Spontaneous Downbeat Nystagmus Research Articles

A case of vertebrobasilar dolichoectasia manifesting as sudden sensorineural hearing loss with vertigo

Vertebrobasilar dolichoectasia (VBD) is a rare vascular condition characterized by the elongation, widening, and tortuosity of the vertebrobasilar artery. It can lead to various symptoms due to compression of cranial nerves and brainstem structures. We report a rare case of VBD presenting as sudden sensorineural hearing loss (SSNHL) with vertigo and spontaneous downbeat nystagmus in a 65-year-old woman with a history of hypertension. Magnetic resonance imaging revealed a tortuous and dilated right vertebrobasilar artery compressing the brainstem and left 8th cranial nerve root entry zone, without signs of acute cerebellar stroke. The compression of the anterior inferior cerebellar artery and cervicomedullary junction was also noted, suggesting a vascular cause for her symptoms. Following high-dose steroid treatment, the patient showed significant hearing improvement. This case underscores the importance of considering VBD in patients with unexplained SSNHL and vertigo, highlighting the role of detailed vascular imaging in the diagnosis and management of such cases.

Analysis of etiology and clinical features of spontaneous downbeat nystagmus: a retrospective study.

To investigate the topical diagnosis, possible etiology and mechanism of spontaneous downbeat nystagmus (sDBN) patients with dizziness/vertigo. The clinical features of dizziness/vertigo patients accompanied with DBN were retrospectively reviewed in the Vertigo Center of our hospital from January 2018 to March 2021. The clinical features of dizziness/vertigo patients accompanied with DBN were reviewed. Comprehensive VNG, bithermal caloric testing, video-head-impulse test (vHIT), vestibular-evoked myogenic potentials (VEMP), head magnetic resonance imaging (MRI), three-dimensional fluid-attenuated incersion recovery magnetic resonance imaging (3D-FLAIR MRI) in the inner ear, serum immunology and other examinations were to determine the lesion site, and analyze its possible etiology and mechanism. A total of 54 patients were included. Among them, 70.4% (n = 38) of DBN patients were diagnosed with episodic vestibular syndrome (EVS), 22.2% (n = 12) with chronic vestibular syndrome (CVS), and 7.4% (n = 4) with acute vestibular syndrome (AVS). Among all the patients, 51.9% of DBN patients had clear etiology, with central lesions of 29.6% and peripheral diseases of 22.2%. The most common diseases in DBN patients were cerebellar lesions (13.0%, n = 7) and vestibular migraine (13.0%, n = 7), followed by benign positional paroxysmal vertigo (7.4%, n = 4) and drug-related dizziness/vertigo (5.6%, n = 3). The other 48.1% of the patients had unknown etiology. 53.8% (14/26) of patients with idiopathic DBN had decreased semicircular canal function, with 42.9% (6/14) decreased posterior semicircular canal function. The posterior semicircular canal gain in DBN patients decreased compared to the anterior semicircular canal in the same conjugate plane. Patients with peripheral DBN were more prone to horizontal/torsional nystagmus during positional testing. In our study, DBN patients have a relative decrease in posterior semicircular canal gain, which is possibly a particular result found in a subset of downbeat nystagmus patients. The changes in nystagmus during positional testing may be helpful in distinguishing between peripheral and central causes.

Speech, Gait, and Vestibular Function in Cerebellar Ataxia with Neuropathy and Vestibular Areflexia Syndrome.

