these CA1 events are triggered by brief, high frequency burst discharges of CA3 pyramidal cells via the Schaffer collateral and commissural pathway.     

Interhemispheric threshold differences in idiopathic generalized epilepsies with versive or circling seizures determined with focal magnetic transcranial stimulation

The interhemispheric difference of the motor-cortical threshold (IDMT) was studied with focal magnetic transcranial stimulation (TCS) in ten patients with idiopathic generalized epilepsy (IGE) who also displayed versive or circling seizures (IGEvc). The data were compared with those obtained from two control groups; 13 patients with IGE without asymmetrical motor seizures, and 25 normal volunteer subjects. The IDMT, referred to as the percentage of maximum stimulator output, was assessed by focal TCS applied to the hand areas. Seven patients with IGEvc and only one patient with IGE had an interhemispheric motor threshold beyond the normal range. The IDMT in IGEvc patients was significantly higher compared to that of IGE patients and normal individuals. An interhemispheric imbalance of cortical excitability may explain lateralized ictal motor manifestations in patients with IGEvc.     

High incidence of language disorder in children with focal epilepsies

To investigate the relationship between the presence of language disorder, type of epilepsy, and epileptic seizures in childhood, language levels, types of language impairment, and aetiologies were examined in 109 children, aged between 5 and 17 years, attending a national children's epilepsy assessment unit over a 4-year period. There were 70 males and 39 females. Median age was 11 years 4 months (range 5 to 18 years 9 months). In addition to neurological assessment, simultaneous video and EEG monitoring and prolonged ambulatory EEG, each child underwent a comprehensive series of multidisciplinary tests, including intelligence, language, and communication assessments. Classification of seizures and epilepsy syndromes was agreed in conference by a physician specializing in childhood epilepsies, a paediatric neurologist, and a neuropsychiatrist. Other test procedures were administered by a speech and language pathologist with assistance from a neuropsychologist when relevant. Level of language disability in these children was associated with a range of aetiological factors. Evidence was found of a significant number of associations between focal epilepsies, certain seizure types, and language disorder. Of the 46 (42.2%) children with language disorders in the research sample, 30 had localization-related epilepsies and a further three had epilepsies which were undetermined as to whether focal or generalized. Children with focal epilepsies were 30% more likely to have language disorder than other language disability subtypes. The research demonstrated a clear though often subtle association between focal (localization-related) epilepsy and language disorder, indicating an increased risk in this patient group. Children with simple or complex partial seizures were more likely to have language disorder than other language disability subtypes; they also tended to have the lowest number of seizure types per case. This is of importance to clinicians managing children with epilepsy and has implications for their educational and social welfare.     

EEG and evoked potentials in HIV-infected children.

Forty-seven HIV-seropositive children were investigated by EEG and evoked potentials (BAEP, SEP). Twenty-three children were symptomatic (P2), 8 seropositive without symptoms (P1), and 16 children were less than 15 months of age (P0). Some of them were investigated at different stages of HIV infection. During the neonatal period, 7 newborns of drug-addicted mothers had seizures and frequent spikes and sharp waves in their EEGs. Among (P2) children 6/23 showed background slowing and 1 had rhythmic theta activity (6 with and 1 without neurological symptoms). In BAEP, bilateral prolonged interpeak latencies (IPL) were found in 1 child with severe AIDS encephalopathy. Side differences greater than or equal to 0.4 ms in IPL were seen in 2 (P2), 1 without and 1 with neurological symptoms. A late onset was seen in 2 (P1) and 4 (P2) children. Median SEPs were normal in 24/26 patients; N20/N13 amplitude ratio was reduced in 2 (P1) patients. EEG and BAEP revealed nonspecific abnormal features in HIV encephalopathy. The the progression of the disease. However, also in the symptomatic group, normal results of EEG and BAEP dominated. SEP in the symptomatic group revealed only normal values. For monitoring the effectiveness of AZT treatment in HIV encephalopathy, EEG seems to be a relevant investigation; for evoked potentials more data and experience are needed.     

EEG and the variance of motor evoked potential amplitude.

The motor threshold is an important parameter in selecting the treatment intensity of patients undergoing transcranial magnetic stimulation. The large variance in magnitude of motor evoked responses has forced clinicians to perform many trials and average the results to find a repeatable value for motor threshold. Our objective is to investigate the source of the variance in amplitude. Four clinically healthy adult males participated in an EEG and EMG during transcranial magnetic stimulation of the left motor cortex, 100% motor threshold, 0.1 Hz. Per our hypothesis, a significant negative correlation of .22 was found between the amplitude of the motor evoked potential and the power in the high alpha frequency band during the pre-stimulus period (p < .001). In addition, a significant positive correlation of .17 was found between the motor evoked potential (MEP) amplitude and the gamma band (p < .001). The strongest correlation of .27 (p < .001) was found between the MEP amplitude and the ratio of the power in the low gamma to high alpha band. We conclude that the gamma to alpha power ratio may be a useful indicator of cortical excitability.     

Valproate reduces spontaneous generalized spikes and waves but not photoparoxysmal reactions in patients with idiopathic generalized epilepsies

Purpose: Patients with idiopathic generalized epilepsies (IGEs) often present with interictal spike‐wave discharges (SWDs) at rest (spontaneous SWDs), during hyperventilation, and in response to photic stimulation (photoparoxysmal response or PPR). Valproic acid (VPA) is a first‐line antiepileptic drug for therapy of patients with IGE. Herein we investigated the effect of VPA on all three types of SWDs in children and adolescents with IGE. Methods: Routine electroencephalography (EEG) during wakefulness, which was recorded before VPA monotherapy and up to four times during the first year of the VPA treatment, was analyzed retrospectively. For the analysis of the VPA effect on spontaneous SWDs and SWDs under hyperventilation, the number and duration of SWDs were counted. SWDs under intermittent photo stimulation (IPS) were classified according to the extent of propagation (grading). Response to VPA treatment (rest/hyperventilation) was defined as a disappearance of SWDs within the year after VPA introduction. Key Findings: Eighty‐four patients (37 male and 47 female, mean age 9.5 ± 4.1 years) exhibited spontaneous SWDs or SWDs under hyperventilation. From this sample, 34 patients exhibited the PPR (7 male and 27 female, mean age 10.1 ± 3.9 years). A significant reduction in the number and duration of spontaneous SWDs and SWDs under hyperventilation was observed in the first 6 weeks of treatment (p ≤ 0.001, corrected, 87.3% responders). This effect remained stable over the 1 year observation period. Concerning PPR, only 4 (12.9%) of 31 patients were classified as responders. The difference between groups of patients with spontaneous/induced SWDs and PPR according to the number of responders was significant (p < 0.001). Significance: This study provides evidence that the effect of VPA on SWDs differs dependent on the types of SWDs. In the majority of patients, spontaneous SWDs and SWDs induced by hyperventilation disappeared, whereas the PPR mostly remained under VPA treatment. These results point to different pathogenetic mechanisms underlying the spontaneous and the evoked generalized epileptic activity in the EEG.