Magnetic evoked potentials in neurocritical care patients with acute brainstem lesions

OBJECTIVES: Motor evoked potentials (MEPs) are widely used in various neurological diseases, but have not been systematically employed in neurocritical care patients. We evaluated the clinical and predictive value of MEPs by magnetic transcranial stimulation in intensive care patients with acute brainstem lesions of predominantly vascular origin. METHODS: In a prospective trial, a total of 30 patients with acute brainstem lesions were studied. Diagnoses were brainstem infarction (n=15), brainstem hemorrhage (n=3), encephalitis (n=1), basilar artery aneurysm (n=1), and space-occupying cerebellar infarct (n=5), cerebellar hemorrhage (n=3), and brainstem contusion (n=2). We performed MEP tests by transcranial stimulation to the abductor pollicis brevis bilaterally, bilateral somatosensory (SEPs) and auditory evoked (BAEPs) potentials. We determined motor function at the time of electrophysiological testing and after 3 months, the presence of radiologically confirmed lesions, and clinical outcome after 3 months. At the time of MEP recordings, ten patients were comatose, twelve stuporous, seven somnolent and one awake. RESULTS: MEPs were present bilaterally in seventeen, absent unilaterally in eight and bilateral absent in five patients. Absent MEP highly correlated with the presence of persisting motor deficit 3 months later (P<0.0001). Absent MEPs predicted motor deficit after 3 months with a high specificity and more precisely than the clinical examination at the time of MEP testing. MEP findings correlated with the presence of radiologically confirmed lesions within the brainstem (P<0.0001). Combined with SEP and BAEP data, MEPs predicted the presence of unilateral brainstem lesions with high accuracy. CONCLUSIONS: MEP recordings can be safely performed in neurointensive care patients and yield utilizable results. In patients with brainstem lesions, MEPs correlate with radiological findings and predict final motor function more accurately than clinical findings. MEPs are a reliable diagnostic tool for assessing motor function in otherwise unresponsive patients.     

The usefulness of EEG, exogenous evoked potentials, and cognitive evoked potentials in the acute stage of post-anoxic and post-traumatic coma

Three-modality evoked potentials (TMEPs) have been used for several years in association with the EEG as a diagnostic and prognostic tool in acute anoxic or traumatic coma. Cognitive EPs have been recently introduced. EEG and cognitive EPs provide functional assessment of the cerebral cortex. TMEP parameters can be described by two indices: the index of global cortical function (IGCF) and the index of brainstem conduction (IBSC). Although it remains a unique tool for epilepsy assessment, the value of EEG is largely limited by its high sensitivity to the electrical environmental noise, its dependence on sedative drugs, and its inability to test the brainstem. Major TMEP alterations (absence of cortical activities more than 24 hours after the onset of post-anoxic coma, major pontine involvement in head trauma) are associated in all cases with an ominous prognosis (death or vegetative state). However, even if mild TMEP changes are associated with a good prognosis in 65% (post-anoxic coma) to 90% (head trauma) of cases, some patients never recover despite exogenous TMEPs that are only mildly altered in the acute stage. Thus, cognitive EPs can usefully complement exogenous EPs as a prognostic tool in coma. Indeed, even if the absence of cognitive EPs in comatose patients does not have any prognostic value, their presence implies a very high (more than 90%) probability of consciousness recovery. The major technical challenge for the future will be the development of reliable tools for continuous EEG and TMEP monitoring.     

