Abnormal Vestibular Evoked Myogenic Potentials in Medial Medullary Infarction

Background

The medial vestibulospinal tract (MVST), which descends in the medial longitudinal fasciculus (MLF), may mediate the vestibular evoked myogenic potentials (VEMPs) in the contracting sternocleidomastoid muscle. We report herein abnormal VEMPs in a patient with medial medullary infarction (MMI) that appeared to involve the MLF.

Case Report

A patient with infarction involving the right medial medulla showed decreased p13-n23 amplitude and increased p13/n23 latencies of the VEMPs on the right side. These abnormal VEMPs recorded in an MMI patient support the theory that VEMPs are mediated by the MVST contained within the MLF.

Conclusions

VEMPs may represent a valuable tool for investigating vestibular dysfunction originating from the saccule, even in patients with central vestibulopathies, which is not readily defined by conventional vestibular function tests.     

Primary Position Upbeat Nystagmus during an Acute Attack of Multiple Sclerosis

Background and Purpose

Ocular manifestation is one of the frequent signs of an acute attack in multiple sclerosis (MS), although primary position upbeat nystagmus (PPUN) is rare. The purpose of this study is to determine the incidence of PPUN in MS and to determine the lesions that are responsible for this sign.

Methods

The medical records of 120 MS patients with acute brain lesions were reviewed over a consecutive period of 9 years; of these, 6 patients were found to have PPUN. Other ocular motor abnormalities were analyzed in combination with upbeat nystagmus, video-oculographic findings, and lesions detected on brain MRI.

Results

Lesions in the pontine tegmentum involving the medial longitudinal fasciculus (MLF) and ventral tegmental tract (VTT) were the most common, being observed in three of the six patients with PPUN. One patient exhibited caudal medullary lesions bilaterally affecting the paramedian portion of the posterior tegmentum, and two patients exhibited multiple lesions involving the pons with the cerebral peduncle or medulla. In five patients, other ocular motor dysfunctions, such as gaze-evoked nystagmus (n=3) and internuclear ophthalmoplegia (n=1), were found in combination with upbeat nystagmus.

Conclusions

PPUN is an infrequent, ocular manifestation noted during an acute attack of MS, and was observed in 5% of the present cases. Brainstem lesions in these cases primarily involved the pontine tegmentum and the caudal medulla. These findings support the theory that upbeat nystagmus is attributable to damage to the upward vestibulo-ocular reflex pathway related to the vestibular nucleus, VTT, and interconnecting pathways.     

Lateral Medullary Syndrome Following Injury of Lateral Vestibulospinal Tract: Diffusion Tensor Imaging Study

BackgroundUnilateral lesions of vestibular nucleus can cause lateral medullary syndrome. Little is known about injury of medial and lateral vestibulospinal tract (VST) after dorsolateral medullary infarct. We investigated injury of the lateral VST in patients with typical central vestibular disorder using diffusion tensor tractography (DTT).MethodsSeven patients with lateral medullary syndrome and ten control subjects were recruited. For the medial VST, we determined seed region of interest (ROI) as medial vestibular nuclei of pons and target ROI on posteromedial medulla. For the lateral VST, the seed ROI was placed on lateral vestibular nuclei of pons, and the target ROI on posterolateral medulla. Fractional anisotropy (FA), mean diffusivity (MD), and tract volume were measured.ResultReconstructed lateral VST on both sides had significantly lower FA values in patients than controls (p<0.05). Tract volume of lateral VST in affected side was significantly lower than unaffected side and control group (p<0.05). However, no DTI parameters of the medial VST differed between patients and controls (p>0.05).ConclusionInjury of the lateral VST was demonstrated in patients with lateral vestibular syndrome following dorsolateral medullary infarct. Analysis of the lateral VST using DTT would be helpful in evaluation of patients with lateral medullary syndrome.     

