Transcranial and direct cortical stimulation for motor evoked potential monitoring in intracerebral aneurysm surgery

STUDY AIM: To analyse the parallel use of transcranial electrical stimulation (TES) and direct cortical stimulation (DCS) for eliciting muscle motor evoked potentials (MMEPs) in intracranial aneurysm surgery; to correlate permanent or transient TES- and/or DCS-MMEP changes with surgical maneuvers and clinical motor outcome. PATIENTS AND METHODS: TES and DCS were intraoperatively performed in 108 patients (51.5+/-14.7 years); MMEPs were obtained in muscles belonging to the vascular territory of interest. Monopolar, anodal stimulation was achieved with a train of five stimuli consisting of an individual pulse width of 0.5ms, an interstimulus interval of 4ms, a train repetition rate of 0.5-2Hz, and maximum stimulation intensities up to 200mA (TES) versus 25mA (DCS). RESULTS: In 95/108 (88%) patients, no changes in MMEPs occurred and none of these patients suffered a permanent severe motor deficit. In 14/108 (12%) patients, we observed nine (64%) temporary changes, four (29%) permanent deteriorations and one (7%) permanent MMEP loss. Out of 14 MMEP changes, nine (64%) occurred with TES, compared to 13 (93%) with DCS (Fishers'p=0.165). Parallel changes in TES- and DCS-MMEPs occurred in 8/14 patients (57%), in which case a permanent loss was always followed by a permanent severe motor deficit. Sixty-seven percent of all permanent changes occurred with DCS-MMEPs, compared to 33% with TES-MMEPs (p=0.567, NS). DISCUSSION AND CONCLUSIONS: In aneurysm surgery, provided that close-to-motor-threshold stimulation and the most focal stimulating electrode montage are used, TES- and DCS-MMEPs do not differ in their capacity to detect an impending lesion of the motor cortex or its efferent pathways. TES stimulation can cause significant muscular contraction during surgery, potentially disrupting the operating surgeon. DCS maintains the singular advantage of stimulating a very focal and superficial motor cortex stimulation that does not result in patient movement.     

Dysphagia and hemispheric stroke: A transcranial magnetic study

INTRODUCTION: Dysphagia is a common and distressing consequence of hemispheric stroke. STUDY AIM: To verify the usefulness of transcranial magnetic stimulation (TMS) studies of swallowing in healthy subjects and in stroke patients. MATERIAL AND METHODS: TMS studies of the motor cortical projections to the upper esophageal sphincter were performed in 45 patients with acute mono-hemispheric stroke (26 patients with dysphagia) and 20 healthy adult volunteers. RESULTS: TMS of either hemisphere in normal volunteers evoked motor evoked potentials (MEP) in the esophagus. The average point of optimal excitability was slightly more anterior in the right hemisphere; otherwise, MEP amplitudes and latencies were similar from both hemispheres as were the areas of the cortical map. The cortical map area and amplitude of MEPs were significantly smaller and the latencies longer after stimulation of the affected hemisphere compared with the unaffected hemisphere and pooled control data. Twenty-four dysphagic patients (92.3%) had abnormalities of MEP of the affected hemisphere, while only five non-dysphagic patients (26%) had these abnormalities. Dysphagic patients were older and had more disability compared with non-dysphagic patients. MEPs of the affected hemisphere of patients with dysphagia were later and smaller in amplitude than MEPs of non-dysphagic patients. The cortical map area was also smaller. CONCLUSION: The esophagus is represented bilaterally in motor cortex, but the hot spot lies more anterior to Cz in right hemisphere compared to left hemisphere. Both the severity of stroke and neuroplasticity of the unaffected hemisphere have implications in the development of dysphagia.     

