Vestibular function testing

PURPOSE OF REVIEW: This review provides an overview of vestibular function testing and highlights the new techniques that have emerged during the past 5 years. RECENT FINDINGS: Since the introduction of video-oculography as an alternative to electro-oculography for the assessment of vestibular-induced eye movements, the investigation of the utricle has become a part of vestibular function testing, using unilateral centrifugation. Vestibular evoked myogenic potentials have become an important test for assessing saccular function, although further standardization and methodological issues remain to be clarified. Galvanic stimulation of the labyrinth also is an evolving test that may become useful diagnostically. SUMMARY: A basic vestibular function testing battery that includes ocular motor tests, caloric testing, positional testing, and earth-vertical axis rotational testing focuses on the horizontal semicircular canal. Newer methods to investigate the otolith organs are being developed. These new tests, when combined with standard testing, will provide a more comprehensive assessment of the complex vestibular organ.     

Vestibular testing in basilar artery migraine

Vestibular function studies were performed in 20 children with symptoms suggesting basilar artery migraine. Sixteen children had abnormalities on bithermal caloric testing. Labyrinthine preponderance was found in 1 child with labyrinthine concussion and in 6 children with symptoms suggesting ischemia of the territory supplied by the basilar artery and the occipital branches of the posterior cerebral arteries. Directional preponderance was found in 4 children with symptoms suggesting ischemia of the posterior temporal branches of the posterior cerebral arteries. Five children had both labyrinthine and directional preponderance. Normal electronystagmographic findings were present in 4 children and correlated clinically with a milder illness. Head trauma was the triggering factor for the migraine in 5 children. Five children developed complex partial seizures and had evidence of directional preponderance (2 children) and combined labyrinthine and directional preponderance (2 children). The presence of abnormalities on electronystagmography in children with basilar artery migraine correlates with the severity of the disease. Directional preponderance or labyrinthine and directional preponderance are more frequently correlated with ischemia in the posterior temporal branches of the posterior cerebral arteries and may suggest a higher risk of developing vertiginous seizures when ischemia is prolonged.     

Patterns of arousal in comatose patients.

The EEG changes, with associated cardiorespiratory phenomena and, where possible, postmortem findings, are described in six patients in coma, with some reference to other similar cases. Spontaneously occurring periodic changes were observed at varying intervals between 20 s and 4 min but most commonly at 1/2-2 min. These involved simultaneous cardiorespiratory, EEG, and somatic motor phenomena related to changes in the level of arousal. It is suggested that a physiological periodicity of the arousal mechanisms exists which may be of importance in the understanding of the pathophysiology of comatose states.     

Vestibular testing by electrical stimulation in patients with unilateral vestibular deafferentation: galvanic evoked myogenic responses testing versus galvanic body sway testing.

OBJECTIVE: To investigate the agreement of a lesion site as indicated by two different vestibular tests with electrical stimulation, galvanic body sway testing (GBST) and galvanic evoked myogenic responses (galvanic vestibular evoked myogenic potential; galvanic VEMP) testing, in patients with unilateral vestibular deafferentation. METHODS: Nineteen patients with unilateral vestibular deafferentation were studied, and the criteria for patient selection were as follows: (1) absence of a caloric response to ice water on the affected side in a supine position, and (2) absence of VEMP to 95 dBnHL clicks on the affected side. We assessed the postural response of the subjects to long duration galvanic stimulation (1 mA, 5 s) by measuring the lateral displacement at the center of foot pressure with a cathode electrode on the forehead, and an anode electrode on the mastoid (GBST). We also recorded the electromyographic (EMG) activities of the sternocleidomastoid muscle (SCM) to short duration galvanic stimulation (3 mA, 1 ms) (galvanic VEMP) with a cathode electrode on the mastoid, and an anode electrode on the forehead. RESULTS: In 18 of the 19 patients, the lesion site indicated by GBST was identical to that indicated by galvanic VEMP. Fourteen patients had abnormal results in both tests while 4 patients had normal results in both tests. One patient with acoustic neuroma had normal results in GBST but abnormal results in galvanic VEMP. CONCLUSIONS: These results suggest that electrical stimulation in these two tests stimulates the same area of the peripheral vestibular afferent system, although the duration of stimulation was different, and that the estimate of the lesion site indicated by these tests in patients with complete or nearly complete unilateral vestibular damages is reliable. SIGNIFICANCE: These results suggest that short-duration galvanic stimulation as well as long-duration galvanic stimulation stimulates the vestibular system at the same level.     

