The orbicularis oculi reflex in multiple sclerosis

Abnormal control of orbicularis oculi reflex excitability in multiple sclerosis

Brain lesions in patients with multiple sclerosis may lead to abnormal excitability of brainstem reflex circuits because of impairment of descending control pathways. We hypothesized that such abnormality should show in the analysis of blink reflex responses in the form of asymmetries in response size. The study was done in 20 patients with relapsing-remitting multiple sclerosis and 12 matched healthy subjects. We identified first patients with latency abnormalities (AbLat). Then, we analyzed response size by calculating the R2c/R2 ratio to stimulation of either side and the mean area of the R2 responses obtained in the same side. Patients with significantly larger response size with respect to healthy subjects in at least one side were considered to have abnormal response excitability (AbEx). We also examined the blink reflex excitability recovery (BRER) and prepulse inhibition (BRIP) of either side in search for additional indices of asymmetry in response excitability. Neurophysiological data were correlated with MRI-determined brain lesion-load and volume. Eight patients were identified as AbLat (median Expanded Disability Status Scale–EDSS = 2.75) and 7 of them had ponto-medullary lesions. Nine patients were identified as AbEx (EDSS = 1.5) and only 2 of them, who also were AbLat, had ponto-medullary lesions. In AbEx patients, the abnormalities in response size were confined to one side, with a similar tendency in most variables (significantly asymmetric R1 amplitude, BRER index and BRIP percentage). AbEx patients had asymmetric distribution of hemispheral lesions, in contrast with the symmetric pattern observed in AbLat. The brainstem lesion load was significantly lower in AbEx than in AbLat patients (p = 0.04). Asymmetric abnormalities in blink reflex response excitability in patients with multiple sclerosis are associated with lesser disability and lower tissue loss than abnormalities in response latency. Testing response excitability could provide a reliable neurophysiological index of dysfunction in early stages of multiple sclerosis.

Blink Reflex Abnormalities in Chronic Alcoholics

PURPOSE

The aim of the present study was to evaluate the efficacy of blink reflex as a method for obtaining early diagnosis of cranial nerve involvement in alcoholic patients.

MATERIALS AND METHODS

The study was conducted on 30 male alcoholics with a mean age of 43 years. They had histories of alcohol abuse for at least 6 years (mean: 25). At the time of recording, they had undergone detoxification treatment for a mean of 27 days.

RESULTS

R1 (early response), R2Y (second ipsilateral response), and R2C (second contralateral response) latencies in alcoholics were prolonged relative to controls and the differences were statistically significant (p < 0.02, p < 0.001, p < 0.001, respectively). According to the defined criteria, 40% of the patients had abnormal responses, and the most common abnormality was the unilateral prolongation of R1 (13%).

CONCLUSION

Finding abnormal blink reflex responses in alcoholic patients has suggested that blink reflex testing is a useful method for the evaluation of subclinical cranial nerve involvement in alcoholic patients. Blink reflex testing may be useful in detecting early changes and in the follow-up of alcoholic disorder.

Positron emission tomography scanning in essential blepharospasm

PURPOSE

To localize in the brain using positron emission tomography neuroimaging with (18)fluorodeoxyglucose [PET ((18)FDG)] differences in glucose metabolism between patients with essential blepharospasm (EB) and controls.

DESIGN

Prospective case-control study.

METHODS

Positron emission tomography neuroimaging with (18)fluorodeoxyglucose was performed in 11 patients with EB and 11 controls matched for age and gender. Global analysis of images was used to localize differences in glucose metabolism between groups.

RESULTS

Multiple cortical and subcortical abnormalities were observed in EB patients in comparison with controls. Cortical areas with the largest and most significant clusters of increased glucose uptake were the inferior frontal gyri, right posterior cingulate gyrus, left middle occipital gyrus, fusiform gyrus of the right temporal lobe, and left anterior cingulate gyrus. Cortical areas with the largest and most significant clusters of decreased glucose uptake were the inferior frontal gyri, ventral to the area of increased glucose metabolism. Subcortical abnormalities, consisting of increased glucose uptake, involved the right caudate and consisting of decreased glucose uptake, involved the left inferior cerebellar hemisphere and thalamus.

CONCLUSIONS

Global analysis of positron emission tomography neuroimaging with (18)fluorodeoxyglucose neuroimaging in EB patients in comparison with controls demonstrates a pattern of abnormalities involving several cortical and subcortical areas that control blinking, including the inferior frontal lobe, caudate, thalamus, and cerebellum.

The roles of blink reflex and sympathetic skin response in multiple sclerosis diagnosis

The neurological history and examination are important in multiple sclerosis (MS) diagnosis, but early and accurate diagnosis of MS often requires judicious use of paraclinical information. Electrophysiologic techniques have an important role in demonstrating lesions that are clincally silent but magnetic resonance imaging (MRI) is accepted as the most sensitive paraclincal test for detecting asymptomatic dissemination in space for MS patients. In order to test the sensitivity of electrophysiologic techniques in diagnosing asymptomatic MS lesions, we performed blink reflex (BR) and sympathetic skin response (SSR) studies on 13 female (mean age 39 -/+ 9 years) and 8 male (mean age 35 -/+ 14 years) patients with a diagnosis of definite MS who do not have any clinical symptoms nor signs referable to brainstem or autonomic system dysfunction. Forty three percent of patients on SSR testing and 40% of patients on BR testing demonstrated abnormal results. In countries with unfavorable economic conditions, diagnosis, especially the follow-up evaluation of MS patients, poses a major dilemma. The role of diagnostic techniques in MS diagnosis when MRI is available is an economic problem. Diagnostic evaluation adds to the cost of health expenses. We usually choose to perform MRI only at the initial diagnosis of MS and perform follow-up evaluations during remissions and exacerbations with the aid of electrophysiologic techniques. We stress the importance of electrophysiologic screenings in MS patients because they provide data that cannot be obtained through clinical evaluations only with a little cost.