Stroke prevention during surgery for deep-seated gliomas

AIMS OF THE STUDY: New motor deficit after surgery for deep-seated gliomas can occur from subcortical ischemia of the pyramidal tract. Motor evoked potentials (MEPs) validly indicate impending motor tract ischemia in cerebrovascular surgery. This study determines the feasibility and clinical utility of MEP monitoring for ischemic complication avoidance during surgery for deep-seated, specifically insular gliomas. METHODS: MEPs were recorded during 100 operations of insular gliomas. Intraoperative MEP results were correlated with postoperative clinical and imaging results. RESULTS: Useful MEP monitoring was possible in 89/100 cases, 88 of which were assessable since one patient died early postoperatively. Stable recordings warranted unimpaired motor outcome in 47/88 cases (53%). Surgical intervention reversed MEP attenuation in 26 of the remaining 41 cases (30% of the overall series) to prevent motor deficit except transient paresis in 12 (14%). Irreversible MEP changes without loss in eight cases (9%) resulted in only transient new deficit in seven cases, except one with permanent new paresis. Permanent paresis also occurred in seven cases (8%) where complete MEP loss could not be prevented. Permanent paresis arose exclusively through stroke of the deep motor pathways, whereas transient deficit typically corresponded to transitory ischemia of the pyramidal tract. MEP changes attributable to ischemic events frequently occurred spatially and temporally uncorrelated to resection in critical proximity of the motor tract. CONCLUSIONS: Ischemia in deep-seated glioma surgery usually occurs uncorrelated to resection close to the pyramidal tract. MEP monitoring efficiently helps detect ischemia early and to avert definite stroke and permanent new paresis in part of these cases.     

Subthalamic nucleus stimulation in Parkinson''s disease: Postoperative CT–MRI fusion images confirm accuracy of electrode placement using intraoperative multi-unit recording

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is increasingly used to treat advanced Parkinson's disease (PD). The optimal method for targeting the STN before implanting the definitive DBS electrode is still a matter of debates. Beside methods of direct visualization of the nucleus based on stereotactic magnetic resonance imaging (MRI), the most often used technique for targeting STN consists in recording single-cell activity along exploratory tracks of 10-15mm in length, centered on the theoretical or MRI-defined target coordinates. Single-unit recordings with a microelectrode present various drawbacks. They are time-consuming if correctly performed and a single-cell precision is probably superfluous, taking into account the size of the implanted electrode. In this study, we present an original method of recording and quantification of a multi-unit signal recorded intraoperatively with a semi-microelectrode for targeting the STN. Twelve patients with advanced PD have been included and assessed clinically before and one year after bilateral STN-DBS electrode implantation guided by multi-unit electrophysiological recordings. After one year of chronic stimulation, all patients showed a marked clinical improvement. The motor score of the unified Parkinson's disease rating scale decreased by more than 57% and the required levodopa-equivalent daily dose by 59.5% in on-stimulation off-medication condition compared to off-stimulation off-medication condition. The accuracy of STN-DBS lead placement was confirmed on postoperative computed tomography (CT) scans, which were fused to preoperative T2-weighted MRI. The boundaries of the STN were easily determined by an increase in multi-unit signal amplitude, which was observed on average from 0.492mm below the rostral border of the STN down to 0.325mm above its caudal border. Signal amplitude significantly increased at the both rostral and caudal STN margins (P<0.05) and the level of neuronal activity easily distinguished inside from outside the nucleus. This study showed that STN boundaries could be adequately determined on the basis of intraoperative multi-unit recording with a semi-microelectrode. The accuracy of our method used for positioning DBS electrodes into the STN was confirmed both on CT-MRI fusion images and on the rate of therapeutic efficacy.     

Infarctus cérébral récidivant révélant une maladie de Biermer

Introduction

Biermer's disease is an autoimmune disorder characterized by vitamin B12 deficiency. Ischemic stroke is an uncommon complication of Biermer's disease, possibly though hyperhomocysteinemia.

Case report

A 58-year-old male presented with recurrent ischemic stroke. Extensive investigations were normal, except for a high plasma level of homocysteine in the context of pernicious anemia which was otherwise asymptomatic.

Discussion

Hyperhomocysteinemia is a known marker, and probably a risk factor, for stroke, fostering atherosclerosis and thrombosis. It can be found among individuals suffering from homocysteinuria, but also when there is deficiency of vitamin B12 or folic acid. Vitamin B12 supplementation would reduce homocysteine concentration which in turn would reduce the risk of ischemic stroke.     

Monitoring of motor pathways during brain stem surgery: What we have achieved and what we still miss?