长程脑电图监测对评估昏迷患者预后的应用价值

目的探讨长程脑电图监测和临床检测指标对评估昏迷患者预后的应用价值。方法对26例昏迷患者（男15例，女11例，年龄17～90岁）急性期进行长程脑电图监测、改良Glasgow昏迷评分以及半球复杂性的分析，随访患者至昏迷后2个月，并进行Glasgow预后评分，将长程脑电图监测和临床检测指标结果和昏迷患者预后进行相关分析；观察昏迷患者半球复杂性随时间的变化及其与预后的关系。结果长程脑电图监测对昏迷患者预后评估的特异度（77．8％）、准确度（92．3％）均较临床检测指标改良Glasgow昏迷评分高。脑电图分级与Glasgow预后评分进行线性相关分析，相关系数r=0．81，P〈0．01；改良Glasgow昏迷评分和Glasgow预后评分进行线性相关分析，相关系数r=-0．39，P〈0．01。患者病情变化时，脑电图改变出现在改良Glasgow昏迷评分改变之前。所观察的全部26例昏迷患者其左、右半球复杂性的熵值差异均无统计学意义，熵值随时间的变化呈6种图形，其中4种图形的昏迷患者Glasgow预后评分指标不良；2种图形的患者预后指标良好。结论对昏迷患者进行长程脑电图监测，在评价脑功能和预测昏迷患者的预后两方面有较好的应用价值。     

Prevalence of nonconvulsive status epilepticus in comatose patients

BACKGROUND: Nonconvulsive status epilepticus (NCSE) is a form of status epilepticus (SE) that is an often unrecognized cause of coma. OBJECTIVE: To evaluate the presence of NCSE in comatose patients with no clinical signs of seizure activity. METHODS: A total of 236 patients with coma and no overt clinical seizure activity were monitored with EEG as part of their coma evaluation. This study was conducted during our prospective evaluation of SE, where it has been validated that we identify over 95% of all SE cases at the Medical College of Virginia Hospitals. Only cases that were found to have no clinical signs of SE were included in this study. RESULTS: EEG demonstrated that 8% of these patients met the criteria for the diagnosis of NCSE. The study included an age range from 1 month to 87 years. CONCLUSION: This large-scale EEG evaluation of comatose patients without clinical signs of seizure activity found that NCSE is an underrecognized cause of coma, occurring in 8% of all comatose patients without signs of seizure activity. EEG should be included in the routine evaluation of comatose patients even if clinical seizure activity is not apparent.     

Continuous EEG monitoring in comatose intensive care patients

Introduction: It is unclear whether patients or subpopulations of patients might benefit from EEG monitoring. Methods: We conducted a prospective trial of continuous electroencephalogram monitoring (CEEG; 48 hours). Results: Eleven of 55 (20%) patients who underwent CEEG monitoring recorded seizures. Of patients with acute structural brain lesions (ASBLs), 10 of 31 (32%) patients experiences recorded seizures, whereas only 24 (4%) patients with metabolic encephalopathies experienced recorded seizures (p<0.01). Six patients with ASBLs (11%) and one patient with metabolic encephalopathy (4%) had spikes/interictal epileptiform discharges (p=0.087). Conclusion: Our study suggests that CEEG monitoring may be more valuable for detection of seizures in patients with ASBLs than in patients with metabolic encephalopathies.     

Sensorimotor central conduction time in comatose patients.

Motor evoked potentials (MEPs) following magnetic stimulation were recorded in 22 patients comatose as a result of head injury (13 cases), stroke (7 cases) or anoxia (2 cases). Somatosensory evoked potentials (SEPs) from median nerve were recorded as well in 19 cases in the same session. Thirteen patients died or remained vegetative (59.1%), 3 were severely disabled (13.6%) and 6 showed a good recovery (27.3%). MEPs were significantly related to the outcome; they appeared to be a more accurate prognostic indicator than the Glasgow Coma Scale (GCS). However, 1 out of 6 patients with bilaterally absent MEPs (16.7%) showed a good recovery. SEPs were significantly related to the outcome as well, but the combined use of SEP and MEP improved the outcome prediction, decreasing the rate of false negatives. Two patients had normal sensorimotor function, 13 a combined sensorimotor dysfunction, while 4 had a pure motor dysfunction. Our results suggest that SEPs and MEPs may improve the assessment of sensorimotor dysfunction in comatose patients. A significant relationship between MEPs and outcome appears to exist, but the assessment of MEP reliability requires further study.     

Central somatosensory conduction time in comatose patients.