Topodiagnostic value of blink reflex R1 changes: a digital postprocessing MRI correlation study

The aim of the study was to investigate the relation of the blink reflex R1 arc to known anatomical brainstem structures. Acute vascular brainstem lesions as identified by magnetic resonance imaging (MRI) of patients with isolated R1 pathology were superimposed into a stereotactic anatomical atlas using a new method of digital postprocessing. Isolated acute brainstem lesions were documented by diffusion-weighted MRI in 12 of 24 patients with unilateral R1 pathology. The lesions were located in the ipsilateral mid- to lower pons. In three patients only, the lesion had partial contact with the principal sensory nucleus of the trigeminal nerve (PSN) on at least one level. In two patients, the lesion involved the medial longitudinal fasciculus. Most lesions were located medially and ventrally to the PSN on transverse slices. Our results underline the high localizing value of changes in the R1 component of the blink reflex in patients with ipsilateral pontine functional deficits. Although available physiological evidence suggests that the R1 component of the blink reflex traverses an oligosynaptic pathway, this MRI study does not support the view that synaptic transmission in the PSN subserves R1. The reflex arc probably descends more medially and ventrally on its course to the facial nucleus.

Blink reflex abnormalities in diabetes mellitus

BACKGROUND

Damage of the peripheral nervous system is particularly frequent in diabetes mellitus (DM), but somatic cranial neuropathies usually presenting as mononeuropathies are rare. Oculomotor and facial nerves are among the most commonly affected, whereas the Vth, IXth and Xth cranial nerves are less often affected. While existing neurophysiological tests in the subclinical diagnosis of damage to the peripheral nerve in diabetic patients have advanced, the same does not hold true for the subclinical diagnosis of the central nervous system (CNS). Electrophysiological studies such as the blink reflex was shown to be an effective method for revealing subclinical involvement of cranial nerves in generalised neuropathies. The aim of the present study was to evaluate the efficacy of blink reflex as a method for obtaining early diagnosis of cranial nerve involvement in diabetic patients frequently affected with peripheral neuropathy.

METHODS

Twenty diabetic patients with electrophysiologically confirmed neuropathy were included in the present study for the evaluation of blink reflex. Patients with earlier cranial nerve involvement were excluded.

RESULTS

Abnormal blink reflex responses were found in 55% of patients studied. R2Y and R2C latencies in diabetic patients were prolonged relative to controls (p<0.001 and p<0.001, respectively). However R1 values in diabetic patients did not differ significantly from those of normal controls (p<0.5). R2Y and R2C prolongation showed a positive correlation with the duration of disease (p=0.015 and p=0.009, respectively). However the same correlation could not be found with R1 values. No correlations were found between R1, R2Y, R2C values and HbA(1c) nor between R1, R2Y, R2C values and patients' age.

CONCLUSION

We suggest that blink reflex testing is a useful method for obtaining early diagnosis of cranial nerve compromise in diabetic patients who do not show any clinical symptoms or signs of CNS involvement.

Wavelet decomposition of the blink reflex R2 component enables improved discrimination of multiple sclerosis

OBJECTIVES

The blink reflex R2 component was subjected to wavelet decomposition for time feature extraction in order to classify the functional status of patients with multiple sclerosis.

METHODS

The blink reflex was recorded bilaterally with unilateral stimulation of the supra-orbital nerve in 37 normal subjects and 9 patients with multiple sclerosis (MS). The late component, R2, was subjected to time-frequency decomposition using the Daubechies-4 wavelet. Using the time-frequency coefficients, the mean time of the R2 wave as well as the standard deviation of the R2 interval were calculated in each trial. The wavelet transform enables noise reduction by allowing selective use of frequency bands with high signal-to-noise ratio for time feature extraction; therefore automatic estimation of time parameters is robust. The distribution densities of the mean and the standard deviation of the R2 wave duration for the set of trials for each subject were computed.

RESULTS

An appreciable difference in the densities of the two parameters extracted in the wavelet domain was seen between normals and patients. This is in contrast to the onset latency of R2 which poorly discriminates MS patients from normals.

CONCLUSION

The results suggest that the mean and standard deviation of the R2-time robustly estimated using wavelet decomposition can be used to support clinical diagnosis in tracking the functional status of patients with diseases like multiple sclerosis.