Somatosensory and brainstem auditory evoked potential studies in nontraumatic coma

We believe that somatosensory and brainstem auditory evoked response studies help in the understanding of the dysfunction of the ascending sensory pathyways at various levels. In some patients where EEGs showed a significant contamination of muscle and background noise, the SEP studies helped to identify the level of dysfunction. The severity of the clinical condition (GCS score) correlated significantly (p = 0.003) with the prolongation of the CCT. Asymmetries in CCTs were more frequent in the stroke group than in the other groups. The presence of asymmetries in CCT in diffuse encephalopathies indicated a variable degree of dysfunction in the ascending sensory pathways, which clinically were not easily identifiable. This fact raised the possibility of either pre-existing lesion(s) or recent insult(s) such as ischemia. The presence or absence of N20 appeared to influence the duration of survival in subgroups. Some degree of difference in duration of survival was noted among the metabolic group with and without N20 potential. The subset of patients with N20 potential survived relatively longer than the group without it. A suggestion of influence was seen in the stroke group, but caution must be exercised because the absence of N20 was compatible with survival. The hypoxic group did not show any difference. A combination of prolonged interpeak EP-N13 and N13-N20 indicated a poor prognosis. A distinct absence of Wave I in BAER limited its usefulness on some occasions. A combination of abnormal interpeak III-V and abnormal CCT seemed to suggest a poor prognosis. Although death generally occurred earlier in the stroke group, age did not seem to influence the mortality in the first 10 days. Similarly, the cause of death also did not seem to influence the course in those 10 days. None of the adult patients survived.     

脑干及其附近手术诱发电位术中监护的研究

目的 探讨脑干及其周围手术损伤与脑干听觉诱发电位（ＢＡＥＰ）和体感诱发电位（ＳＥＰ）不同指标之间的关系,找出神经功能损伤第三的电生理指标。方法 对２３例脑干肿瘤病人进行手术中ＢＡＥＰ和ＳＥＰ连续监测。结果 脑干及其周围手术操作均可以引起ＢＡＥＰ、ＳＥＰ的改变。ＳＥＰ的Ｎ１３－Ｎ２０中枢传导时间（ＣＣＴ）和Ｎ２０潜伏期及波幅的变化和ＢＡＥＰＶ波潜伏期（ＰＬ）、Ⅲ－Ｖ、Ｉ－Ｖ峰间潜伏期（ＩＰＬ）的变化     

Auditory brainstem evoked potentials in early-treated congenital hypothyroidism

To evaluate the effect of early treatment of congenital hypothyroidism on central nervous system development, auditory brainstem evoked potentials were determined in 32 patients with hyperthyrotropinemia diagnosed during neonatal screening. The patients included 27 with congenital hypothyroidism and 5 with transient hypothyroidism. Abnormal auditory brainstem evoked potential tracings were found in 8 patients (congenital hypothyroidism in 7 and transient hypothyroidism in 1). Four of these patients had increased peripheral conduction time (wave I prolongation), and the other 4 had increased central conduction time (wave III or V prolongation). The patients with abnormal auditory brainstem evoked potentials did not show increased initial manifestations, yet 6 of them had lower initial thyroxine levels. Specific auditory brainstem evoked potential abnormalities were found in 25% of early-treated patients with congenital hypothyroidism. The possible causal relationship between deviant auditory brainstem evoked potential patterns and later neurodevelopment demands further clarification. This study suggests the usefulness of auditory brainstem evoked potential assessment to provide information about electrophysiologic deviation of the auditory pathway in patients with early-treated congenital hypothyroidism.     

Auditory brainstem evoked potentials during sleep apnea

Auditory brainstem evoked potentials (ABEPs) were recorded from seven subjects with predominantly central sleep apnea. ABEPs were recorded during: (1) waking, (2) non-REM sleep between apneic episodes, (3) first half of apneas, and (4) second half of apneas. Latencies of vertex positive peaks III, V, and VI as well as the V-III interpeak latency difference were determined, and the effect of apnea phase on these measures were evaluated. The measures studied did not reveal chronic or acute functional abnormality of auditory brainstem, which may result from or cause apneic episodes during non-REM sleep. The normality and stability of ABEPs during apneic sleep indicate effective compensatory mechanisms in auditory brainstem. Brainstem functional changes associated with central apneas may not be reflected in the ABEP measures studied, unless they are part of a more extensive dysfunction.     