Intraoperative neurophysiological monitoring (IOM) has established itself as one of the paths by which modern neurosurgery can improve surgical results while minimizing morbidity. IOM consists of both monitoring (continuous "on-line" assessment of the functional integrity of neural pathways) and mapping (functional identification and preservation of anatomically ambiguous nervous tissue) techniques. In posterior-fossa and brainstem surgery, mapping techniques can be used to identify - and therefore preserve - cranial nerves, their motor nuclei and corticospinal or corticobulbar pathways. Similarly, free-running electromyography (EMG) and muscle motor-evoked potential (mMEP) monitoring can continuously assess the functional integrity of these pathways during surgery. Mapping of the corticospinal tract, at the level of the cerebral peduncle as well as mapping of the VII, IX-X and XII cranial nerve motor nuclei on the floor of the fourth ventricle, is of great value to identify "safe entry-zones" into the brainstem. Mapping techniques allow recognizing anatomical landmarks such as the facial colliculus, the hypoglosseal and glossopharyngeal triangles on the floor of the fourth ventricle, even when normal anatomy is distorted by a tumor. On the basis of neurophysiological mapping, specific patterns of motor cranial nuclei displacement can be recognized. However, brainstem mapping cannot detect injury to the supranuclear tracts originating in the motor cortex and ending on the cranial nerve motor nuclei. Therefore, monitoring techniques should be used. Standard techniques for continuously assessing the functional integrity of motor cranial nerves traditionally rely on the evaluation of spontaneous free-running EMG in muscles innervated by motor cranial nerves. Although several criteria have been proposed to identify those EMG activity patterns that are suspicious for nerve injury, the terminology remains somewhat confusing and convincing data regarding a clinical correlation between EMG activity and clinical outcome are still lacking. Transcranial mMEPs are also currently used during posterior-fossa surgery and principles of MEP monitoring to assess the functional integrity of motor pathways are similar to those used in brain and spinal-cord surgery. Recently, current concepts in muscle MEP monitoring have been extended to the monitoring of motor cranial nerves. So-called "corticobulbar mMEPs" can be used to monitor the functional integrity of corticobulbar tracts from the cortex through the cranial motor nuclei and to the muscle innervated by cranial nerves. Methodology for this purpose has appeared in the literature only recently and mostly with regards to the VII cranial nerve monitoring. Nevertheless, this technique has not yet been standardized and some limitations still exist. In particular, with regards to the preservation of the swallowing and coughing reflexes, available intraoperative techniques are insufficient to provide reliable prognostic data since only the efferent arc of the reflex can be tested.     

Conditioning stimulation techniques for enhancement of transcranially elicited evoked motor responses

INTRODUCTION: In spite of the use of multipulse, transcranial electrical stimulation (TES) is still insufficient in a subgroup of patients to elicit motor-evoked potentials during intraoperative neurophysiological monitoring (IONM). Classic facilitation methods used in awake patients are precluded under general anaesthesia. Conditioning techniques can be used in this situation. OBJECTIVE: To present clinical experimental data and models of motor-neuron (MN) excitability for homonymous and heteronymous conditioning and discuss their applications in IONM. MATERIAL AND METHODS: Data were obtained in a prospective study on multipulse TES-conditioning of the monosynaptic H-reflex and double multipulse TES. DISCUSSION: The principle of facilitation by conditioning stimulation is to apply a test stimulus when motor neurons (MNs) have been made maximally excitable by a conditioning stimulus. Both conditioning and test stimuli recruit separate populations of MNs. The overlapping fraction of MNs controls the efficacy of facilitation. Heteronymous conditioning stimulation, which is performed at a different site from the test stimulus, is illustrated by the TES-conditioned H-reflex (HR). Autonomous conditioning stimulation, which is performed at the same stimulation site, is illustrated by double-train TES (dt-TES). The facilitating curves obtained by conditioning stimulation are often 3-modal and show peaks of facilitation at short intertrain intervals (S-ITIs) of 10ms and between 15 and 20ms and at longer intertrain intervals (L-ITI) of over 100ms. The facilitation curves from HR and dt-TES are not always identical since different alphaMN pools are involved. Dt-TES is often successful in neurologically impaired patients whereas facilitation of the HR can be used when conditioned by TES at subthreshold levels allowing continuous IONM without movement in the surgical field. Alternatively, facilitation by conditioning from peripheral-nerve stimulation can be used for selective transmission of subthreshold TES motor responses to peripheral muscles, permitting motor-monitoring by a so-called selective motor-gating technique. CONCLUSIONS: Facilitation techniques offer many possibilities in IONM by enhancing low-amplitude TES-MEP responses. They can also selectively enhance responses in a few muscle groups for the reduction of movement.     