Somatosensory conduction time between the dorsal column nuclei and the cerebral cortex may be measured following median nerve stimulation by recording evoked potentials from both scalp and neck. Central conduction times were significantly increased relative to normal (5.6 +/ 0.5 msec) in 11 of 24 comatose patients. Results within 10 and 35 days of onset of coma were correlated with the final clinical outcome. Conduction times were independent of serum phenobarbital (0 to 630 mumol per liter) and of central body temperature (35.0 to 38.5 degrees C). Serial studies in coma demonstrated (1) short-term increases during temporary metabolic disorders, and (2) sustained increases with gradual recovery over many months, particularly after head injury.     

昏迷患者非惊厥性癫痫持续状态的临床特点

目的 探讨昏迷患者非惊厥性癫痫持续状态(NCSE)的临床特点.方法 回顾性分析6例昏迷NCSE患者的临床资料.结果 6例患者中1例病毒性脑炎,1例大面积脑梗死,2例脑外伤,1例心肺复苏术后缺血缺氧性脑病,1例肾移植后代谢性脑病.其中,2例出现躁动,1例摇头、嘴唇咂动,2例四肢微小抽动,1例颜面抽动.所有患者的持续EEG(CEEG)监测均出现广泛或者局灶并发广泛的异常放电.结论 昏迷患者发生NCSE时多表现为躁动或面部、四肢微小抽动,CEEG监测能发现异常放电,有助于指导临床诊治.     

40 Hz--middle latency auditory evoked response in comatose patients

Brain-stem auditory evoked response (BAER) and 40 Hz middle latency auditory evoked response (40 Hz AER) were elicited in 12 comatose patients. The concept of a midbrain generator of 40 Hz AER is being discussed.     

昏迷患者的脑干听觉诱发电位与耳蜗电图联合研究

预测及判断昏迷患者的预后。方法对２０例昏迷患者进行脑干听觉诱发电位（ＢＡＥＰ）与耳蜗电图（ＥｃｏｃｈＧ）联合测试，同时用格拉斯哥昏迷量表（ＧＣＳ）评分。结果这种联合测试可使ＢＡＥＰ的Ⅰ波分辨率提高１２．５％。ＢＡＥＰ示脑干严重病损者，预后肯定不良，无假阳性；而ＢＡＥＰ正常者则因多种原因（如仅早期检测１次等）而有一定的假阴性。ＧＣＳ无假阴性，但因病因关系有一定假阳性。结论ＢＡＥＰ预测昏迷患者的预后时最好同时测试ＥｃｏｃｈＧ，有助于临床提高其判断的准确性     

Long-lasting EEG reactions in comatose patients after repetitive stimulation

Twenty patients with severe head injury and a Glasgow Coma Scale of 4-6 were subjects of a multimodality EP study. After EEG recording during rest (control 1) 60 mechanical vibration stimuli and 60 visual stimuli (interstimulus interval 10 sec) were applied. Thereafter a second EEG (control 2) was measured. To quantify a long-lasting stimulated EEG alteration, control 2 was compared with control 1 on the basis of the spectral theta/beta ratio calculated from central derivations. In 50% of the patients the theta/beta ratio was changed in control 2 and therefore a long lasting stimulation effect can be assumed. Stimulus-induced cardiac alterations were also found.     

Vestibular perception in patients with acquired ophthalmoplegia

Using a perceptual technique it is shown that patients with chronic external ophthalmoplegia have shortened vestibular responses. It is postulated that this is secondary to the retinal image slip experienced by these patients during head movements and a useful compensatory mechanism to suppress motion-induced sickness and spatial disorientation.     

Surgical management of comatose patients with cerebellar infarction

A series of 20 patients with cerebellar infarction were classified into four groups based on the clinical and CT findings. Two comatose patients who developed acute hydrocephalus (Group 2) are presented and were successfully treated with external ventricular drainage (EVD) alone. Continuous post-operative monitoring of intracranial pressure (ICP) demonstrated that EVD had sufficiently controlled ICP and therefore suboccipital decompression of the cerebellum was not indicated even though the patients were not immediately responsive to EVD. Both patients made a gradual recovery: a 57-year-old woman, independently ambulatory, was discharged to her home and a 76-year-old woman, ambulatory with assistance, was discharged to a rehabilitation hospital. The results of our two cases suggest that EVD should be the first treatment in cases of cerebellar infarction with cerebellar swelling or oedema accompanied by hydrocephalus. Posterior fossa decompression and removal of infarcted cerebellar tissue should be indicated only in cases where ICP can not be controlled by EVD, even if there is no immediate recovery of the patient's impaired consciousness. Reviewing the literature pertinent to our two cases, the use of ventricular drainage alone in the management of cerebellar infarction with ischaemic cerebellar swelling is discussed.