Analysis of the corneal reflex with air puff: normal controls and patient groups

Though there are several reports published about the corneal reflex elicited by different methods, a standardized electrophysiologic study with air puff in man has not been published. The aim of this study is to standardize the corneal reflex elicited by air puff to cornea. The authors studied the corneal reflex with air puff and direct touch by using a standardized method in patients with thalamic hemorrhage (n = 15), hemispheric infarction (n = 9), brainstem infarction (n = 9), multiple sclerosis (n = 12), and Bell's palsy (n = 12) and in normal control subjects (n = 21). The conventional blink reflex (BR) was also studied. The reflex responses were recorded from both orbicularis oculi muscles by air puff and direct touch to cornea in addition to the electrical stimulation of the supraorbital nerve. No statistical difference could be detected between the responses elicited by air puff or direct touch to cornea (P > 0.05). Corneal reflex responses were statistically different from the R2 response of the BR (P < 0.005). Because the responses elicited by direct touch and air puff to cornea are identical, air puff to cornea can be used confidently to study the corneal reflex.

A neurophysiological approach to brainstem reflexes. Blink reflex

The blink reflex (BR) is a generalised phenomenon in mammals. Its teleological protective eye function is perhaps the reason why the BR can be provoked by a multitude of stimuli. As corneal and glabellar reflexes, BR has an inveterate use in the neurological exploration. Some of its physiopathological aspects were discussed more than 100 years ago, and soon half a century will have passed since the first electrophysiological study was published. This review focuses on the BR elicited by the electrical stimulation of the trigeminal supraorbital nerve, a controlled and reliable model in clinical neurophysiology. The electrically elicited BR is an exteroceptive-nociceptive reflex recorded on the orbicularis oculi muscle and formed by three components: the two principal ones, R1 and R2, of well-known characteristics, and a third, R3, of increasing interest, to which there is wide mention. The trigeminal afferent limb reaches the facial efferent one by means of a long and quite complex central pathway located at the brainstem bulbopontine level. The anatomical substrate and criteria of the rich topographical lesional semiology of the BR are established. The importance of the suprasegmental influences upon the reflex, coming mainly from the cerebral cortex and basal ganglia, as well as the impairment caused by their damage, will be emphasised. Special attention is paid to the relationship between the reflex and the dopaminergic system, and the consequences of its derangement. The methods of habituation and suppression-recovery of the BR are extensively and critically reviewed. These methods measure its excitability and serve in practice for the pathophysiological study of numerous diseases. The relationship of the BR with the spontaneous blinking is considered, and the existence of a primary inhibitory reflex on levator palpebrae muscles, previous to the active reflex response of the orbicularis, is proposed. The electrophysiological characteristics of the glabellar reflex, the corneal reflex, the acoustic, photic and somatosensory provoked BR, the ontogeny, and some of the common factors influencing the reflex, such as sleep, are also discussed. The strategic position of the neural structures of the BR, in an area involved in the gating of the various sensory-motor systems and the relative ease to its evaluation with common methodology used in clinical neurophysiology, makes the BR an essential tool for the diagnosis and pathophysiological insight into an important number of human neurological disorders.

Brain-stem trigeminal and auditory evoked potentials in multiple sclerosis: physiological insights

Thirty-six patients with multiple sclerosis were evaluated by means of brain-stem trigeminal and auditory evoked potentials. The brain-stem auditory evoked potentials (BAEPs) were abnormal in 26 patients (72.2%). Brain-stem trigeminal evoked potentials (BTEPs) yielded similar results, showing distorted waveforms and/or prolonged latencies in 25 patients (69.4%). As expected, the MRI proved to be the most efficient single test, revealing plaques in 86.4% of the patients evaluated. However, the diagnostic accuracy of MRI was lower than that provided by the combination of the BTEP and BAEP (88.9%). Moreover, in patients having signs of brain-stem involvement, the BTEP, alone and in combination with the BAEP, proved to be more sensitive than the MRI in revealing brain-stem lesions. Correlation between clinical and BTEP findings could be found only in those patients who presented with signs of trigeminal involvement such as trigeminal neuralgia or dysesthesiae. The analysis of the BTEP waveforms showed two distinct types of abnormality-a peripheral type and a central type-suggesting plaques in distinct locations. Both the BTEP and the BAEP demonstrated a correlation with the clinical course of the disease and the condition of the patient at the time of the evaluation. Relapse of the disease was associated with a marked prolongation of the central conduction time in the BTEP and in the BAEP, suggesting the application of such studies to the monitoring of unstable patients in the evaluation of new therapeutic protocols.

Contralateral early blink reflex in patients with HTLV-I associated myelopathy/tropical spastic paraparesis

Thirty-two Japanese patients with HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP) were studied by means of the electrically elicited blink reflex and three responses (R1, R2, R3) were registered. 69% of the patients displayed a uni- or bilateral crossed R1 response (R1k) as compared to 11% in the control group. A positive correlation between R1k and an exaggerated jaw jerk reflex was found in the patients. Central abnormalities of the nervous system with diminished presynaptic inhibition acting in the interneuronal input of the brainstem of HAM/TSP patients was the most likely cause. It could lead to the unmasking of crossed trigemino-facial pathway reflex which is present in the normal population from birth. These results strongly support the supraspinal involvement of the central nervous system (CNS) in HAM/TSP more than usually thought.

