Focal Spikes Research Articles

Convulsions in tuberculous meningitis.

One-hundred-and-thirty-six children below 12 years of age hospitalized with a diagnosis of tuberculous meningitis (TBM) have been investigated to identify the underlying cause of convulsions. One-hundred-and-one children (74 per cent) presented with seizures before and/or during hospitalization. Generalized tonic and clonic seizures (GTCS) were the commonest (58 per cent) type of seizures followed by focal seizures (FS) (38 per cent) and tonic spasms (TS) (4 per cent). EEG changes were more frequently observed in cases with FS and in those children with GTCS who presented after first week of hospitalization. EEG findings included generalized dysrythmia with paroxysmal slow activity (38 per cent), interhemispheric asymmetry (23 per cent), multiple spike and wave pattern (10 per cent), and focal spike and wave pattern (15 per cent). CT scan findings were more common in those children with GTCS and TS who presented with recurrent seizures and/or seizures manifesting after first week of hospitalization. FS presenting at any stage of the disease were associated with CT scan abnormalities. Abnormalities detected in CT scan of brain included meningeal enhancement (55 per cent), hydrocephalus (32 per cent), tuberculomas (27 per cent), and cerebral infarctions (13 per cent). Clinical presentation and investigations indicate that the probable cause of convulsions could be attributed to cerebral edema (57 per cent), syndrome of inappropriate secretion of antidiuretic hormone (35 per cent), hydrocephalus (32 per cent), tuberculoma (27 per cent), abnormal electric focus (25 per cent), and cerebral infarction (13 per cent).

The estimation of the electrical sources of the focal spike and slow wave complex using the SSB dipole tracing method

The estimation of the electrical sources of the focal spike and slow wave complex using the SSB dipole tracing method

Long-term prognosis of Lennox-Gastaut syndrome.

We investigated the long-term prognosis of Lennox-Gastaut syndrome (LGS) in 72 patients followed up for > 10 years. Long-term seizure and intellectual outcomes were poor, as previously reported. The diagnosis of LGS was first made in the age range from 2 to 15 years with peak occurrence at 5 years. Progressive IQ score deterioration with age was apparent. At the last examination, 33% of patients with cryptogenic and 55% with symptomatic LGS had lost the characteristics of LGS, and their seizure disorders were classifiable as symptomatic generalized epilepsies, severe epilepsy with multiple independent spike foci, or localization-related epilepsies. Disabling drop attacks appeared in 46% of patients and tended to occur at older than 10 years. Gait deterioration was recognized in 12 patients and seemed to be due largely to progression of the epileptic encephalopathy. The gait disturbances, as well as increased frequency of violent drop attacks, were disabling in daily life and resulted in some patients being wheelchair bound.

Surface mapping of spike potential fields: experienced EEGers vs. computerized analysis

An EEG epileptiform spike focus recorded with scalp electrodes is clinically localized by visual estimation of the point of maximal voltage and the distribution of its surrounding voltages. We compared such estimated voltage maps, drawn by experienced electroencephalographers (EEGers), with a computerized spline interpolation technique employed in the commercially available software package FOCUS. Twenty-two spikes were recorded from 15 patients during long-term continuous EEG monitoring. Maps of voltage distribution from the 28 electrodes surrounding the points of maximum change in slope (the spike maximum) were constructed by the EEGer. The same points of maximum spike and voltage distributions at the 29 electrodes were mapped by computerized spline interpolation and a comparison between the two methods was made. The findings indicate that the computerized spline mapping techniques employed in FOCUS construct voltage maps with similar maxima and distributions as the maps created by experienced EEGers. The dynamics of spike activity, including correlations, are better visualized using the computerized technique than by manual interpretation alone. Its use as a technique for spike localization is accurate and adds information of potential clinical value.

Avoiding the pitfalls of EEG interpretation in childhood epilepsy.

