Clinico-electroencephalographic correlation for levels of consciousness: Systematic EEG adds value to exam and imaging in tripod neurologic assessment (original) (raw)
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Significance of cathodal stimulation for motor evoked potential monitoring
The Kitasato medical journal, 2017
Objective: Intraoperative motor evoked potential (MEP) monitoring is essential to reduce the risk of neurosurgical procedures damaging the motor system. The standard technique of recording MEP uses high-frequency anodal monopolar stimulation of the primary motor cortex. The present study investigated the possibility that cathodal stimulation allows MEP recording at lower intensities than does anodal stimulation in certain patients. Methods: Motor threshold (MT) was measured and compared for anodal and cathodal stimulation in 65 patients in Kitasato University Hospital. The patients were divided into 3 groups based on the polarity of the lower MT: anodal less than cathodal stimulation (Group A), cathodal less than anodal stimulation (Group B), and anodal similar to cathodal stimulation (Group C). Magnetic resonance (MR) imaging findings of hyperintensity extending to the precentral knob accompanied by brain tumor were evaluated to correlate with the polarity of lower MT. Results: The...
2014
In the present study, we aimed to detect the ”resonance-like” frequencies of the somatosensory system in patients in a minimally conscious state using a screening paradigm. EEG measurements were conducted in seven patients during tactile stimulation of their left and right wrist. A significant tuning curve could be found in one of the patients. Various reasons that could explain the inconclusive outcome of most measurements, as well as future perspectives are discussed.
Annales Françaises d'Anesthésie et de Réanimation, 2014
Six clinical studies of chronic electrical modulation of deep brain circuits published between 1968 and 2010 have reported effects in 55 vegetative or minimally conscious patients. The rationale stimulation was to activate the cortex through the reticular-thalamic complex, comprising the tegmental ascending reticular activating system and its thalamic targets. The most frequent intended target was the central intralaminar zone and adjacent nuclei. Hassler et al. also proposed to modulate the pallidum as part of the arousal and wakefulness system. Stimulation frequency varied from 8 Hz to 250 Hz. Most patients improved, although in a limited way. Schiff et al. found correlations between central thalamus stimulation and arousal and conscious behaviours. Other treatments that have offered some clinical benefit include drugs, repetitive magnetic transcranial stimulation, median nerve stimulation, stimulation of dorsal column of the upper cervical spinal cord, and stimulation of the fronto-parietal cortex. No one treatment has emerged as a gold standard for practice, which is why clinical trials are still ongoing. Further clinical studies are needed to decipher the altered dynamics of neuronal network circuits in patients suffering from severe disorders of consciousness as a step towards novel therapeutic strategies. Résumé Six études cliniques de modulation électrique chronique de circuits cérébraux profonds, publiées entre 1968 et 2010, ont rapporté des effets chez 55 patients, végétatifs ou en état de conscience minimale. Le rationnel de stimulation était d'activer le cortex par le complexe réticulo-thalamique comprenant le système réticulaire activateur ascendant tegmental et ses cibles thalamiques. La cible la plus fréquemment visée était la zone centrale intra laminaire du thalamus et les noyaux adjacents. Hassler et al. ont aussi proposé de moduler le pallidum, partie du système d'éveil et de vigilance. La fréquence de stimulation variait de 8 Hz à 250 Hz. La plupart des patients se sont améliorés, bien que de manière limitée. Schiff et al. ont démontré un lien entre l'apparition de comportements d'éveil et conscients et stimulation du thalamus central. D'autres traitements ont pu améliorer cliniquement le patient : médicaments, stimulation magnétique transcrânienne répétée, stimulation du nerf médian, stimulation des cordons postérieurs de la moelle cervicale et stimulation du cortex frontopariétal. Aucun traitement n'a été validé pour la clinique courante, d'où la réalisation d'études cliniques, enregistrées, en cours. De nouvelles études sont nécessaires pour décrypter les altérations de la dynamique des circuits neuronaux chez des patients souffrant de troubles de la conscience sévères, permettant ainsi de proposer de nouvelles stratégies thérapeutiques.