Blink reflex in patients with an ischaemic lesion of the brain-stem verified by MRI

The electrically elicited blink reflex was investigated in 25 patients with ischaemic lesions of the pons or the medulla oblongata. Only patients with a lesion on MRI appropriate to the clinical syndrome were included. Twenty patients had an infarction of the pons, bilateral in 5. Additional 5 patients had an infarction of the dorsolateral medulla oblongata. Patients with hemispheric lesions were excluded. Four of the 5 patients with Wallenberg's syndrome showed delayed R2 components to stimulation ipsilateral to the lesion. Additional loss of the ipsilateral R1 component was observed in 1 patient. Fifteen of the 20 patients with pontine infarctions had pathological blink reflexes. All 6 patients with a unilateral pons lesion and an abnormality of R1 had this abnormality on the side contralateral to the lesion. In 3 cases with bilateral pontine infarction R1 was abnormal on one side or on either side. Of 11 patients with a normal R1, 6 had isolated abnormalities of R2 without consistent correlation to the side of the lesion. We conclude that abnormalities of the blink reflex are of minor localizing value in pontine infarction. This may be explained by the fact that a pontine infarction affects either the reflex arch itself or descending pathways that have a modulating influence on the reflex arch. Infarctions of the medulla oblongata, however, have characteristic abnormalities that have already been described.

Blink reflexes and magnetic resonance imaging in focal unilateral central trigeminal pathway demyelination

The electrically elicited blink reflex allows quantitative analysis of the corneal reflex which traverses the trigeminal and facial nerves and the brainstem. Two patients presenting with symptomatic unilateral trigeminal lesions are described, in whom the blink reflexes showed conduction block and slowing at predictable sites in the central pathways, and magnetic resonance imaging confirmed precisely the clinical and electrophysiological localisation.

Effects of general anesthesia on the human blink reflex

The blink reflex was studied in 10 patients undergoing elective procedures under general anesthesia. Anesthetic agents were isoflurane, halothane, nitrous oxide, methohexital, and thiopental in various combinations. At induction, blink reflexes were diminished by low-dose thiopental (1-1.5 mg/kg) and abolished by high-dose thiopental (4-8 mg/kg) and methohexital (1.5 mg/kg). Blink reflexes were absent during halogenated volitile inhalational anesthesia and did not return until patients were in the recovery room, well after end-tidal anesthetic levels were zero by mass spectroscopy. Recovery of consciousness and the ability to blink on command often preceded return of any blink reflex activity, indicating that the blink reflex is not useful as a postoperative test of facial nerve function in the operating room after anesthesia. In six patients, blink reflexes were still diminished 2-3 hours after cessation of anesthesia, at a time when patients were fully oriented and corneal and eyelid reflexes were clinically normal. This finding suggests that the blink reflex might be a sensitive test of subtle CNS dysfunction after inhalational anesthesia and potentially could serve as a useful objective indicator of recovery from anesthesia for outpatient surgery.

Influences of dopaminergic systems on the blink reflex

The effect of the anti-dopaminergic drug haloperidol (6 mg/day i.m. for 2 days) on the blink reflex elicited by electric stimulation of supraorbital nerves was investigated in 12 adult volunteers. A significant increase in amplitude of the early component (R1) of the reflex was observed. This increase disappeared within 5 days of stopping the drug. Possible neural systems which might be involved in these effects are considered.

Electrically elicited blink reflex and early acoustic evoked potentials in circumscribed and diffuse brain stem lesions

In the present paper, the function of the brain stem in patients with brain stem lesions of various aetiology is investigated with electrophysiological methods. The clinical observations are supplemented by experimental investigations on cats, in which the blink reflex and the early acoustic evoked potentials were registered during the acute elevation of intracranial pressure. The findings in patients with circumscribed space-occupying lesions in the posterior fossa document that the registration of the BR and the BAEP have a functional diagnostic significance above and beyond the neurological and radiological investigation. In the case of the cerebellar space occupations, specific alterations could not be observed. On the contrary, the alterations of BR and BAEP indicate a general disturbance of brain stem function, possibly as a result of a general increase of intracranial pressure. In cerebellopontine angle tumours, both BR and BAEP showed specific alterations which were usually asymmetrical. The BR changes ipsilateral to the tumour are of major topodiagnostic significance, whereas the alterations of the contralateral potential are especially informative in the registration of BAEP. The alterations of BR and BAEP also allow an appraisal of the localization and extent of the lesion in primary space occupations in the brain stem: A pathological R1 indicates a pontine lesion, whereas pathological R2 responses are found in medullary and in oral pontine and mesencephalic lesions. In contrast to cerebellopontine angle tumours, the BAEP tends to show symmetrical alterations in primary brain stem lesions. The prolongations of interpeak latencies correspond to the brain stem segment concerned, and the same also applies to pathological amplitude reduction and deformations of individual potentials. In patients with localized brain stem damage, the reflex pathway of R2 is discussed on the basis of the BR findings. In contrast to the view held up to now that only structures situated caudal of the facial nucleus area are responsible for the genesis of the R2 response, it is assumed on the basis of our own observations that pontomesencephalic structures rostral to the facial nuclei are also important for the genesis of R2. Registration of BR and BAEP in patients with acute diffuse brain stem damage shows that both methods have a high diagnostic and prognostic value. Isolated damage and combined brain stem lesion can be demonstrated and the course can be followed up. Normalization of pathological findings reflects clinical recovery, and conversely a secondary deterioration indicates the presence of complications.(ABSTRACT TRUNCATED AT 400 WORDS)