Medial medullary infarction: abnormal ocular motor findings

In 20 consecutive patients with isolated medial medullary infarction, abnormal ocular motor findings included nystagmus (n = 8), ocular contrapulsion (n = 5), and contralesional ocular tilt reaction (n = 2). The nystagmus was ipsilesional (n = 4), gaze-evoked (n = 5), upbeating (n = 4), and hemiseesaw (n = 1). The ocular motor abnormalities may be explained by involvements of the nucleus prepositus hypoglossi, medial longitudinal fasciculus or efferent fibers from the vestibular nuclei, climbing fibers, and cells of the paramedian tracts.     

31例延髓梗死患者的临床分析

目的:根据头颅MRI对延髓梗死病灶的定位并结合延髓的解剖学特点,探讨延髓梗死临床表现的特征.方法:31例急性延髓梗死患者均行头颅MRI检查,对其病灶位置分布、神经系统症状体征,出院当天改良Rankin量表(mRS)评分等指标进行分析.结果:31例急性延髓梗死病例中:外侧延髓梗死(LMI)16例;内侧延髓梗死(MMI)13例;双侧延髓梗死(BMI)2例.LMI组病灶位于延髓背外侧或外侧;MMI组病灶位于延髓腹内侧,且多位于延髓上段.LMI多表现为不典型或部分性的"Wallenberg综合征",最常见的症状或体征为眩晕,Homer征、构音障碍、吞咽障碍、软腭麻痹,肢体共济失调.MMI多表现为感觉运动性卒中(SMS)或纯运动性卒中(PMS),最常见的症状或体征为对侧肢体偏瘫、构音障碍、中枢性面舌瘫.31例延髓梗死患者中,BMI 2例均为双侧MMI,其中1例出现四肢瘫痪、双侧肢体深浅感觉障碍、核间性眼肌麻痹、构音以及吞咽障碍,另1例表现为左侧肢体偏瘫、构音障碍、强哭、强笑等症状体征.结论:典型的延髓梗死综合征在临床上少见,LMI多表现为不典型,部分性的"Wallenberg综合征".而MMI往往与桥脑、基底节区腔隙性梗死的临床表现相似.双侧MMI导致四肢瘫痪等双侧锥体束受损表现,预后较差.     

Impaired Tilt Suppression of Post-Rotatory Nystagmus and Cross-Coupled Head-Shaking Nystagmus in Cerebellar Lesions: Image Mapping Study

We sought to determine the cerebellar structures responsible for tilt suppression of post-rotatory nystagmus. We investigated ocular motor findings and MRI lesions in 73 patients with isolated cerebellar lesions who underwent recording of the vestibulo-ocular reflex (VOR) using rotatory chair tests. Tilt suppression of post-rotatory nystagmus was diminished in 27 patients (27/73, 37.0 %). The gains of the VOR and the TCs of per- and post-rotatory nystagmus did not differ between the patients with diminished and with normal tilt suppression. The patients with impaired tilt suppression showed perverted (“cross-coupled”) head-shaking nystagmus (pHSN) and central positional nystagmus (CPN) more frequently than those with normal responses. Tilt suppression was impaired in five (71.4 %) of the seven patients with isolated nodulus and uvular infarction. Probabilistic lesion-mapping analysis showed that the nodulus and uvula are responsible for tilt suppression. Impaired tilt suppression may be ascribed to disruption of cerebellar contribution to the vestibular velocity-storage mechanism, which integrates information from the semicircular canals and otolith organs to help derive the brain’s estimate of the head orientation relative to the pull of gravity.     