Criteria for transcranial electrical motor evoked potential monitoring during spinal deformity surgery: A review and discussion of the literature

Transcranial electrical stimulated motor evoked potential monitoring (TES-MEP) has proven to be a successful and reliable neuromonitoring technique during spinal correction surgery. However, three criteria for TES-MEP monitoring have been described in the literature. This study aims at discussing and comparing the following criteria: (1) the "threshold level criterion" introduced by Calancie et al. (J Neurosurg 88 (1998) 457-70): a more than 100V over more than 1h increase of threshold level to get useful TES-MEP responses indicated neurological impairment; (2) the "amplitude criterion": for TES-MEP monitoring in corrective surgery of the spine, a more than 80% decrease of one or more response amplitudes was considered a valuable criterion for impending neurological deficits by Langeloo et al. (Spine 28 (2003) 1043-50); (3) "the morphology criterion": introduced in 2005 by Quinones et al. (Neurosurgery 56 (2005) 982-93), it is based on the morphology of the MEP-compound muscle action potentials (CMAP). The criterion was applied during TES-MEP monitoring during intramedullary spinal cord tumour resection. Neurological events are defined by a sharp decrease of response duration and/or waveform complexity and an increase in voltage threshold of 100V or greater. Although all methods have been reported to be successful during spinal surgery, the threshold criterion and the morphology change criterion carry several drawbacks. We consider the amplitude reduction method to be most useful during corrective spinal surgery. The sequences of observations and decisions during a TES-MEP monitoring that is based on this criterion are schematized in a flowchart.     

What is “mirror” in the premotor cortex? A review

We review the findings of 24 fMRI studies examining activations in the premotor cortex (Brodmann's areas 6 and 44) during passive observation of actions. We found that such activations regularly occurred. Looking for functional differentiation in the premotor cortex, we found that one parameter was associated with systematic differences in location: this was the presence or absence of targets. Observing biological actions with a physical target, compared to a visual control showing no action at all, consistently activated the ventral premotor cortex (BA 6), and did so significantly more than observing target-less actions (with the same control). In contrast, the activity in BA 44 ("Broca's area") was not modulated by the presence or absence of targets. We propose that the ventral precentral gyrus, and not BA 44, shares the visual properties of "mirror" neurons found in area F5 of the macaque brain.     

Paradigm design of sensory–motor and language tests in clinical fMRI

Functional magnetic resonance imaging (fMRI) paradigms on sensory-motor and language functions are reviewed from a clinical user's perspective. The objective was to identify special requirements regarding the design of fMRI paradigms for clinical applications. A wide range of methods for setting up fMRI examinations were found in the literature. It was concluded that there is a need for standardised procedures adapted for clinical settings. Sensory-motor activation patterns do not vary much at different hand motion tasks. Nevertheless it is one of the most important clinical tests. In contrast, the language system is much more complex. In several studies it has been observed that word production tasks are preferable in determination of language lateralisation. Broca's area is activated by most tasks, whereas sentence processing and semantic decision also involve activation in temporoparietal and frontal areas. However, combined task analysis (CTA) of several different tasks has been found to be more robust and reliable for clinical fMRI compared to separate task analysis.     

Newborns with hyperbilirubinemia: usefulness of brain stem auditory response evaluation

We describe brain stem auditory evoked potentials (BAEP) obtained in 48 full-term newborns (20 boys, 28 girls) presenting with high serum total bilirubin concentration (from 238 to 442 mM) without Rhesus or group A, B, O factors incompatibility. Recordings were performed on the 3rd day of life and repeated 5–7 days post-appropriate therapy with photostimulation and exchange transfusion (when bilirubin concentration had decreased below 136 mM). Supplementary recordings were performed 3, 6 and 12 weeks later in order to assess test-retest reliability of components. Mean values of BAEP latencies were compared with those obtained in 40 age-matched control subjects using the same recording procedures. At first recording session (on the 3rd day), latencies of waves III and V obtained in hyperbilirubinemic patients were significantly increased as compared with records in control subjects. Recordings performed 5 to 7 days post-therapy and during subsequent recording sessions showed no significant differences between patients and control groups. Serial neuropsychological evaluations obtained over a 3-year follow-up showed no subsequent neurodevelopmental abnormality for all patients. These findings suggest that hyperbilirubinemia can alter central neurotransmission in auditory brain stem pathways, but this modification is only transient.