The diagnosis of multiple sclerosis. Contribution of non-clinical tests

A group of 89 patients in whom multiple sclerosis (MS) has been clinically diagnosed with varying degrees of certainty, and 25 patients with optic neuritis (ON), were subjected to the following electrophysiological tests: visual evoked response (VER), auditory brainstem-evoked response (ABER), somatosensory-evoked response (SSER), blink reflex and electronystagmography (ENG). All these patients also underwent computerized tomography (CT scan) and analysis of cerebrospinal fluid (CSF). A new diagnostic procedure is proposed, combining optimum detection of definite MS with optimally economical use of the above-mentioned non-clinical tests. The results for the MS patients show that definite MS can be diagnosed much more frequently (72%) if abnormal results in the above-mentioned tests are accepted as evidence of a (subclinical) CNS lesion. Application of the clinical diagnostic criteria of McAlpine yielded "definite MS" only in 27% of our patient material. Our diagnostic criteria showed evidence for MS in 36% of the patients clinically diagnosed as having ON. The test results were inconclusive as regards the possibility of the remaining ON patients developing MS in the future.

Jaw, blink and corneal reflex latencies in multiple sclerosis

Jaw, blink and corneal reflexes, which all involve the trigeminal system, were recorded in 54 patients with multiple sclerosis; thirty-seven of these patients were classified as having definite multiple sclerosis and 17 as indefinite multiple sclerosis, according to Schumacher's criteria. The jaw reflex was abnormal less frequently than either of the other two reflexes, but in four cases it was the only abnormal reflex found. Testing a combination of two or three trigeminal reflexes did not yield a higher incidence of abnormalities than testing the blink or corneal reflex alone. Nine patients showed abnormal reflexes which were unexpected on the basis of clinical symptoms. The combined recordings demonstrate at least one abnormal reflex in 74% of the patients. The various types of reflex abnormalities reflect major damage to different parts of the trigeminal system and may therefore make an important contribution to the diagnosis of multiple sclerosis.

Electrophysiological disorders in multiple sclerosis and optic neuritis

Visual evoked response (VER), auditory brainstem evoked response (ABER), somatosensory evoked response (SSER), blink reflex and electronystagmographic (ENG) investigative methods were applied to a group of 89 patients with Multiple Sclerosis (MS) and Optic Neuritis (ON). The MS patients were classified as definite (n = 31), probable (n = 31) and possible (n = 27). The aim of this study was to determine the diagnostic value of the five electrophysiological tests in MS. VER and ABER recordings were found to reveal the highest number of asymptomatic abnormalities (33 and 31 percent respectively). The combination of VER, ABER and ENG revealed all possible electrophysiological disorders. As these tests are completely non-invasive it is proposed, that a combination of two of these three tests is useful for the detection of a second silent lesion in patients with suspected MS showing purely spinal signs (VER, ENG, ABER) and/or a history of uncomplicated ON (ABER, ENG).

Brain stem auditory evoked potentials and blink reflexes in multiple sclerosis

Brain stem auditory evoked potentials (BAEP) and the blink reflex (BR) were recorded from 50 patients with a wide spectrum of multiple sclerosis, to determine whether the combination of the two tests of brain stem function would yield a higher rate of abnormality than each test performed alone. Sixty-four per cent of patients had a BAEP abnormality and fifty-two per cent had an abnormal BR, but when the results were combined, seventy-six per cent were abnormal. The blink reflex was abnormal in all patients with symptoms suggestive of trigemino-facial pathology.

Changes in the recruitment pattern of single motor units in the blink reflex of patients with parkinsonism and hemiplegia

The recruitment pattern of single motor units (SMUs) was studied in the early (R1) and late (R2) blink reflex components in normal subjects (15), patients with parkinsonism (10) and with hemiplegia due to hemispheral lesions (5). Reflexes were evoked by constant current stimuli applied to the supraorbital nerve. SMU discharges were recorded in the preseptal part of the lower eyelid using a bipolar needle electrode. Thresholds of R1 and R2, latencies at the thresholds and the number of discharges in R2 were determined. In parkinsonism, the recruitment of SMUs in R1 was impaired, suggesting that the malfunction of the basal ganglia in this disorder is associated with a reduced excitability of neurons in the pontine brain-stem. In hemiplegia, the recruitment in both R1 and R2 could be impaired. The orderly function of neurones in the pontine and medullary pathways of these components appears to require facilitatory hemispheral influences. Signs of disinhibition occasionally found in R1 may point to an imbalance between facilitatory and inhibitory hemispheral influences upon the pontine pathway.

Evoked potentials and brain stem reflexes

The recording of evoked potentials (EPs) has become one of the most useful functional diagnostic techniques in the neurosciences during recent years. In combination with the neurophysiological investigation of brain stem reflexes (BSRs) EPs provide good information concerning circumscribed and diffuse brain and brain stem lesions. In this article the role of EPs and BSRs will be pointed out with special regard to their use in neurosurgery concerning awake and comatose patients as well. Pathological findings caused by extracerebral factors or due to neurological (systemic) and otological diseases will be discussed from the aspect of differential diagnosis only. Evoked potentials described in this paper are short latency potentials which are related to more or less defined generators in the peripheral and central nervous system. EPs of long latency seem to play a role in cognitive, affective and integrative functions of the central nervous system and they will not be dealt with in this article. In recent years an increasing number of review articles and monographs dealing with several aspects of evoked potentials has appeared [16, 17, 18, 25, 69, 80, 84, 122, 123, 124, 127, 130].

