Anders Hedström

Intractable Epilepsy in a Population-Based Series of Mentally Retarded Children

Summary: Purpose: The characteristics of intractable epilepsy were analyzed in a population‐based study of active epilepsy in mentally retarded children aged 6–13 years.

Epidemiology of absence epilepsy: EEG findings and their predictive value

This population-based study of absence epilepsy comprised 97 children, ranging in age from newborns to 15 years. All had regular bilaterally synchronous and symmetric 2-4 Hz spike-and-slow wave discharges and absences with or without generalized tonic-clonic seizures (GTCS). Patients without GTCS tended to have long episodes of 2-4 Hz spike-and-slow wave discharges (greater than or equal to 10 sec), and simultaneous clinical correlates more frequently than those with GTCS. Posterior delta rhythm was found only in patients without GTCS. Focal abnormalities, albeit transient, were more frequent among patients with GTCS. The initial electroencephalogram was of some early predictive value in patients with only absences at the time of the initial registration. Brief episodes of 2-4 Hz spike-and-slow wave (less than 10 sec) without clinical correlates were associated with a slightly increased risk of future GTCS.

The effects of epilepsy surgery on the sensorimotor function of children.

The motor and sensory functions of 50 children were investigated before and six months after epilepsy surgery; 34 infants were assessed 24 months after surgery. Postoperatively, 20 children were seizure‐free and 22 had a significant reduction of seizures. Epilepsy surgery was found to be an effective mode of treatment for intractable seizures in childhood, even in multiply handicapped individuals. Motor and sensory functions did not deteriorate after surgery; in fact, significant improvements were found in more than half of the children, including those with multiple handicaps. Improvements were most obvious in the seizure‐free group, but were also noted in those with reduced seizure frequency. The younger children benefited more from surgery as regards sensorimotor function than did older children and adolescents.

Particle Swarm Optimization Applied to EEG Source Localization of Somatosensory Evoked Potentials

One of the most important steps in presurgical diagnosis of medically intractable epilepsy is to find the precise location of the epileptogenic foci. Electroencephalography (EEG) is a noninvasive tool commonly used at epilepsy surgery centers for presurgical diagnosis. In this paper, a modified particle swarm optimization (MPSO) method is used to solve the EEG source localization problem. The method is applied to noninvasive EEG recording of somatosensory evoked potentials (SEPs) for a healthy subject. A 1 mm hexahedra finite element volume conductor model of the subjects head was generated using T1-weighted magnetic resonance imaging data. Special consideration was made to accurately model the skull and cerebrospinal fluid. An exhaustive search pattern and the MPSO method were then applied to the peak of the averaged SEP data and both identified the same region of the somatosensory cortex as the location of the SEP source. A clinical expert independently identified the expected source location, further corroborating the source analysis methods. The MPSO converged to the global minima with significantly lower computational complexity compared to the exhaustive search method that required almost 3700 times more evaluations.

Application of particle swarm optimization in epileptic spike EEG source localization

Surgical therapy has become an important therapeutic alternative for patients with medically intractable epilepsy. Correct and anatomically precise localization of an epileptic focus is essential to decide if resection of brain tissue is possible. The inverse problem in EEG-based source localization is to determine the location of the brain sources that are responsible for the measured potentials at the scalp electrodes. We propose a new global optimization method based on particle swarm optimization (PSO) to solve the epileptic spike EEG source localization inverse problem. In a forward problem a modified subtraction method is proposed to reduce the computational time. The good accuracy and fast convergence are demonstrated for 2D and 3D cases with realistic head models. The results from the new method are promising for use in the pre-surgical clinic in the future.