Inferior vestibular neuritis

Vestibular neuritis (VN) mostly involves the superior portion of the vestibular nerve and labyrinth. This study aimed to describe the clinical features of VN involving the inferior vestibular labyrinth and its afferents only. Of the 703 patients with a diagnosis of VN or labyrinthitis at Seoul National University Bundang Hospital from 2004 to 2010, we retrospectively recruited 9 patients (6 women, age range 15-75) with a diagnosis of isolated inferior VN. Diagnosis of isolated inferior VN was based on torsional downbeating spontaneous nystagmus, abnormal head-impulse test (HIT) for the posterior semicircular canal (PC), and abnormal cervical vestibular-evoked myogenic potentials (VEMP) in the presence of normally functioning horizontal and anterior semicircular canals, as determined by normal HIT and bithermal caloric tests. All patients presented with acute vertigo with nausea, vomiting, and imbalance. Three patients also had tinnitus and hearing loss in the involved side. The rotation axis of torsional downbeating spontaneous nystagmus was best aligned with that of the involved PC. HIT was also positive only for the involved PC. Cervical VEMP was abnormal in seven patients, and ocular VEMP was normal in all four patients tested. Ocular torsion and subjective visual vertical tests were mostly within the normal range. Since isolated inferior VN lacks the typical findings of much more prevalent superior VN, it may be mistaken for a central vestibular disorder. Recognition of this rare disorder may help avoid unnecessary workups in patients with acute vestibulopathy.     

Sensory sequelae of medullary infarction: differences between lateral and medial medullary syndrome

BACKGROUND AND PURPOSE: A comparison between long-term sensory sequelae of lateral medullary infarction (LMI) and medial medullary infarction (MMI) has never been made. METHODS: We studied 55 patients with medullary infarction (41 with LMI and 14 with MMI) who were followed up for >6 months. We examined and interviewed the patients with the use of a structured format regarding the most important complaints, functional disabilities, and the presence of sensory symptoms. The nature and the intensity of sensory symptoms were assessed with the modified McGill-Melzack Pain Questionnaire and the visual analog scale, respectively. RESULTS: There were 43 men and 12 women, with an average age of 59 years. Mean follow-up period was 21 months. The sensory symptoms were the most important residual sequelae in LMI patients and the second most important in MMI patients. In LMI patients, the severity of residual sensory symptoms was significantly related to the initial severity of objective sensory deficits (P<0.05). Sensory symptoms were most often described by LMI patients as numbness (39%), burning (35%), and cold (22%) in the face, and cold (38%), numbness (29%), and burning (27%) in the body/limbs, whereas they were described as numbness (60%), squeezing (30%) and cold (10%), but never as burning, in their body/limbs by MMI patients. LMI patients significantly (P<0.05) more often cited a cold environment as an aggravating factor for the sensory symptoms than did the MMI patients without spinothalamic sensory impairment. The subjective sensory symptoms were frequently of a delayed onset (up to 6 months) in LMI patients, whereas they usually started immediately after the onset in MMI patients. CONCLUSIONS: Our study shows that sensory symptoms are major sequelae in both LMI and MMI patients. However, the nature, the mode of onset, and aggravating factors are different between the 2 groups, which probably is related to a selective involvement of the spinothalamic tract by the former and the medial lemniscus by the latter. We suggest that the mechanisms for the central poststroke pain or paresthesia may differ according to the site of damages on the sensory tracts (spinothalamic tract versus medial lemniscal tract).     

Medial medullary infarction: report of three patients presented with central vestibular dysfunction without limb and lingual weakness]