听觉诱发电位及体感诱发电位在颅脑外伤致昏迷患者的应用

严重颅脑损伤昏迷患者脑功能的监测是判断预后和指导治疗的重要手段。听觉诱发电位(BAEP)及体感诱发电位(SSEP)因其方便、无创并能连续实时监测昏迷患者相关神经传导通路电生理的变化,间接反映脑干上行激活系统、大脑皮层结构与功能的完整性,越来越成为临床对严重颅脑损伤昏迷患者预测预后和指导治疗的重要手段。本文就近年来相关研究进行综述,旨在指导临床实践。     

橄榄脑桥小脑萎缩脑干听觉诱发电位研究

本文对３５例橄榄脑桥小脑萎缩（ＯＰＣＡ）患者和３９例正常人进行脑干听觉诱发电位（ＢＡＥＰ）检查，结果发现ＯＰＣＡ病人ＢＡＥＰ异常１５例，阳性率４３％，主要异常是Ⅰ～Ⅲ峰间潜伏期延长和Ⅰ～Ⅴ波潜伏期双耳差值增大（Ｐ＜０．０５），提示ＯＰＣＡ主要电生理异常在听神经至桥脑下段之间，此外，还发现脑干电生理异常率与疾病严重程度和ＣＴ脑干萎缩程度有关。     

Important abnormalities in recordings of somatosensory evoked potentials in coma

We have chosen six illustrations showing how much vital information can be obtained from median nerve SEPs during the first 24 hours in coma. With avulsion of brachial plexus roots there was loss of SEPs at the cervical cord and the scalp from the affected side. In a severe injury of the cervical cord there was preservation of brachial plexus potentials, while SEPs at the cervical cord were absent. After critical deterioration in a case of repeated subarachnoidal hemorrhage, scalp SEPs with very short latency occurred, which is a finding suggestive of destruction of cortical SEP generators heralding a fatal outcome. In a case of brain injury combined with central hyperthermia, there was initially a loss of scalp SEPs probably due to the combined effect of these factors. In a case of brain injury there were bifid peaks at the scalp level. It is important to assess central sensory conduction time only to the first scalp SEP, otherwise an erroneously abnormal state may be inferred. In a patient with clinical and EEG evidence of brain death there was a loss of far-field thalamic potentials at the neck. It is important to be aware of such presentations to be able to provide corroborative assurance for the assessment of prognosis.     

Somatosensory and brainstem auditory evoked potentials in neurodegenerative system disorders

Brainstem auditory (BAEP) and somatosensory (SEP) evoked potentials to median and peroneal nerve stimulation were investigated in 25 patients with neurodegenerative system disorders: 9 Friedreich's ataxia, 7 hereditary motor sensory neuropathies, 3 familial spastic paraplegia, 3 olivopontocerebellar atrophy, 1 ataxia telangiectasia and 1 abetalipoproteinemia. BAEPs were abnormal in 39%, SEPs to both upper- and lower-limb stimulation were abnormal in 63%. Serial evoked potential testing paralleled the clinical progression. SEPs were more frequently and severely altered than BAEPs suggesting that SEP testing may be a more sensitive indicator of early involvement of afferent pathways in these disorders.     

Prognostic value of evoked responses and event-related brain potentials in coma

The behaviourally unresponsive patient, unable to exhibit the presence of cognition, constitutes a conundrum for health care specialists. Prognostic uncertainty impedes accurate management decisions and the application of ethical principles. An early, reliable prognosis is highly desirable. In this review investigations studying comatose patients with coma of different etiologies were selected. It is concluded that objective prognostication is enhanced by the use of electrophysiological tests. Persistent abnormalities of brainstem auditory evoked potentials and short-latency somatosensory evoked potentials reliably indicate the likelihood of irreversible neurological deficit or death. Meanwhile, the presence of "cognitive" event-related brain potentials (e.g., P300 and mismatch negativity) reflects the functional integrity of higher level information processing and, therefore, the likelihood of capacity for cognition. An approach that combines clinical and electrophysiological values provides optimal prediction of outcome and level of disability.     