Frontiers in Neuroscience, 2020
A severe brain injury may lead to a disorder of consciousness (DOC) such as coma, vegetative state (VS), minimally conscious state (MCS) or locked-in syndrome (LIS). Till date, the diagnosis of DOC relies only on clinical evaluation or subjective scoring systems such as Glasgow coma scale, which fails to detect subtle changes and thereby results in diagnostic errors. The high rate of misdiagnosis and inability to predict the recovery of consciousness for DOC patients have created a huge research interest in the assessment of consciousness. Researchers have explored the use of various stimulation and neuroimaging techniques to improve the diagnosis. In this article, we present the important findings of resting-state as well as sensory stimulation methods and highlight the stimuli proven to be successful in the assessment of consciousness. Primarily, we review the literature based on (a) application/non-use of stimuli (i.e., sensory stimulation/resting state-based), (b) type of stimulation used (i.e., auditory, visual, tactile, olfactory, or mental-imagery), (c) electrophysiological signal used (EEG/ERP, fMRI, PET, EMG, SCL, or ECG). Among the sensory stimulation methods, auditory stimulation has been extensively used, since it is easier to conduct for these patients. Olfactory and tactile stimulation have been less explored and need further research. Emotionally charged stimuli such as subject's own name or narratives in a familiar voice or subject's own face/family pictures or music result in stronger responses than neutral stimuli. Studies based on resting state analysis have employed measures like complexity, power spectral features, entropy and functional connectivity patterns to distinguish between the VS and MCS patients. Resting-state EEG and fMRI are the state-of-theart techniques and have a huge potential in predicting the recovery of coma patients. Further, EMG and mental-imagery based studies attempt to obtain volitional responses from the VS patients and thus could detect their command-following capability. This may provide an effective means to communicate with these patients. Recent studies have employed fMRI and PET to understand the brain-activation patterns corresponding to the mental imagery. This review promotes our knowledge about the techniques used for the diagnosis of patients with DOC and attempts to provide ideas for future research.
Journal of Neurology, Neurosurgery & Psychiatry, 1992
Central sensory and motor conduction were studied in 23 comatose and three brain-dead patients. Motor evoked potentials (MEPs) to transcranial magnetic (magMEP) and electrical (elMEP) stimulation were recorded from the hypothenar muscle, and somatosensory evoked potentials (SEPs) were recorded after median nerve stimulation. Comparison of clinical with evoked potential (EP) findings revealed: 1) a painful stimulus applied to the skin of the arm lowered excitation threshold to cortical stimulation and was a prerequisite to obtain MEPs in 14 instances; 2) only in braindead patients were all EPs abolished simultaneously and bilaterally; 3) MEPs
British Journal of Anaesthesia, 2008
Background. We investigated the relationship between median nerve somatosensory evoked potentials (SSEPs) and the bispectral index (BIS) during alternating periods of consciousness and propofol-induced unconsciousness. Methods. Loss of consciousness (LOC) was repetitively induced by bolus injections of propofol in 24 patients undergoing elective surgery in spinal anaesthesia. SSEP and the BIS were recorded during LOC and recovery of consciousness (ROC). The level of consciousness was clinically assessed by the observer's assessment of alertness/sedation scale. Propofol venous plasma concentrations were measured simultaneously. Results. At LOC, all SSEPs latency components were prolonged (P,0.001), whereas amplitudes of the components !45 ms were smaller (P¼0.008) and the BIS values were lower (P,0.001). None of the EEG variables regained baseline levels during ROC. Regression analyses revealed that the SSEP components (five latencies and five amplitudes) explained 33% of the variance when predicting ROC; the BIS explained 12%. The combination of SSEP and BIS explained 37% of variance in this patient sample. Propofol venous plasma concentration was 1.2 (0.8) mg ml 21 during LOC and 0.4 (0.5) mg ml 21 during ROC. Conclusions. The present results indicate the usefulness of combining variables of the evoked and spontaneous EEG to measure different levels of consciousness, because the SSEP provide additional information beyond the BIS. Inter-individual variability of all the EEG variables limits their predictive potency of ROC after propofol infusion.