The accurate interpretation of the electroencephalogram (EEG) of infants and children being evaluated for suspected epilepsy is based on the appreciation of normal and expected age-dependent characteristics, an awareness of the significance of both epileptiform and non-epileptiform activity, and the correlation of epileptiform abnormalities with clinical findings. Avoiding the pitfalls of pediatric EEG interpretation include the recognition of such normal EEG features in wakefulness as posterior slow waves of youth, mu rhythm, and lambda waves. In addition, the understanding of age-dependent characteristics of EEG state-changes is essential, such as: monorhythmic and paroxysmal hypnagogic hypersynchrony, special features of vertex transients and sleep spindles, positive occipital sharp transients, initial arousal responses and post-arousal hypersynchrony. The EEG response to activation procedures such as hyperventilation and photic stimulation may also be a source of confusion. Patterns of uncertain diagnostic significance also may be present in children, including 14- and 6-Hz bursts and rhythmic temporal theta bursts of drowsiness (the so-called psychomotor variant). Some nonepileptiform EEG abnormalities may also be misinterpreted as epileptiform. The determination of the clinical significance of spike foci and generalized abortive spike-and-wave may pose more of a problem as a potential pitfall than the identification by visual analysis of these interictal discharges. Another problem posed to the electroencephalographer is the determination of the EEG response to antiepileptic drug therapy including effect on spike foci, generalized spike-and-wave and electrical seizure activity, and effect on background activity. The recognition of the differences between the EEG of children and adults will provide the basis for more accurate interpretation and assist the electroencephalographer in avoiding the identification of normal, age-dependent features as epileptiform.

Source propagation of interictal spikes in temporal lobe epilepsy. Correlations between spike dipole modelling and [18F]fluorodeoxyglucose PET data.

Source localization methods were applied to interictal spikes from scalp EEGs and correlated with metabolic (PET scan) data in eight patients suffering from drug-resistant temporal lobe epilepsy (TLE). Dipolar sources, [18F]fluorodeoxyglucose (18FDG)-PET data and anatomical images (MRI) were projected into the same three-dimensional coordinates system. Averaged spikes were adequately modelled by two or three dipolar sources with different onset time of activation but overlapping activity (mean residual variance 3.4 +/- 2.1%). Although, in all patients, spike modelling demonstrated dipolar sources in both mesial and lateral temporal cortex, dipole propagation was consistent with the early involvement of only one of these two areas (mesio-temporal, five patients; lateral and polar neocortex, three patients). Six patients showed a unilateral interictal decrease in glucose uptake, as measured with 18FDG-PET, in the temporal lobe ipsilateral to the EEG spike focus. Temporal hypometabolism was bilateral in one patient and absent in the remaining case. When projected onto PET-scan slices, the dipolar sources of these patients were always included within the hypometabolic area. However, within the hypometabolic zone, the decrease in glucose uptake was not found to be more pronounced in regions containing dipoles. Therefore the spatio-temporal spread of neuronal hyperactivity underlying interictal spiking suggests the presence of preferential epileptogenic networks inside the hypometabolic temporal lobe. Fusion of bioelectric, metabolic and anatomical data proves to be a convenient way of summarizing multimodal information from non-invasive investigations in TLE patients entering an epilepsy surgery programme, and suggests that both interictal spike dipole modelling and 18FDG-PET data might be useful, as a complement to ictal electro-clinical data, in the presurgical evaluation of such patients.

Complexity of Focal Spikes Suggests Relative Epileptogenicity

The EEGs of 39 children with focal or multifocal spikes were subjected to singular value decomposition (SVD) as provided by a commercial software program. We noted that in children with spikes but no clinical seizures the variance accounted for by the first component averaged 91.9%, whereas in children with seizures it was 68.0% (p < .001). The first component accounted for 85.4% in children with single spike foci, for 71.5% in those with multifocal spikes, and for 61.4% (p < 0.002) in those with both focal spikes and generalized spike-wave complexes. Spikes in the frontal and frontopolar areas were the most complex, suggesting that at least in children they tend to be the partial expression of a generalized seizure tendency rather than a result of strictly local pathology.