The purpose of this article is to draw attention to atypical presentation of medial medullary infarction (MMI). With advanced imaging techniques, small infarctions occurring in the medulla are more easily identified. It is difficult, however, to make a clinical diagnosis of MMI if both hypoglossal nerve palsy and limb weakness are absent, because motor weakness is considered a cardinal manifestation of MMI. We describe here three patients who developed central vestibular dysfunction due to MMI without limb and lingual weakness. Case 1: A 44-year-old, diabetic woman developed vomiting and numbness on her left upper limb. Examination revealed unidirectional horizontal and rotatory nystagmus beating toward the right side. There were no Horner syndrome and hypoglossal nerve palsy. Barré arm and leg signs and limb ataxia were absent. Romberg sign was negative. Hypesthesia was present on her left forearm, hand, and fingers. Thumb-localizing test was normal. Cranial MRI demonstrated an infarction in the right paramedian region of the upper medulla. MR angiography demonstrated irregularity of the basilar and the left vertebral arteries. Case 2: A 69-year-old woman suffered from dizziness and nausea. She showed unidirectional, left-beating horizontal nystagmus. There were no Horner syndrome and hypoglossal nerve palsy, Barré arm and leg signs, and limb ataxia. MRI disclosed an infarction in the left upper medial medulla. Case 3: A 47-year-old man developed vertigo when turning over in bed. He showed left-beating nystagmus without latency, when lying down. Horner syndrome and hypoglossal nerve palsy were absent MRI showed bilateral MMI, with the right lesion being larger than the left. MR angiography demonstrated a stenosis in the distal portion of the left internal carotid artery but not in the vertebral and basilar arteries and their branches. This case represents central positional vertigo. Vestibular syndrome seen in cases 1 and 2 was incomplete and incongruent, suggesting dysfunction of the central vestibular system. There have been only nine cases of MMI with horizontal nystagmus in primary position, including unidirectional horizontorotatory nystagmus. In these cases, horizontal nystagmus beats toward the side of the lesion. In sharp contrast, horizontal nystagmus typically beats away from the lesion side in cases of Wallenberg syndrome, suggesting different underlying mechanism. Unidirectional horizontal and rotatory nystagmus is generally associated with peripheral vestibular dysfunction. There has been no reported case of MMI presenting with vestibular dysfunction preserving motor power. Thus, this "benign" form of MMI might have been misdiagnosed as peripheral vestibular dysfunction before the era of MRI.     

Impaired Modulation of the Otolithic Function in Acute Unilateral Cerebellar Infarction

To define the cerebellar contribution in modulating the otolithic signals, we investigated the otolithic function in 27 patients with acute unilateral cerebellar infarctions in the territory of the posterior inferior cerebellar artery (PICA, n?=?17, 63 %), combined PICA and superior cerebellar artery (SCA) (n?=?7, 30 %), SCA (n?=?2, 7 %), and anterior inferior cerebellar artery (n?=?1, 4 %) from 2010 to 2012. The patients had evaluation of the ocular tilt reaction [head tilt, ocular torsion (OT), and skew deviation], tilt of the subjective visual vertical (SVV), cervical vestibular evoked myogenic potentials (VEMPs) in response to air conducted tone bursts, and ocular VEMPs induced by tapping the head at AFz. The evaluation was completed within 2 weeks after symptom onset. Patients often showed OT or SVV tilt (15/27, 55.6 %) that was either ipsi- (n?=?6) or contraversive (n?=?9). Overall, there were no differences in the amplitudes and latencies of cervical and ocular VEMPs between the ipsi- and contralesional sides. However, individual analyses revealed frequent abnormalities of cervical (11/27, 41 %) and/or ocular (9/27, 33 %) VEMPs. While 11 (73 %) of the 15 patients with the OTR/SVV tilt showed abnormalities of cervical (n?=?9) and/or ocular (n?=?7) VEMP responses, only three (25 %) of the 12 patients without the OTR/SVV tilt had abnormal cervical (n?=?2) and/or ocular (n?=?2) VEMPs (73 % vs. 25 %, Fisher’s exact test, p?=?0.021). The concordance rate in the results of cervical and ocular VEMPs was marginally significant (19/27, 70 %, p?=?0.052, binominal). Unilateral cerebellar lesions may generate otolithic imbalances, as evidenced by the OTR/SVV tilt and asymmetric ocular or cervical VEMP responses, but without directionality according to the lesion side. Patients with the OTR/SVV tilt had abnormal VEMPs more often than those without.     

