C. Viteri

Independent component analysis as a tool to eliminate artifacts in EEG: A quantitative study

Summary Independent component analysis (ICA) is a novel technique that calculates independent components from mixed signals. A hypothetical clinical application is to remove artifacts in EEG. The goal of this study was to apply ICA to standard EEG recordings to eliminate well-known artifacts, thus quantifying its efficacy in an objective way. Eighty samples of recordings with spikes and evident artifacts of electrocardiogram (EKG), eye movements, 50-Hz interference, muscle, or electrode artifact were studied. ICA components were calculated using the Joint Approximate Diagonalization of Eigen-matrices (JADE) algorithm. The signal was reconstructed excluding those components related to the artifacts. A normalized correlation coefficient was used as a measure of the changes caused by the suppression of these components. ICA produced an evident clearing-up of signals in all the samples. The morphology and the topography of the spike were very similar before and after the removal of the artifacts. The correlation coefficient showed that the rest of the signal did not change significantly. Two examiners independently looked at the samples to identify the changes in the morphology and location of the discharge and the artifacts. In conclusion, ICA proved to be a useful tool to clean artifacts in short EEG samples, without having the disadvantages associated with the digital filters. The distortion of the interictal activity measured by correlation analysis was minimal.

Independent component analysis removing artifacts in ictal recordings

Summary:  Purpose: Independent component analysis (ICA) is a novel algorithm able to separate independent components from complex signals. Studies in interictal EEG demonstrate its usefulness to eliminate eye, muscle, 50‐Hz, electrocardiogram (ECG), and electrode artifacts. The goal of this study was to evaluate the usefulness of ICA in removing artifacts in ictal recordings with a known EEG onset.

Late-onset periodic asystolia during vagus nerve stimulation.

Cardiac changes may occasionally occur during vagus nerve stimulation (VNS) used in epileptic patients. As they can be potentially life‐threatening, it is important to detect them, and this is why an intraoperative test is performed during the implantation. Few cases of asystole during this test have been described. Only one patient with late‐onset bradyarrythmia caused by VNS has been reported. This patient had been implanted 2 years and 4 months before the episode. We present another case of late asystole in a patient whose VNS had been implanted 9 years before the arrhythmia onset. In our patient, each run of stimulation produced bradyarrhythmias and very often severe asystolia due to atrium‐ventricular block.

Progabide Treatment in Severe Epilepsy: A Double‐Blind Cross‐over Trial Versus Placebo

Summary: Twenty therapy‐resistant epileptic patients entered a double‐blind, randomized, two‐period, crossover trial comparing progabide (19.3–36 mg/kg/day) and placebo as add‐on drugs to standard therapy. Each period lasted 6 weeks with a gradual crossover during 4 days. Five patients were dropped because of reasons unrelated to treatment. Among the 15 patients who completed the study, seven had partial, six primary generalized, and two secondary generalized epilepsies. Preexisting antiepileptic drugs (AEDs) ranging from one to three per patient (mean 2.2 AEDs/patient) were maintained unchanged during the trial. Efficacy was assessed biweekly by means of total seizure counts, counts of each seizure type, and global clinical judgment. At the same time intervals, safety was assessed by means of reports of adverse events, clinical and neurological examination, laboratory tests, and measurement of plasma concentrations of progabide and associated AEDs. According to the clinical global judgment, eight patients were considered improved during progabide treatment. Seizures were reduced in 14 of 15 patients during the progabide as compared with the placebo period. During the progabide period, the reduction of the total seizure count was 45 and 58% in two patients and 88–97% in six patients. A significant reduction of the total seizure number was observed in the progabide period as compared with the placebo period, both in the whole patient group (p <0.01) and in the two subgroups of patients with generalized (p <0.01) and partial (p <0.05) epilepsies. Absences, major generalized, and partial seizures (including partial seizures with secondary generalization) were significantly reduced on progabide as compared with placebo (p <0.05). No drop‐outs owing to adverse effects were observed. In one case, somnolence required a reduction of the progabide dose. Somnolence (three cases), nausea or vomiting (two cases), and dysarthria (one case) were observed in six other patients on progabide but were judged to be mild. Laboratory tests did not show any treatment‐related alterations. Plasma concentrations of progabide measured before the morning dose ranged from <50 to 1,474 ng/ml. No correlation was found between plasma concentrations and the clinical outcome. In conclusion, results from this study indicate that progabide is well tolerated and possesses a promising antiepileptic activity in both partial and generalized epilepsies.