(1) Background: Cerebellar ataxia with neuropathy and vestibular areflexia syndrome (CANVAS) is characterized by late-onset cerebellar ataxia, bilateral vestibulopathy, and sensory neuronopathy mostly due to biallelic RFC1 expansion. (2) Objectives: The aim of this case series is to describe vestibular, gait, and speech alterations in CANVAS via a systematic approach. (3) Methods: All patients (n = 5) underwent a standardized clinical-instrumental examination, including the perceptual and acoustic analysis of speech, instrumental gait, and balance analysis (posturographic data were acquired using a force plate [Kistler, Winterthur, Switzerland] while 3D gait analysis, inclusive of surface electromyography, was acquired using a motion capture system [SMART DX, BTS Bioengineering, Milan, Italy], a wireless electromyograph [FreeEMG, BTS Bioengineering, Milan, Italy]), and vestibular assessment with video-oculography. (4) Results: Five patients were included in the analysis: three females (patients A, B, C) and two males (patients D and E) with a mean age at evaluation of 62 years (SD ± 15.16, range 36-74). The mean age of symptoms' onset was 55.6 years (SD ± 15.04, range 30-68), and patients were clinically and instrumentally evaluated with a mean disease duration of 6.4 years (SD ± 0.54, range 6-7). Video-Frenzel examination documented spontaneous downbeat nystagmus enhanced on bilateral gaze in all patients, except for one presenting with slight downbeat nystagmus in the supine position. All patients exhibited different degrees of symmetrically reduced VOR gain for allsix semicircular canals on the video-head impulse test and an unexpectedly normal ("false negative") VOR suppression, consistent with combined cerebellar dysfunction and bilateral vestibular loss. Posturographic indices were outside their age-matched normative ranges in all patients, while 3D gait analysis highlighted a reduction in ankle dorsiflexion (limited forward rotation of the tibia over the stance foot during the stance phase of gait and fatigue of the dorsiflexor muscles) and variable out-of-phase activity of plantar flexors during the swing phase. Finally, perceptual-acoustic evaluation of speech showed ataxic dysarthria in three patients. Dysdiadochokinesis, rhythm instability, and irregularity were observed in the oral diadochokinesis task. (5) Conclusions: CANVAS is a recently discovered syndrome that is gaining more and more relevance within late-onset ataxias. In this paper, we aimed to contribute to a detailed description of its phenotype.

Vestibular seizures and spontaneous downbeat nystagmus of ganglioglioma origin: a case report

BackgroundLow-grade gangliogliomas (GGs) are typically epileptogenic intracranial neoplasms. Yet, the presentation of simplex vertiginous experience and spontaneous downbeat nystagmus (DBN) has not been reported to date.Case presentationWe present the case of a 26-year-old male with focal onset impaired awareness seizures, characterized by vertigo due to right temporal lobe epilepsy caused by ganglioglioma. As rare presentations, a spontaneous, consistent DBN in the absence of vertiginous experience was noticed. MRI suggested lesion in the right temporal pole. Twenty-four-hour continuous electroencephalogram (EEG) monitoring recorded periodic sharp and slow waves, originating from the right temporal lobe. The patient was completely relieved of the symptoms after surgical removal of the tumor, which was histologically confirmed as Grade I Ganglioglioma.ConclusionsAsides from the cortical pathogenesis of epileptic vertigo, this case also provides insight into the DBN secondary to tumor of the temporal lobe. Moreover, the 24-h EEG is advantageous to recognize vestibular seizures and localize the ictal onset areas.

Cardiogenic vertigo: characteristics and proposed diagnostic criteria.

Early identification of cardiogenic vertigo (CV) is necessary to prevent serious complications of cardiovascular diseases. However, the literature is limited to case reports without detailed clinical features or diagnostic criteria. The aim of this study was to define characteristics of CV and propose diagnostic criteria. This study included patients with CV diagnosed at Pusan National University and Keimyung University Hospitals. Demographic, clinical, laboratory, and treatment data were analyzed. Of 72 patients with clinically suspicious CV, 27 were finally included. The age ranged from 63 to 88years (75.1 ± 7.2years). Recurrent vertigo occurred without syncopal attacks in 52% [95% CI, 32-71], while it preceded (37% [19-58]) or followed (11% [2-29]) syncope. The patients with recurrent isolated vertigo had suffered from symptoms from 15days to 5years until final diagnosis (median 122days). The vertigo lasted only for a few seconds (93% [76-99]) or a few minutes (7% [1-24]). Fourteen patients presented with spinning vertigo, and one of them showed spontaneous downbeat nystagmus during the attack. Accompanying symptoms including chest discomfort, palpitation, headache, arm twitching, and lightheadedness were found in 70% [50-86]. Between patients with and without syncope, there was no difference in clinical parameters and results of cardiac function tests. The most common cardiac abnormality during the attacks of vertigo was bradyarrhythmia (89% [71-98]). Cardiovascular diseases can develop recurrent isolated vertigo without or preceding syncope. Onset age, duration of vertigo, accompanying symptoms, and underlying cardiac diseases can aid in differentiation from other vestibular disorders. Early identification of CV would reduce morbidity and mortality associated with cardiac syncope.