Bowtie and upbeat nystagmus evolving into hemi-seesaw nystagmus in medial medullary infarction: possible anatomic mechanisms

A 20-year-old man with bilateral medial medullary infarction showed transition of bowtie and upbeat nystagmus into hemi-seesaw nystagmus. Follow-up MRI revealed near complete resolution of the right medullary lesion. This transition of nystagmus suggests that the upbeat nystagmus was generated by bilateral lesions in the ascending pathways from both anterior semicircular canals (SCC), and that the hemi-seesaw nystagmus was caused by damage to the pathway from the left anterior SCC.     

Acquired pendular nystagmus in multiple sclerosis: clinical observations and the role of optic neuropathy.

Thirty seven patients with pendular nystagmus due to multiple sclerosis were reviewed. Most developed nystagmus later in a progressive phase of the disease. All had cerebellar signs on examination and evidence of optic neuropathy. MRI in eight patients showed cerebellar or brainstem lesions in seven; the most consistent finding was a lesion in the dorsal pontine tegmentum. Dissociated nystagmus was seen in 18 patients: in these the signs of optic neuropathy were often asymmetric and the severity correlated closely with the side with larger oscillations. This suggests that dissociations in acquired pendular nystagmus may be due to asymmetries in optic neuropathy rather than asymmetries in cerebellar or brainstem disease.     

Head tilt produced by hemilabyrinthectomy does not depend on the direct vestibulospinal tracts

Head tilt is one of the most characteristic and enduring symptoms produced by hemilabyrinthectomy and is compensated by the central nervous system with time. In order to study the central mechanisms of compensation of the head tilt, it is first necessary to understand how it is produced. However, its mechanism remains unknown. Experiments were performed in cats to examine whether the direct vestibulocollic pathways are responsible for the head tilt, as suggested by some authors. Hemilabyrinthectomies produced a characteristic head tilt in cats in which the medial and/or one lateral vestibulospinal tracts (VSTs) had been interrupted. The lesions of the medial VST did not influence the preexisting head tilt produced by hemilabyrinthectomies. These results suggest that the head tilt produced by hemilabyrinthectomies does not depend on the activity of the VSTs.     

HORIZONTAL OPTOKINETIC NYSTAGMUS IN CEREBRAL DISEASES

Among 6377 examinations for optokinetic nystagmus we, found 142 patients exhibiting abnormal horizontal optokinetic nystagmus. This is 14 % of the approx. 1000 patients with confirmed organic lesion of the central nervous system. In 40 patients the optokinetic nystagmus was abnormal (absent and/or defective) to both sides, in 102 to one side. Unilaterally abnormal optokinetic nystagmus was found in 46 patients with supratentorial lesions such as thrombosis, infarcts, haematomas, and tumours affecting the posterior part of the hemisphere or of a deep hemispheric site, usually in the temporo-parietal lobe. In 20 cases optokinetic nystagmus was absent, in 26 defective, but in all 46 cases it was abnormal to the side opposite that of the lesion. In 40 patients with infratentorial lesions, usually infarcts or tumours in the cerebello-pontine angle and in the brain stem, the optokinetic nystagmus to the side of the lesion was absent in 21, defective in 19, including 16 to the homolateral and 3 to the contralateral side. Unilaterally abnormal optokinetic nystagmus is of great value in locating the side of the lesion, and this applies to supra- as well as infratentorial lesions. Among 40 patients with bilaterally abnormal optokinetic nystagmus, we found most often lesions high in the brain stem and mesencephalon. However, 7 patients had predominantly cerebral signs, but in these cases the mesencephalon was involved as well. Provided that cooperation is good, a bilaterally abnormal optokinetic nystagmus indicates involvement of the pons or mesencephalon. Homonymous hemianopia and an abnormal optokinetic nystagmus to the same side, found in 20 cases of the present material, indicate involvement of the parietal lobe. The investigation fully confirms Cord's hypothesis and shows a great certainty of abnormal horizontal optokinetic nystagmus in the topographic diagnosis of diseases of the central nervous system.     