Normal somatosensory evoked potentials in a child in persistent coma

Somatosensory evoked potentials have been useful in predicting coma outcome in children. We present a patient who failed to recover consciousness after a near-drowning episode and has remained in a vegetative state. The initial and subsequent somatosensory evoked potentials have been normal, illustrating that normal results do not necessarily portend a favorable outcome.     

Midbrain deafness with normal brainstem auditory evoked potentials

The authors report two cases of patients with word deafness. The word deafness occurred after a head injury for the first patient and after an arterio venous malformation embolization for the second patient. MRI demonstrated bilateral lesions of the inferior colliculi but brainstem auditory-evoked potentials (BAEP) were within normal limits. These cases demonstrated that lesions involving the two inferior colliculi induced pure word deafness but do not affect BAEP.     

脑干听觉诱发电位改变对Binswanger病的评估价值

目的用脑干听觉诱发电位方法检测Binswanger病的脑功能改变。方法对20例BD病患者、20例非痴呆脑血管病患者、20例老年健康人同时进行脑干听觉诱发电位（BAEP）检查。结果BAEP异常：BD病10例（50％），非痴呆脑血管病2例（10％），经统计学检查BD组BAEP与健康组、非痴呆脑血管病组有显著性差异，非痴呆脑血管病组与健康组无显著性差异。结论BAEP异常反应BD病患者有脑干功能受损和弥漫性脑功能障碍，并可作为BD病患者脑功能损害检查敏感指标，以及与非痴呆脑血管病患者鉴别诊断的一个辅助检查方法。     

Changes in auditory P300 event-related potentials and brainstem evoked potentials in diabetes mellitus

To investigate the influence of diabetes mellitus on higher cognitive functions electrophysiologically, we studied auditory P300 event-related potentials (P300) in 40 NIDDM patients, taking into account wave I-V latencies (I-V) in auditory brainstem evoked potentials, clinical parameters and head MRI findings. Compared with 20 controls, diabetics had significantly longer P300 and I-V latencies. P300 latencies in diabetics correlated with neither I-V. HbA₁, blood glucose levels, nor disease duration. Of the 13 diabetics investigated neuroradiologically, four had lacunar infarcts with prolonged electrophysiological values. The remaining nine had normal MRI scans, but their physiological parameters were still significantly longer than those of controls. These findings suggest that NIDDM can independently alter higher cognitive and the central auditory pathway functions. Our data also suggest that these alterations occur regardless of the recent metabolic derangement and disease duration. Cerebrovascular ischemia, if present, also appears to contribute in part to cognitive alterations.     

Ocular vestibular evoked myogenic potentials induced by air-conducted sound in patients with acute brainstem lesions

ObjectiveThe ocular vestibular-evoked myogenic potential (oVEMP), a recently documented otolith-ocular reflex, is considered to reflect the central projections of the primary otolithic afferent fibers to the oculomotor nuclei. The aim of our study is to define air-conducted sound oVEMP abnormality in patients with acute brainstem lesions and to determine the brainstem structures involved in the generation of oVEMPs.MethodsIn response to air-conducted tone burst sounds (ACS), oVEMP was measured in 52 patients with acute brainstem lesions. Individualized brainstem lesions were analyzed by means of MRI-based voxel-wise lesion-behavior mapping, and the probabilistic lesion maps were constructed.ResultsMore than half (n = 28, 53.8%) of the patients with acute brainstem lesions showed abnormal oVEMP in response to ACS. The majority of patients with abnormal oVEMPs had lesions in the dorsomedial brainstem that contains the medial longitudinal fasciculus (MLF), the crossed ventral tegmental tract (CVTT), and the oculomotor nuclei and nerves.ConclusionMLF, CVTT, and the oculomotor nuclei and nerves appear to be responsible for otolith-ocular responses in the brainstem.SignificanceComplemented to cervical VEMP for the uncrossed otolith-spinal function, oVEMP to ACS may be applied to evaluate the crossed otolith-ocular function in central vestibulopathies.