Postural change in convulsive seizures: a retrospective review of video-electroencephalographic recordings.

BACKGROUND: Prone position has been identified as an important risk factor for sudden unexpected death in epilepsy raising the possibility of avoidance of this posture in sleep as a preventative measure. AIMS: To evaluate the potential utility of prone posture position, we studied patterns of postural change during generalised tonic clonic seizures. METHODS: Video-electroencephalographic recordings of patients undergoing investigations at the Royal Brisbane and Women's Hospital between 2005 and 2013 were reviewed independently by two raters. Head and truncal positions (left and right lateral, supine, sitting, prone) at seizure onset and offset, before and after nurse interventions were recorded. Post-ictal postural changes and evidence of stertorous respirations were also recorded. RESULTS: Thirty-one seizures from 27 patients were included in the study. One seizure began with the patient asleep in the prone position. One patient became prone during a seizure, having previously been asleep in the left lateral position. Nine patients changed position during a seizure. Seven of these patients were sitting or in a lateral position at the time of seizure onset, two patients were supine at seizure onset. No patient rolled by more than 90° during a seizure. Post-ictal stertorous respirations were observed in 14 patients, one of whom was prone. CONCLUSION: The incidence of patients attaining a prone position during a seizure was low. Given that no patient rolled more than 90°, patients are least likely to attain a prone position if they are supine at the beginning of a seizure.

Spikes with and without concurrent high-frequency oscillations: Topographic relationship and neural correlates using EEG-fMRI.

OBJECTIVE: Epilepsy surgery is the best therapeutic option for patients with drug-resistant focal epilepsy. During presurgical investigation, interictal spikes can provide important information on eligibility, lateralisation and localisation of the surgical target. However, their relationship to epileptogenic tissue is variable. Interictal spikes with concurrent high-frequency oscillations (HFOs) have been postulated to reflect epileptogenic tissue more reliably. Here, we studied the voltage distribution of scalp-recorded spikes with and without concurrent HFO and identified their respective haemodynamic correlates using simultaneous electroencephalography and functional Magnetic Resonance Imaging (EEG-fMRI). METHODS: The scalp topography of spikes with and without concurrent HFOs were assessed in 31 consecutive patients with focal drug-resistant epilepsy who showed interictal spikes during presurgical evaluation. Simultaneous EEG-fMRI was then used in 17 patients with spikes and concurrent HFOs. Haemodynamic changes were obtained from the spatial correlation between the patient-specific voltage map of each spike population and the intra-scanner EEG. The haemodynamic response of spikes with and without HFOs were compared in terms of their spatial similarity, strength, the distance between activation peaks and concordance with interictal localisation. RESULTS: Twenty-five patients showed spikes with and without concurrent HFOs. Among patients with both types of spikes, most spikes were not associated with HFOs (p < 0.0001, Mann-Whitney test). Twenty of the 25 patients showed an average of 8 ± 6 (standard deviation) electrodes with significant voltage differences (p = 0.025, permutation test corrected for multiple comparisons) on scalp electrodes within and distant to the spike field. Comparing the haemodynamic response between both spike populations, we found no significant differences in the peak strength (p = 0.71, Mann-Whitney test), spatial distribution (p = 0.113, One-sample Wilcoxon test) and distance between activation peaks (p = 0.5, One-sample Wilcoxon test), with all peaks being co-localised in the same lobe. SIGNIFICANCE: Our data showed that spikes with and without HFOs have different scalp voltage distributions. However, when assessing the haemodynamic changes of each spike type, we found that both elicit similar haemodynamic changes and share high spatial similarity suggesting that the epileptic networks of spikes with and without HFOs have the same underlying neural substrate.

Effects of prolonged repetitive stimulation of median, ulnar and peroneal nerves.

It is important to know the effects of prolonged repetitive nerve stimulation (RNS) when it is used in neurophysiological studies. RNS with up to 100 supramaximal stimuli was given to the median, ulnar, and peroneal nerves of normal subjects and the ulnar nerves of subjects with early amyotrophic lateral sclerosis (ALS), recording evoked compound muscle action potentials (CMAPs). In all nerves, there was a decline in the CMAP area and a decrease in CMAP duration. For the peroneal nerve there was a decline in the CMAP amplitude, but a similar decline was not seen in the median or ulnar nerves. Cooling of the muscles resulted in decrement of both the amplitude and area with RNS. In ALS subjects, CMAP amplitude and area both declined after RNS of the ulnar nerve. In this study we describe the changes in CMAP with prolonged RNS among commonly tested normal nerves. Our findings have important implications with regard to RNS.

Functional connectivity of the irritative zone identified by electrical source imaging, and EEG-correlated fMRI analyses.

OBJECTIVE: The irritative zone - the area generating epileptic spikes - can be studied non-invasively during the interictal period using Electrical Source Imaging (ESI) and simultaneous electroencephalography-functional magnetic resonance imaging (EEG-fMRI). Although the techniques yield results which may overlap spatially, differences in spatial localization of the irritative zone within the same patient are consistently observed. To investigate this discrepancy, we used Blood Oxygenation Level Dependent (BOLD) functional connectivity measures to examine the underlying relationship between ESI and EEG-fMRI findings. METHODS: Fifteen patients (age 20-54), who underwent presurgical epilepsy investigation, were scanned using a single-session resting-state EEG-fMRI protocol. Structural MRI was used to obtain the electrode localisation of a high-density 64-channel EEG cap. Electrical generators of interictal epileptiform discharges were obtained using a distributed local autoregressive average (LAURA) algorithm as implemented in Cartool EEG software. BOLD activations were obtained using both spike-related and voltage-map EEG-fMRI analysis. The global maxima of each method were used to investigate the temporal relationship of BOLD time courses and to assess the spatial similarity using the Dice similarity index between functional connectivity maps. RESULTS: ESI, voltage-map and spike-related EEG-fMRI methods identified peaks in 15 (100%), 13 (67%) and 8 (53%) of the 15 patients, respectively. For all methods, maxima were localised within the same lobe, but differed in sub-lobar localisation, with a median distance of 22.8 mm between the highest peak for each method. The functional connectivity analysis showed that the temporal correlation between maxima only explained 38% of the variance between the time course of the BOLD response at the maxima. The mean Dice similarity index between seed-voxel functional connectivity maps showed poor spatial agreement. SIGNIFICANCE: Non-invasive methods for the localisation of the irritative zone have distinct spatial and temporal sensitivity to different aspects of the local cortical network involved in the generation of interictal epileptiform discharges.