Non-invasive EEG source localization using particle swarm optimization: A clinical experiment

One of the most important steps of pre-surgical diagnosis in patients with medically intractable epilepsy is to find the precise location of the epileptogenic foci. An Electroencephalography (EEG) is a non-invasive standard tool used at epilepsy surgery center for pre-surgical diagnosis. In this paper a modified particle swarm optimization (MPSO) method is applied to a real EEG data, i.e., a somatosensory evoked potentials (SEPs) measured from a healthy subject, to solve the EEG source localization problem. A high resolution 1 mm hexahedra finite element volume conductor model of the subjects head was generated using T1-weighted magnetic resonance imaging data. An exhaustive search pattern and the MPSO method were then applied to the peak of the averaged SEPs data. The non-invasive EEG source analysis methods localized the somatosensory cortex area where our clinical expert expected the received SEPs. The proposed inverse problem solver found the global minima with acceptable accuracy and reasonable number of iterations.

Remote sessions and frequency analysis for improved insight into cerebral function during pediatric and neonatal intensive care

A project involving recording and analysing EEG together with cardiovascular signals and temperature has been initiated. The aim of this project is to establish difficulties and possibilities involved with implementing a system for remote sessions and analysing EEG in correlation with other physiological signals. One objective is to find indicators of cerebral function during postasphyxia neonatal intensive care and pediatric cardiopulmonary bypass surgery with hypothermia. Remote sessions for joint interpretation have been carried out between pediatricians and clinical neurophysiologists, and EEG has been analyzed using frequency analyzing tools. One result is the discovery of reversible spectral changes coinciding with blood pressure falls, which may indicate loss of autoregulation function. This finding is one outcome from initial use of a system, developed during the project to facilitate communication about, and analysis of the recorded signals. Thus, already from a limited number of remote sessions and the use of basic signal processing techniques, important results have been achieved and better insight has been gained of how cerebral function is affected by cardiopulmonary bypass surgery. In this paper, we present our experiences from introducing a system for remote consultations, and evaluate the use for such a system in the current applications.

Advances in neuro diagnostics based on microwave technology, transcranial magnetic stimulation and EEG source localization

Advances in neuro diagnostics based on microwave antenna system in terms of a helmet including a set of broad band patch antennas is presented. It is shown that classification algorithms can be used to detect internal bleeding in stroke patients. Transcranial magnetic stimulation has traditionally been used for brain mapping and treatment of depression. In this paper we discuss the use of the method for neuro diagnostics with the help of integrated image guidance. Surgical therapy has become an important therapeutic alternative for some patients with medically intractable epilepsy. Electroencephalography and the associated model based diagnostics as a non-invasive diagnostic tool is also discussed.

Successful epilepsy surgery in a patient with neurosarcoidosis.

This case concerns a patient with generalized neurosarcoidosis and pharmacoresistant focal epilepsy. Although immunosuppressive therapy resulted in remission of the neurosarcoidosis, seizures continued and were shown to originate from the right temporal lobe (TL). The patient underwent a right anterior temporal lobe resection (TLR) and obtained >90% reduction of seizure frequency.

Epilepsy surgery in children with accompanying impairments

The aim of this study was to assess seizure outcome 2 years after epilepsy surgery in a consecutive series of paediatric patients, with special focus on children with learning disabilities and other neuroimpairments in addition to the epilepsy. Outcome 2 years after surgery was assessed in 110 of 125 children operated upon for drug resistant epilepsy in Gothenburg 1987-2006. More than half of the children had learning disabilities, 43% motor impairments and 30% a neuropsychiatric diagnosis. Fifty-six per cent of those with an IQ < 70 became seizure-free or had a >75% reduction in seizure frequency, and two thirds if the operation was a resection. The corresponding figure in those with more than 100 seizures per month was 15 out of 31, and another seven had a 50-75% reduction in seizure frequency. The message is that learning disability, motor impairment and psychiatric morbidity should not be contraindications for paediatric epilepsy surgery. More than half of the children with learning disabilities had a worthwhile seizure outcome, with even better results after resective surgery. Children with drug resistant epilepsy and additional severe neurological impairments should have the benefit of referral to a tertiary centre for evaluation for epilepsy surgery.