Spasm of the sternocleidomastoid muscle induced by vagal nerve stimulation

Vagal nerve stimulation (VNS) is a recently introduced treatment for drug-resistant epilepsies.1 Both partial and generalized seizures, especially atonic, may improve with this device, although the mechanism of action is not clearly understood. Approximately one third of patients treated with VNS have had a 50% reduction in the frequency of their seizures, thus making a significant impact on their quality of life.1 Efficacy has been related to the intensity of the stimulation. Side effects are generally infrequent and mild. They may be produced by the stimulation or the implant procedure. Voice alteration, hoarseness, dysphonia, cough, pain, dyspnea, vomiting, nausea, hiccups, paresthesia, fever, local infection, accidental injury, aspiration, and bradycardia have been quoted as side effects.1-3⇓⇓ Bradycardia is avoided by placing the stimulator by the left vagal nerve; however, even with this precaution, asystolia has been reported.4,5⇓ These complications usually did not lead to termination of the therapy. The occurrence of sudden death in these patients was not greater than in other epileptic patients.6 Overall, VNS treatment has proved to be safe, efficient, and cost-beneficial. A patient had a spasm of the sternocleidomastoid (SCM) when the stimulation intensity reached 2 mA. Clinically it was similar to an episodic torticollis. …

Independent component analysis separates spikes of different origin in the EEG.

Summary: Independent component analysis (ICA) is a novel system that finds independent sources in recorded signals. Its usefulness in separating epileptiform activity of different origin has not been determined. The goal of this study was to demonstrate that ICA is useful for separating different spikes using samples of EEG of patients with focal epilepsy. Digital EEG samples from four patients with focal epilepsy were included. The patients had temporal (n = 2), centrotemporal (n = 1) or frontal spikes (n = 1). Twenty-six samples with two (or more) spikes from two different patients were created. The selection of the two spikes for each mixed EEG was performed randomly, trying to have all the different combinations and rejecting the mixture of two spikes from the same patient. Two different examiners studied the EEGs using ICA with JADE paradigm in Matlab platform, trying to separate and to identify the spikes. They agreed in the correct separation of the spikes in 24 of the 26 samples, classifying the spikes as frontal, temporal or centrotemporal, left or right sided. The demonstration of the possibility of detecting different artificially mixed spikes confirms that ICA may be useful in separating spikes or other elements in real EEGs.

Sleep structure in patients with periodic limb movements and obstructive sleep apnea syndrome.

Abstract: Periodic limb movements (PLM) and obstructive sleep apnea syndrome (OSAS) are two frequent sleep disorders which often occur in the same patient. The goal of this study was to know the influence of the presence of PLM in the sleep architecture in patients with and without OSAS. Two hundred twenty consecutive patients (69 women and 151 men) participated in this transversal study. They were patients with clinical suspicion of dysomnia, including snoring, OSAS, and PLM. All of them underwent a full polysomnography and were interviewed using questionnaires about the sleep quality. The sleep parameters (percentage of sleep stages, rapid eye movement latency, sleep efficiency, awakenings, PLM presence, apnea-hypopnea index) were calculated and compared between groups. Descriptive statistics and nonparametric distribution techniques were used for the analysis. Patients with PLM when compared with patients with OSAS had lower sleep efficiency and less rapid eye movement percentage. The presence of PLM in patients with sleep apnea was less relevant being responsible only for an increase in the rapid eye movement latency and a decrease in the duration of the three to four sleep stages. However, the presence of OSAS was related to a better sleep efficiency (patients with PLM plus OSAS had a better sleep efficiency than patients with only PLM). PLM alters the structure of sleep. In patients with sleep apnea, the presence of PLM is less relevant.

Independent component analysis in the study of focal seizures.