Estimation of electrical sources of focal spike and slow wave complex by means of the 3-shell model dipole tracing (scalp-skull-brain model dipole tracing, SSB-DT)

Estimation of electrical sources of focal spike and slow wave complex by means of the 3-shell model dipole tracing (scalp-skull-brain model dipole tracing, SSB-DT)

PS-28-5 Dipole source estimation of focal epileptic spikes: correlation with stereo-electroencephalographic findings

PS-28-5 Dipole source estimation of focal epileptic spikes: correlation with stereo-electroencephalographic findings

A comparative study between dipole localizaation methods (DLM) and stereo-EEG (SEEG) applied to the analysis of focal epileptic spikes

A comparative study between dipole localizaation methods (DLM) and stereo-EEG (SEEG) applied to the analysis of focal epileptic spikes

Benign epilepsy of children with complex partial seizures following febrile convulsions

Among the partial epilepsies with complex partial seizures (CPS) following febrile convulsions (FC), there is an idiopathic epilepsy with extremely benign outcome, characterized by: 1) no past history suggesting brain insult, no underlying brain lesions, no neurological abnormalities, no mental retardation; 2) a high incidence of a positive family history of FC or benign epilepsy; 3) no past history of prolonged febrile convulsions; 4) EEG spike foci other than anterior temporal ones; 5) CPS easily controlled with full recovery.

Clinical and EEG features of partial epilepsy with secondary bilateral synchrony

We report clinical, EEG, and prognostic features of partial epilepsy (PE) with secondary bilateral synchrony (SBS) and their differences with respect to patients without this particular EEG pattern. The study group comprised 176 patients with symptomatic or cryptogenic PE. We evaluated age, sex. familiarity, etiology, age at epilepsy onset, seizure semeiology and frequency, radiologic data, mental status, and response to therapy. Forty-one of 176 patients exhibited focal spikes on EEG leading directly to SBS. Among all the variables analyzed, the following were significantly linked to SBS: young age at first observation, drug resistance, epileptic drop attacks, changes in seizure semeiology during epilepsy evolution, mental deterioration, progressive slowing of EEG background activity, and the presence of diffuse polyspike bursts during sleep. No other variables differed between partial epilepsy with or without SBS ( p > 0.05). Our data suggest that SBS may be considered an index of a severe outcome of PE and an EEG expression of a progressive epileptic involvement of the brain.

Epilepsy in children with Meningomyelocele

The medical records of 89 children followed at a multidisciplinary Meningomyelocele Clinic at the Children's Clinics for Rehabilitative Services were reviewed. Almost all children in southern Arizona with meningomyelocele are followed at this clinic. Eight children (foreign nationals) were excluded because they were not eligible for neurosurgery/neurology services at the clinic. The remaining 81 children have been followed at the clinic from 0.25 to 21 years. Seventeen children (21%; age: 1.3–17 years, mean: 9.1 ± 4.4 years; follow-up: 1.3–16 years) manifested seizures at some time during their course. All children with seizures had shunted hydrocephalus. Neonatal seizures occurred in 2 children currently not receiving medication. An additional 3 children had an acute symptomatic seizure associated with an intraventricular hemorrhage during ventriculoperitoneal shunt revision, 2 of whom later developed epilepsy. Fourteen children (17.3%) had epilepsy; 12 were taking antiepileptic drugs. Seizures were controlled on medication in 5 children. EEG abnormalities were present in 12 children (focal slowing 4, focal spikes 8, diffuse slowing 3, generalized or bilaterally synchronous spike-wave 4). Most of these children ( 12 14 ) had evidence of additional central nervous system (CNS) pathology (i.e., areas of encephalomalacia or past stroke 7, cerebral malformations 2, CNS calcifications 1, and frequent apneic spells/cardiac arrest 2). We conclude that epilepsy occurs in approximately 17% of children with meningomyelocele, and most have other CNS pathology to account for their seizures.