Brainstem involvement in multiple sclerosis: a clinical and electrophysiological study

A major aim of this study was to determine the diagnostic value of 4 electrophysiological tests in MS, and particularly their effectiveness in detecting signs of brainstem involvement. Therefore, auditory brainstem evoked response (ABER), somatosensory evoked response (SSER), blink reflex and electronystagmographic (ENG) investigative methods were applied to a group of 89 patients with definite, probable or possible multiple sclerosis (MS). The 4 methods yielded interdependent data, especially where the brainstem function was concerned, thus it can be concluded that a single demyelinating lesion may cause a combination of electrophysiological disorders within a small structure such as the brainstem. ENG recordings were found to reveal the highest number of asymptomatic abnormalities. The combination of ABER and ENG tests revealed electrophysiological disorders in 81% of all patients. The blink reflex and the SSER tests gave hardly supplementary information.

Unilateral reduction of the early and late blink reflex component in hemiparkinson syndrome

Electrically evoked blink reflexes were recorded in 10 patients with unilateral tremor and/or rigor, mostly diagnosed as hemiparkinson syndrome. Five of the patients could be investigated before and after stereotaxic thalamo-subthalamotomy. The EMG activity of the early and late components was quantified by means of averaging and integrations techniques. In addition, the latencies of the reflex components were determined. The major finding was a unilateral decrease of the EMG activity of both the early and late components confined to the clinically affected side. This pattern points to a lowered state of excitability of neurons in or close to the facial nucleus, probably due to a dysfunction of contralateral EPMS structures. A loss of facilitatory influences from EPMS centers, e.g. the nigro-striatal system, on brain stem neurons in the area of the facial nucleus appears most probable. The latencies of the early and late components were mostly normal. After stereotaxic surgery, the BR activity was decreased bilaterally. The difference between the affected and unaffected sides, however, was nearly unchanged. At present an unspecific postoperative effect cannot be excluded.

Some observations on the blink reflex in posttraumatic coma

Blink reflex studies were carried out on 51 comatose patients with signs of brain stem impairment due to head injury. Twenty-five patients were studied in acute coma on day 1 or 2 after trauma. Twenty-six patients were studied in prolonged coma during days 3-12 after brain injury. Brain stem involvement was divided clinically and by CT scan into secondary lesions due to supratentorial mass displacement and primary lesions due to direct violence to the brain stem. Further, the comatose states were separated by behavioural and EEG signs of sleep into "sleep' and more "alert' states. The blink reflexes were recorded after mechanical and electrical stimulation. Mechanical stimulation appeared to be more effective in evoking late responses than the electrical stimulus. The elicitability of the late responses was also dependent on the time of stimulation. During "sleep', usually accompanied by a spindle-EEG, the late responses were totally absent after both mechanical and electrical stimulation in acute coma. In more "alert' states, usually accompanied by high voltage delta waves in the EEG, the late responses, especially direct R2, could be frequently elicited by mechanical stimulation. These differences decreased during prolonged coma. All patients with signs of secondary brain stem involvement who had at least one late component in the acute stage of coma recovered well. So did all patients, with one exception, with primary brain stem injuries. Early recovery of the blink reflexes in cases of primary brain stem injury was a further favourable sign. Consistent absence of R2 (and R1) in prolonged coma indicated a bad outcome. The presence of all components in prolonged coma was of less prognostic significance than in the acute stage.

Quantitative analysis of blink reflexes in patients with hemiplegic disorders

Electrically evoked blink reflexes were investigated in 18 patients with hemiplegia and in 15 control subjects, using common electromyographic techniques. The EMG activities of the early and late components were quantitatively and integration. In addition, the latencies of the single components were determined. Regarding the EMG activity of the late components two major types of BR alteration could be distinguished. In type I stimulation of the clinically affected side evoked significantly decreased late components on both the affected and the unaffected sides. This pattern points to a lowered excitability of the brain stem trigeminal systems and may be associated with predominantly sensory disorders. In type II the decrease of the late components was confined to the affected side independent of the side of stimulation. This pattern may indicate a lowered excitability of the brain stem facial systems and/or of the lateral bulbar reticular formation and may be correlated with predominantly motor deficits. Both types are presumably due to a loss of facilitatory influences associated with the hemispheral lesion. Although the early component was frequently decreased on the affected side there was no consistent pattern and no relation to the alterations of the late components. The latencies of both responses, predominantly of the late ones were frequently prolonged, in particular following stimulation of the affected side. Comparison of the seemingly normal components in the patients with the corresponding control values pointed to a generally lowered blink reflex excitability in hemiplegic patients.