Topodiagnostic investigations on the sympathoexcitatory brain stem pathway using a new method of three dimensional brain stem mapping

OBJECTIVES: To study the incompletely understood sympathoexcitatory pathway through the human brain stem, using a new method of three dimensional brain stem mapping on the basis of digitally postprocessed magnetic resonance imaging (MRI). METHODS: 258 consecutive patients presenting with acute signs of brain stem ischaemia underwent biplane T2 and EPI diffusion weighted MRI, with slice orientation parallel and perpendicular to a transversal slice selection of the stereotactic anatomical atlas of Schaltenbrand and Wahren, 1977. The individual slices were digitally normalised and projected onto the appropriate slices of the anatomical atlas. For correlation analysis lesions were imported into a three dimensional model of the human brain stem. RESULTS: 31 of the 258 patients had Horner's syndrome caused by acute brain stem ischaemia. Only four of the patients with Horner's syndrome had pontine infarctions, 12 had pontomedullary lesions, and 15 had medullary lesions. Correlation analysis showed significantly affected voxels in the dorsolateral medulla but not in the pons. A statistical comparison with infarct topology in patients with medullary lesions but without Horner's syndrome indicated that involvement of the medial and ventral part of affected voxels located in the ventrolateral medullary tegmentum was specific for Horner's syndrome. CONCLUSIONS: Based on this first in vivo topodiagnostic study, the central sympathoexcitatory pathway probably descends through the dorsal pons before converging on specific generators in the ventrolateral medullary tegmentum at a level below the IX and X nerve exits.     

Localizing value of torsional nystagmus in small midbrain lesions

BACKGROUND: The topodiagnostic value and specificity of nystagmus in patients with mesencephalic lesions and its relation to tonic torsional deficits and vertical saccade deficits is controversial and anecdotal. METHODS: The authors examined 11 patients with vascular MRI-identified mesencephalic lesions and clinical evidence of vertical-torsional nystagmus on gaze straight ahead, focusing on the three-dimensional nystagmus components recorded with the three-dimensional search coil technique. RESULTS: Combined lesions of the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF) and the interstitial nucleus of Cajal (iC) are much more frequent than riMLF and, in particular, iC lesions alone. Eight patients showed contralesional torsional nystagmus with a conjugate vertical component on gaze straight ahead and had anatomic (MRI) and clinical evidence (slowing of vertical saccades) for riMLF involvement. Tonic ocular torsion and the subjective visual vertical were shifted to the contralesional side (n = 7). Torsional nystagmus to the ipsilesional side was uncommon (n = 3) and found in patients with midbrain lesions involving the iC, all of whom also had decreased time constants of the slow phases of gaze-evoked nystagmus. CONCLUSIONS: Contrary to previous proposals, contralesional torsional nystagmus was the most frequent direction and is probably not compensatory for contralesional tonic ocular torsion. Small amplitude vertical saccades with normal velocities in association with ipsilesional torsional nystagmus may indicate isolated iC lesions. Torsional nystagmus following mesencephalic lesions may last for years and may help to distinguish rostral (riMLF) from caudal (iC) midbrain lesions.     

Spectrum of medial medullary infarction: clinical and magnetic resonance imaging findings