Temporal intermittent rhythmic delta activity in electroencephalograms.

Temporal intermittent rhythmic delta activity (TIRDA) has been reported to be highly specific for diagnosing complex partial epilepsy. Of 12,198 electroencephalographic (EEG) recordings performed at the Mayo Clinic between May 1, 1990 and May 1, 1991, 33 records from 27 patients (18 women and nine men; mean age, 41.5 years; range, 13-82 years) showed TIRDA. Clinical seizures were diagnosed in all patients, and complex partial epilepsy was well documented in 23. In a control group of 100 patients without TIRDA and matched for age and sex, generalized seizures were diagnosed in 25 and partial seizures in 15. Differences between TIRDA and control groups were highly statistically significant. Focal temporal sharp waves or spikes occurred in 23 patients with EEG recordings that contained TIRDA; three of these patients also exhibited generalized atypical spike-and-wave discharges. Four patients had TIRDA but no other epileptiform activity, although earlier EEGs of three of these patients contained spikes or sharp waves. These findings confirm earlier work, and we conclude that TIRDA represents an important epileptogenic abnormality.

Using the electric dipole model for localizing the EEG Spike Foci

Abstract A scheme, based on the four‐layer inhomogeneous spherical model of the head with an electric dipole in it, is proposed for localizing the epileptic focus. From the result of stability test, we find that the gradient project method used for computing an inverse solution of the model has a fast convergence speed. The convergence has very good stability which is not affected by different initial values. Spikes for three patients with different disorders are used for localizing the epileptic discharge sources. For the two patients with lateralized spikes, results from the dipole locations are very similar to the inspections by clinical physicians. However, for the other one with generalized spikes, we fail to localize the discharge source with acceptable accuracy. Thus, we conclude that the electric dipole model with the lateralized spikes is valuable in localizing epileptic discharge sources.

Tetanus toxin-induced seizures in infant rats and their effects on hippocampal excitability in adulthood

A new experimental model of developmental epilepsy is reported. Behavioral and EEG features of seizures produced by unilateral intrahippocampal injection of tetanus toxin in postnatal day 9–11 rats, are described. Within 24–72 h of tetanus toxin injection, rat pups developed frequent and often prolonged seizures which included combinations of repetitive wet dog shakes, and wild running-jumping seizures. Intrahippocampal and cortical surface EEG recordings showed that coincident with these behaviors, electrographic seizures occurred not only in the injected hippocampus, but also in the contralateral hippocampus and bilaterally in the neocortex. Analysis of the interictal EEG revealed multiple independent spike foci. One week following tetanus toxin injection, the number of seizures markedly decreased; however, interictal spiking persisted. After injection rats were allowed to mature some were observed to have unprovoked behavioral seizures and/or epileptiform EEG activity. Mature animals were also studied using in vitro slice techniques. Recordings from hippocampal slices demonstrated spontaneous epileptiform burst discharges in the majority of rats which had tetanus toxin induced seizures as infants. These events occurred in area CA3 and consisted of interictal spikes and intracellularly recorded paroxysmal depolarization shifts (PDSs). On rarer occasions, electrographic seizures were recorded. The use of the tetanus toxin model in developing rats may facilitate a better understanding of the unique features of epileptogenesis in the developing brain and the consequences early-life seizures have on brain maturation and the genesis of epileptic conditions in later life.