The value of brain stem auditory, visual and somatosensory evoked potentials and blink reflexes in the diagnosis of multiple sclerosis

Cervical and cortical somatosensory evoked potentials (SEP) following electrical stimulation of the median nerve and blink reflexes (BR) following electrical stimulation of the supraorbital nerve were recorded in 30 normal subjects aged 20-49 years. Subjects aged 40-49 had longer SEP latencies than subjects aged 20-39 years. A total of 29 slightly affected patients with multiple sclerosis (MS) aged 26-49 years, including four patients without clinical signs (suspected MS) and 19 patients with signs indicating only one lesion (possible MS) were examined by low-rate random-stimulated brain stem auditory (BAEP), checkerboard pattern-reversal visual evoked potentials (VEP), SEP and BR. Abnormal recordings by at least one of the examinations were found in all but three patients, and by all four tests in five patients. In patients with definite or probably MS, demonstration of clinically recognized or subclinical lesions was of minor diagnostic value, in contrast to the importance such findings had in patients with suspected or possible MS. Silent lesions were shown by at least one of the tests in the four suspected and in 13 of the possible MS patients, so these 17 patients could be transferred to a more certain diagnostic category. This reclassification was most often due to the BAEP recording. In patients with spinal signs, the combination of BAEP and VEP recording was sufficiently efficient. In patients with optic neuritis a combination of BAEP and SEP was preferred. No abnormal recordings were found in 15 normal subjects examined by all four tests.

Evaluation of various brain structures in multiple sclerosis with multimodality evoked potentials, blink reflex and nystagmography

Pattern reversal visual evoked potentials (VEP), blink reflexes, auditory brainstem evoked potentials (ABEP), spinal and scalp recorded somatosensory evoked potentials (SSEP), and nystagmographic records were investigated in 55 patients with multiple sclerosis (MS), who were separated in different categories of probability according to the clinical history, symptoms, and signs. The combined use of different electrophysiological methods forms a sensitive battery for investigating clinically uncertain cases of MS. It was stressed that care should be taken in the interpretation of the electrophysiological findings, since a single lesion in the central nervous system, particularly in the brainstem, may affect different functional systems simultaneously and therefore mimic a disseminated disease.

Chronic progressive myelopathy: investigation with CSF electrophoresis, evoked potentials, and CT scan

Chronic progressive myelopathy (CPM) is a difficult clinical problem. Many patients who present with CPM turn out to have a spinal form of multiple sclerosis (MS), but until there is clear lesion dissemination, a definite clinical diagnosis cannot be made. We have looked for MS-related abnormalities in 72 patients with CPM. The mean age of onset was 42 years, mean duration was ten years, and mean Kurtzke disability rating was 4.5. Studies performed were cerebrospinal fluid electrophoresis for oligoclonal banding, pattern-reversal visual evoked responses, blink reflex latencies, and computerized axial tomography. Oligoclonal banding was found in 32 patients (44%), patterned visual evoked responses were abnormal in 32 (44%), and blink latencies were abnormal in 40 (56%). A least one of these studies was abnormal in 61 patients (85%) and at least two in 48 (66%). The CT scan was abnormal in 38 )53%), 36 with atrophy and 3 with low-density or enhancing lesions. These results suggest that at least 44% of patients with CPM may have MS that could be diagnosed by oligoclonal bands. Other physiological tests suggesting diffuse or disseminated disease bring the total to 85%. Only autopsy follow-up will tell us the exact diagnostic accuracy of these studies in this complex syndrome.

Brain stem auditory evoked potentials and blink reflexes in quiescent multiple sclerosis

Brain stem auditory evoked potentials (BAEP) and blink reflexes (BR) were studied in 25 patients with multiple sclerosis (MS), the diagnosis being definite according to McAlpine's criteria, in the quiescent phase, without signs of brain stem involvement. BAEP abnormalities were found in 64% of the cases and BR abnormalities in 60%. A good correlation between the two tests was found in most patients. The abnormalities consisted of delayed latencies and/or high intraindividual variability in shape and latency of BAEP and BR components. It seems that demyelination of brain stem pathways results not only in conduction slowing but also in more serious dysfunction of the generators of the evoked components.

Cyclic alterations of blink reflexes: an EEG and EMG study during wakefulness and sleep

Studies of the blink reflex were undertaken in twelve normal subjects during wakefulness and different sleep stages. The early R1 and the late R2 components of the reflex were analyzed. R1 was present in only one subject during stage I sleep and subsequently disappeared in stage II to IV. In all subjects, R2 was gradually diminished and totally disappeared during stage IV. During the REM stage, R1 was seen in only four-out-of-twelve subjects but all R2 returned. Alterations of R1 and R2 of the blink reflex during different sleep stages suggest that the underlying mechanism includes both supranuclear and infranuclear activities. Our finding strengthens further the notion of dual hyponogenic mechanisms for sleep.

Blink reflex in hemiplegia

An electrophysiological study of the blink reflex was undertaken in 20 normal subjects and in 28 patients complaining of central facial palsy caused by unilateral hemispheral damage. In normal subjects, the latency, amplitude and organization of R1 and R2 responses are well known. Habituation of R2 responses occurred between 1 and 2 c/sec stimulation rate. R1 responses habituated at a higher stimulation rate (5 c/sec). In patients with unilateral hemispheral lesion, our results showed that changes in the blink reflex responses were bilateral. On the hemiplegic side the responses showed a decreased amplitude, while they were facilitated on the "normal" side. However, there was no change in latency of the two components of the reflex, on both sides. On the other hand, habituation of the late component occurred on the hemiplegic side for low stimulation rates: (0.5--1 c/sec), while on the "normal" side there was less habituation (3--4 c/sec), as compared with normal subjects. These results agree with those of experimental studies on cortical modulatory influences on brain-stem nuclei. They suggest a tactile origin of the two components of the blink reflex.