Among 4200 consecutive patients admitted to three hospitals with acute ischemic stroke, we found only 11 patients in whom magnetic resonance imaging (MRI) had proved that they had medial medullary infarction (MMI). In our centers, patients with MMI were less than 1 % of those with vertebrobasilar stroke. The infarcts documented by MRI were unilateral in 10 patients and bilateral in one. On clinico-topographical analysis there were four clinical patterns: (1) Classical Dejerine's syndrome was the most frequent, consisting of contralateral hemiparesis, lemniscal sensory loss and ipsilateral lingual palsy in 7 of the eleven patients. (2) Pure hemiparesis was present in 2 patients; (3) Sensorimotor stroke was present in 1 patient with contralateral hemiparesis, hypesthesia and mild decrease in pain sensation without lingual palsy; (4) Bilateral MMI syndrome in 1 patient, accompanied by tetraparesis, bilateral loss of deep sensation, dysphagia, dysphonia and anarthria. Presumed causes of MMI were intrinsic branch penetrator artery disease with concomitant vertebral artery stenosis in 6 of the 11 patients, vertebral artery occlusion in 2, dolichoectatic vertebrobasilar arteries in 2, a source of cardiac embolism in 1. Prognosis at 3 months was favorable in 8 patients, but the patient with bilateral MMI syndrome had persisting motor deficit causing limitation of daily activities, and 2 died from systemic causes. The classical triad of acute MMI facilitates the diagnosis, although the recognition of this syndrome in patients with incomplete manifestations can be difficult and occurs more frequently than commonly thought. Moreover, vertebral artery atherosclerosis and branch atheromatous disease of the penetrating arteries are the main causes of medullary infarction. Received: 21 February 2001, Received in revised form: 22 February 2001, Accepted: 17 May 2001     

VERTICAL OPTOKINETIC NYSTAGMUS

Among 6377 investigations for optokinetic nystagmus the authors found 97 patients with abnormal vertical optokinetic nystagmus and normal horizontal optokinetic nystagmus. This is 10 % of the approx. 1000 patients with manifest organic lesion of the central nervous system. In 30 the vertical optokinetic nystagmus was abnormal in one direction, in 67 cases in both. Abnormality of the vertical optokinetic nystagmus in both directions was found in unilateral cerebral lesions, unilateral brain-stem lesions, and in more diffuse lesions of the central nervous system. Total absence of vertical optokinetic nystagmus was observed in only 7 patients, 5 of whom had vertical gaze paralysis, 4 of them due to pseudobulbar paralysis. Abnormality of the vertical optokinetic nystagmus in both directions in cases with definitely unilateral signs from the cerebrum or mesencephalon indicates that both vertical gaze centres have to function simultaneously to elicit normal optokinetic nystagmus. This is also confirmed by the fact that the severity of the abnormal vertical optokinetic nystagmus is greatest in lesions high in the mesencephalon, where the paths for vertical optokinetic nystagmus assemble in the two vertical gaze centres. Abnormality of the vertical optokinetic nystagmus as an isolated finding is interpreted as a sign of organic disease in the central nervous system and should lead to further special investigations for a more detailed diagnosis.     

Upbeat nystagmus: clinicopathological and pathophysiological considerations.

We describe an electro-oculographic study of upbeat nystagmus in 4 patients, with neuropathological correlation in one. All patients had lesions in the pontine tegmentum. The electro-oculographic data may be explained by imbalanced vertical vestibular or smooth pursuit eye movement control. The nystagmus stopped or reversed direction during convergence or in supine head positions. We propose that changes in the intensity or direction of upbeat nystagmus that are induced by convergence or changes in head position, are caused by vertical imbalance in the otolithic-ocular reflex, when superimposed on an imbalanced vestibulo-ocular reflex (VOR). Imbalance of the otolithic-ocular reflex and the vertical VOR are caused by damage in the pontomedullary tegmentum.     

The somatosensory blink reflex in upper and lower brainstem lesions

The brainstem pathways that mediate the somatosensory blink reflex (SBR) are not completely understood. We hypothesized that the circuits of the SBR might be affected separately from those of the trigeminal blink reflex (TBR). We examined 7 patients with mesencephalic lesions and 8 patients with medullary lesions. The SBR was elicited by median nerve stimulation. The TBR was elicited by supraorbital nerve stimulation. In patients with upper brainstem lesions, the TBR was normal, whereas the SBR was generally abnormal. The SBR was either absent or small and was significantly delayed with respect to control subjects. The opposite was the rule in patients with lower brainstem lesions who had delayed or absent TBR and no abnormal findings in the SBR. The SBR is mediated through circuits in the upper brainstem. Study of the SBR can be helpful in the neurophysiological assessment of patients with mesencephalic lesions.