Résumé

Nous avons enregistré les potentiels évoqués auditifs du tronc cérébral (brain stem auditory evoked potentials, BAEP) de 48 nouveau-nés (20 garçons, 28 filles). Les sujets avaient une concentration sanguine élevée en bilirubine totale (de 238 à 442 mM) et ne présentaient ni incompatibilité du facteur rhésus, ni incompatibilité de groupe sanguin (A, B, O). Les enregistrements ont été effectués au 3^e jour de vie, puis répétés aux 5^e et 7^e jours de vie après traitement par photostimulation et exsanguinotransfusion (lorsque la concentration de bilirubine était inférieure à 136 mM). Des enregistrements effectués 3, 6 et 12 semaines plus tard ont permis de vérifier la reproductibilité des BAEP. Les valeurs moyennes des latences des BAEP ont été comparées à celles obtenues dans un groupe témoin de 40 sujets. Au cours de la première évaluation, les latences de la 3^e et de la 5^e onde enregistrées chez les enfants présentant une hyperbilirubinémie étaient plus élevées que chez les sujets témoins. Les enregistrements effectués par la suite ont montré que les latences des composantes des BAEP étaient identiques dans les deux groupes. Les évaluations effectuées au cours des trois années suivantes ont mis en évidence l'absence de désordres neuropsychologiques. Cette étude montre que l'hyperbilirubinémie peut modifier la neurotransmission centrale, mais uniquement de façon transitoire.     

Acute motor conduction block neuropathy pattern occurring in the course of an acute inflammatory demyelinating polyradiculoneuropathy

OBJECTIVE: To describe the case of a young woman with the diagnosis of acute inflammatory demyelinating polyradiculoneuropathy (AIDP), who during the course of the disease developed an electrophysiologic pattern of acute motor conduction block neuropathy (AMCBN). METHODS: Electrophysiologic techniques including needle EMG, standard motor and sensory nerve conductions studies, and somatosensory evoked potentials were carried out over the four months after symptom onset. RESULTS: The results of four neurophysiological studies, performed on Days 14, 26, 35 and 125 after symptomatic onset are reported. All immunological determinations including antiganglioside antibodies (GM1, GM2, GM3, asialoGM1, GD1a, GD1b, GD3, GQ1b and GT1b) were negative. The patient had a favorable evolution following treatment with intravenous immunoglobulins (IVIg). CONCLUSIONS: We conclude that the electrophysiologic hallmark of AMCBN may occur in the course of AIDP. Serial investigation including proximal, intermediate and distal segments of all nerves from upper and lower limbs is essential for its detection.     

Autobiographic memory: Phenomenological aspects, personal semantic knowledge, generic events and characters (one case of pure retrograde memory recovery)

Tulving et al. [Brain Cogn 8 (1988) 3-20] proposed an operational distinction concerning memory between a semantic component consisting of general information about the individual's past and an episodic component, containing memories of specific events that can be situated in space and time. After a mild head trauma and in the context of professional troubles, patient FF displayed a pure retrograde amnesia concerning both his biographical identity and semantic memories. The patient could no longer access his memories. However, these did not seem completely lost since his answers to tests concerning historical events were better than random, his answers to a television quiz were automatic, he showed temporal transfer phenomena (ecmnesia) and since he retrieved the entirety of his memories within nine months. The patient FF illustrates the loss of retrograde autobiographic memory and the recovery of episodic memories, which requires three elements: a sense of subjective time, an autonoetic awareness (the ability to be aware of subjective time) and a "self" that can travel in subjective time.     

An odd manifestation of the Capgras syndrome: Loss of familiarity even with the sexual partner

We report the case of a patient who presented visual hallucinations and identification disorders associated with a Capgras syndrome. During the Capgras periods, there was not only a misidentification of his wife's face, but also a more global perceptive and emotional sexual identification disorder. Thus, he had sexual intercourse with his wife's "double" without having the slightest recollection feeling of familiarity towards his "wife" and even changed his sexual habits. To the best of our knowledge, he is the only neurological patient who made his wife a mistress. Starting from this global familiarity loss, we discuss the mechanism of Capgras delusion with reference to the role of the implicit system of face recognition. Such behavior of familiarity loss not only with face but also with all intimacy aspects argues for a specific disconnection between the ventral visual pathway of face identification and the limbic system involved in emotional and episodic memory contents.