Independent component analysis (ICA) is a novel technique that can separate statistically independent elements from complex signals. It has demonstrated its utility in separating artifacts and analyzing interictal discharges in EEG. ICA has been used recently in ictal recordings, showing the possibility of isolating the ictal activity. The goal of our study was to analyze focal seizures with ICA, decomposing the elements of the seizures to understand their genesis and propagation, and to differentiate between various types of focal seizures. We studied 26 focal seizures of temporal, frontal, or parietal origin. Only seizures with suspected focal onset were included in the study. The EEG recordings were acquired by using standard video-EEG equipment, with scalp electrodes. All the off-line analysis was carried out on a PC by means of specific software developed in the Matlab environment. ICA components were calculated with the use of the JADE (Joint Approximate Diagonalization of Eigen-matrices) algorithm. The decomposition of the seizures varied according to the EEG seizure pattern. In the seizures with focal rhythmic theta slow or sharp waves, the rhythmic activity was separated into one to five components, having an initial component with a clear concordance with the focus, whereas the others had an onset a few milliseconds later and corresponded to neighboring areas. In the 6 frontal seizures with regional rhythmic low voltage fast activity, 4 to 10 components were found, practically with a simultaneous timing, having a frontal distribution. In the three frontal seizures with a diffuse attenuation of the EEG signal, it was not possible to differentiate components of cerebral origin from the components of muscle artifact. ICA is an interesting tool to study the nature of focal seizures. The results depend on the EEG pattern. In the seizures with a clear EEG focal pattern, ICA may be useful to separate components of the ictal onset from the propagated activity.

Recognition of facial emotions and identity in patients with mesial temporal lobe and idiopathic generalized epilepsy: An eye-tracking study

PURPOSE To describe visual scanning pattern for facial identity recognition (FIR) and emotion recognition (FER) in patients with idiopathic generalized (IGE) and mesial temporal lobe epilepsy (MTLE). Secondary endpoint was to correlate the results with cognitive function. METHODS Benton Facial Recognition Test (BFRT) and Ekman&Friesen series were performed for FIR and FER respectively in 23 controls, 20 IGE and 19 MTLE patients. Eye movements were recorded by a Hi-Speed eye-tracker system. Neuropsychological tools explored cognitive function. RESULTS Correct FIR rate was 78% in controls, 70.7% in IGE and 67.4% (p=0.009) in MTLE patients. FER hits reached 82.7% in controls, 74.3% in IGE (p=0.006) and 73.4% in MTLE (p=0.002) groups. IGE patients failed in disgust (p=0.005) and MTLE ones in fear (p=0.009) and disgust (p=0.03). FER correlated with neuropsychological scores, particularly verbal fluency (r=0.542, p<0.001). Eye-tracking revealed that controls scanned faces more diffusely than IGE and MTLE patients for FIR, who tended to top facial areas. A longer scanning of the top facial area was found in the three groups for FER. Gap between top and bottom facial region fixation time decreased in MTLE patients, with more but shorter fixations in bottom facial region. However, none of these findings were statistically significant. CONCLUSION FIR was impaired in MTLE patients, and FER in both IGE and MTLE, particularly for fear and disgust. Although not statistically significant, those with impaired FER tended to perform more diffuse eye-tracking over the faces and have cognitive dysfunction.

Clinical phenotypes within non-surgical patients with mesial temporal lobe epilepsy caused by hippocampal sclerosis based on response to antiepileptic drugs

PURPOSE To evaluate evolution and elucidate clinical phenotypes related to prognosis of patients with mesial temporal lobe epilepsy related to hippocampal sclerosis (MTLE-HS) treated exclusively with antiepileptic drugs (AED). METHODS Forty-seven out of 68 MTLE-HS patients treated between January 2005 and June 2010 were retrospectively studied for demographic, clinical and outcome data. The population was divided into drug-responder and drug-resistant patients; the latter was divided, according to the duration of the seizure-free periods along their evolution, into patients with at least one seizure-free period longer than one year and those with shorter periods. Variables were compared between drug-responders vs drug-resistants and drug-resistants with long seizure-free periods vs drug-resistants without it. RESULTS There were 7 (15%) drug-responders, 39 (83%) drug-resistants and 1 patient (2%) with an undetermined response. Eighteen (46%) drug-resistant individuals had seizure-free periods longer than one year, with mean duration of 46 months (3.8 years). Since no factor was statistically associated with long seizure-free period within drug-resistants, we can clinically distinguish two phenotypes: women with left HS and late onset of seizures, with poor prognosis, and men with right HS and earlier appearance of seizures, attaining a better outcome. Twenty out of 47 (42.5%) patients followed an intermittent pattern of epilepsy. CONCLUSIONS Non-surgical MTLE-HS drug-resistant patients can achieve long seizure-free periods with AED, but relapses are common. Female gender, left or bilateral lesion and later onset of seizures seem to be bad prognosis factors within MTLE-HS drug-resistant patients.