The Relation of Spike Foci and of Clinical Seizure Characteristics to Different Patterns of Mesial Temporal Atrophy

We reviewed clinical data and scalp electroencephalograms in 61 consecutive patients with temporal lobe epilepsy and mesial temporal atrophy assessed with volumetric magnetic resonance imaging: 39 patients had unilateral and 22 patients had bilateral atrophy. We attempted to determine whether any aspects of seizure symptoms and any electrographic features could be correlated to degree and anatomic pattern of mesial temporal atrophy. Spikes were always confined to temporal regions and were frequently bilateral without a statistically significant difference between patients with unilateral atrophy (33%) and those with bilateral atrophy (50%). Twenty-five of 40 foci associated with amygdala atrophy had maximum field over the anterior temporal regions. In contrast, 19 of 19 foci with isolated hippocampal formation atrophy were never maximum anteriorly. Secondarily generalized seizures and temporal lobe syncopes were correlated with anatomically extensive, particularly amygdala, atrophy. Prolonged postictal confusion was always associated with bitemporal abnormalities in the form of atrophy or spiking. These results explain some of the variability in the clinical and electrographic manifestations of temporal epilepsy and outline the specific role of amygdala involvement in addition to the commonly reported hippocampal atrophy.

Spontaneous potentiation of focal potentials of the CA1 field in long-surviving hippocampal slices of the rat in the absence of electrical stimulation.

The changes in the efficiency of the synaptic transmission in the Schaffer collaterals-field CA1 neurons pathways following prolonged deprivation of afferentation, the cessation (up to four hours) of stimulation of the tested input with brief series of tests every hour (the control afferent inputs, were stimulated throughout the entire experiment at a frequency of 0.05/sec), were investigated in surviving slices of the hippocampus of rats. The evoked focal potentials, population spikes (PS) and population excitatory postsynaptic potentials (pEPSP) were recorded. The prolonged cessation of stimulation led to a significant (p < 0.001) increase in the amplitude of the PS (up to 208% in relation to the baseline level). This phenomenon of potentiation was specific in relation to input and exhibited the properties of "E-S potentiation". A hypothesis is advanced regarding the association of mechanisms responsible for the development of "deprivational" potentiation and of the late phase of long-term posttetanic potentiation.

Multifocal Independent Spike Syndrome: Relationship to Hypsarrhythmia and the Slow Spike-Wave (Lennox-Gastaut) Syndrome

During a 3 year period EEGs were performed in 64 children with multifocal independent spikes (MIS), 17 with slow spike-wave complexes (SSWC), 22 with MIS and SSWC and 15 with hypsarrhythmia. Only EEG records containing adequate wakefulness and sleep were analyzed in 40 children with two or more serial EEGs at least 5 months apart. Transitions from one pattern to another occurred in 25/40 patients, consistent in all cases with the following sequence: Hypsarrythmia-->MIS-->MIS and generalized discharges-->SSWC. Patients with and without transitions did not differ in their age at presentation or duration of follow-up. Eleven of 12 patients whose initial EEG showed hypsarrhythmia or multifocal independent spikes underwent transitions, compared to 0/8 patients with SSWC (p < 0.001), indicating that SSWC is a stable pattern in children. Over a 6 month period, we also prospectively analyzed EEGs of 20 patients with multifocal spikes, hypsarrhythmia, and slow spike-wave complexes. Sleep activated additional spike foci, increased the frequency of generalized spike discharges and produced synchronization of bitemporal and bifrontal spike-wave discharges at 1.5-2.5 Hz the same as SSWC.

Epileptic EEG Discharges During Burst Suppression*

Barbiturate anaesthesia is used in the treatment of status epilepticus and severe epilepsy of children. EEG is then used as a measure of the depth of anaesthesia, burst suppression being an easily identified EEG pattern. In this case report we describe epileptiform discharges during EEG suppression in two children undergoing barbiturate anaesthesia for treatment of intractable seizures. One of them had focal, rhythmic discharges of negative spikes on the positive suppression level. Bursts were readily produced by visual stimuli with flashes of red light but this did not increase the frequency of focal spike discharges after bursts. The other patient had generalised, high amplitude spike-wave complexes, which were easy to distinguish from the bursts. We emphasise that it is important to make a distinction between electrocerebral silence, or isoelectric EEG as it was previously called, from EEG suppression. It is also important to distinguish epileptiform discharges from bursts, if the intention is to keep the anaesthesia at EEG burst suppression level.