[Orbicularis oculi reflex after facial paralysis: decreased amplitude of reflex response and spreading to all hemifacial muscles after reinnervation (author's transl)]

After the acute stage of peripheral facial paralysis with nerve degeneration we find some signs of paresis after reinnervation due to insufficient motor recovery and associated movements due to faulty reinnervation. Electromyographical investigation of the orbicularis oculi reflex can be used for the objective evaluation of these two phenomena. This shows the following typical signs: 1. The amplitudes of the early and late reflex response are decreased on the affected side proportionate to the degree of paresis. 2. The response occurs in all reinnervated hemifacial muscles as a result of misdirection of fibres which originally innervated the orbicularis oculi muscle.

The blink reflex in coma and after recovery from coma

Comparative studies of the blink reflex in a series of head injuries through the stages of coma and recovery from coma in a series of miscellaneous hemispheral lesions, and in a normal series, reveals that, although the principal centre for the R1 component of the blink reflex seems to be localised in the upper pons, the seat of the R2 late component is in the reticular system. The reappearance of this late component of the blink reflex in our cases of coma although seeming to depend on the integrity of the mesencephalic formation, correlates with the recovery of the patient's alertness. On the other hand, habituation of this reflex depends on the integrity of global cognitive function, rather than on any localised centre. The roles of the cortex, selective attention, and emotional factors, are discussed. The recovery of the normal habituation of the blink reflex obtained by glabellar tapping was found to be a useful sign in the follow up of patients recovering from concussion and other lesions, such as subdural haematomas and brain tumours, with global mental impairment.

Blink reflex in Huntingon's chorea and Parkinson's disease

The electrically-evoked late response (R2) of the blink reflex has been determined in 8 well-documented cases of Huntington's chorea and in 19 Parkinsonian patients. The results obtained from the two groups are compared with those from 10 normal subjects. A statistically significant difference of some components of the blink reflex was obtained when the three groups were compared. In both pathological conditions, the habituation index, latency and differential latency can be considered to represent the opposite extremes from the same scale, providing further evidence of the neurophysiological antagonism between the two disease states. The blink reflex pattern in Huntington's chorea probably reflects a diminished brain-stem interneurone basal activity through an over-inhibition of dopaminergic receptors in the striatum. The electrophysiological analysis of the blink reflex in incipient Huntington's chorea can provide an objective diagnostic assessment. It might be an effective method of detection for dopaminergic-activated carriers asking for genetic counseling.

Alteration of orbicularis oculi reflex by posterior fossa tumors

✓ The orbicularis oculi reflex response to electrical stimulation of the supraorbital nerve was studied in 14 cases of intrinsic brain stem lesions (2 mesencephalic, 6 pontine, and 4 medullary neoplasms, and 2 pontine syrinxes) and 20 cases of lesions extrinsic to the brain stem (6 cerebellar and 14 cerebellopontine angle tumors). The early reflex was abnormal in all but three cases of medullary tumors and one case of cerebellar tumor. Alteration of the early reflex by posterior fossa tumors reflects either delayed conduction through the pons due to intrinsic pontine lesions or extrinsic compression of the pons, or indicates trigeminal or facial nerve involvement by tumor. The late reflex with its direct and consensual components is useful in distinguishing afferent from efferent delay (or block). Mixed patterns suggest combined involvement of the trigeminal and facial nerves or a relatively widespread brain-stem lesion. This simple technique appears to be a useful addition to clinical observation in assessment of posterior fossa tumors.

Visual evoked responses in patients with multiple sclerosis

The visual evoked response (VER) was evaluated in a series of multiple sclerosis patients and normal subjects. The data showed significant delays in wave peak latencies among the patient evoked responses. The prolonged latencies correlated closely with visual impairment; however, even patients with a previous history of visual impairment, but with no deficits noticeable on examination at the time of study, showed a delay in wave peak latencies. The results further suggest that the VER is primarily altered when there are central field defects.

Orbicularis oculi reflex in coma: clinical, electrophysiological, and pathological correlations

The orbicularis oculi reflex was studied in 48 comatose patients and the results were correlated with clinical and pathological findings. The late component of the reflex was absent or of minimal amplitude in all cases regardless of the site of lesions, reflecting a diffuse suppression of the reticular system rather than a specific or local block in the brain-stem. Alteration of the early component of the reflex, on the other hand, generally indicated primary or secondary structural changes in the pons, although reversible functional or pharmacological block of pontine conduction was also documented.

Orbicularis oculi reflex in the Wallenberg syndrome: alteration of the late reflex by lesions of the spinal tract and nucleus of the trigeminal nerve

The orbicularis oculi reflex was studied in nine cases with lateral medullary lesions. Diagnosis of the Wallenberg syndrome was made clinically in seven cases and at necropsy in another. The clinical features of one other case were closely allied to but not typical of this syndrome. An afferent delay of the late reflex on the side of the lesion in the presence of a normal early reflex was seen in all but two cases. In one of the latter, the late reflex was normal and in the other, a comatose patient, the late reflex was totally absent. It was concluded that the neurones of the first order responsible for the bilateral late reflex on unilateral stimulation terminate in the ipsilateral spinal nucleus of the trigeminal nerve without significant crossing over to the same structure on the other side. An afferent delay of the late reflex in the presence of a normal or nearly normal early reflex is consistent with a lateral medullary lesion implicating the spinal tract and nucleus. The Wallenberg syndrome is a common clinical entity showing this abnormality of the orbicularis oculi reflex.