Ictal downbeat nystagmus in Ménière disease: A cross-sectional study.

To determine the mechanism of ictal downbeat nystagmus in Ménière disease (MD), we compared the head impulse gain of the vestibulo-ocular reflex (VOR) for each semicircular canal between patients with (n = 7) and without (n = 70) downbeat nystagmus during attacks of MD. We retrospectively analyzed the results of video-oculography, video head-impulse tests, and cervical vestibular-evoked myogenic potentials (VEMPs) in 77 patients with definite MD who were evaluated during an attack. Pure or predominant downbeat nystagmus was observed in 7 patients (9%) with unilateral MD during the attacks. All 7 patients showed spontaneous downbeat nystagmus without visual fixation with a slow phase velocity ranging from 1.5 to 11.2°/s (median 5.4, interquartile range 3.7-8.5). All showed a transient decrease of the head impulse VOR gains for the posterior canals (PCs) in both ears (n = 4) or in the affected ear (n = 3). Cervical VEMPs were decreased in the affected (n = 2) or both ears (n = 2) when evaluated during the attacks. Downbeat nystagmus disappeared along with normalization of the VOR gains for PCs after the attacks in all patients. During the attacks, the head impulse VOR gains for the PC on the affected side were lower in the patients with ictal downbeat nystagmus than in those without (Mann-Whitney U test, p < 0.001), while the gains for other semicircular canals did not differ between the groups. Downbeat nystagmus may be observed during attacks of MD due to an asymmetry in the vertical VOR or saccular dysfunction. MD should be considered in recurrent audiovestibulopathy and ictal downbeat nystagmus.

It is not your eyes

A 55-year-old woman reported blurred vision while walking, numbness and tingling, contact allodynia, and gait imbalance. Visual acuity was 20/20 in both eyes, but there was a loss of 4 lines with horizontal dynamic visual acuity testing. Ocular motility examination demonstrated spontaneous downbeat nystagmus that increased in lateral gaze with a torsional component and impaired smooth pursuits. Head impulse test was positive, and electromyography demonstrated a sensory neuropathy/neuronopathy. Vestibular testing confirmed both central ocular motor pathway and bilateral peripheral vestibular system involvement. The constellation of clinical findings and paraclinical testing was consistent with a recently recognized neurodegenerative disorder termed cerebellar ataxia with neuropathy and vestibular areflexia syndrome.

X-linked adrenoleukodystrophy presenting with positional downbeat nystagmus

A 20-year-old man presented with dizziness and gait disturbance for approximately 2 months. Neurologic examination revealed spontaneous downbeat nystagmus (DBN), limb ataxia, and abnormal tandem gait (video on the Neurology ® Web site at [Neurology.org][1]). Video-oculography showed augmented DBN during position change (figure 1). MRI revealed diffuse atrophy and signal changes in the brainstem and cerebellum (figure 2). The plasma levels of very long-chain fatty acids (C26:0 concentration, C24:0/C22:0 ratio, and C26:0/C22:0 ratio) were elevated. Subsequent genetic testing revealed a missense mutation in the ABCD1 gene. The olivopontocerebellar form of X-linked adrenoleukodystrophy should be considered a rare but possible diagnosis in young men with dizziness and DBN.1,2 Acknowledgment: All the clinical information and materials used in the present study were permitted for scientific use with written informed consent. This study was approved by the institutional review board of Chonnam National University Hospital. [1]: http://neurology.org/lookup/doi/10.1212/WNL.0000000000002749

Clinical Characteristics of Spontaneous Downbeat Nystagmus in Koreans: Analysis of 218 Cases

Background: Downbeat nystagmus is the most-common type of central nystagmus. However, no published study has attempted to analyze the etiology and clinical features of downbeat nystagmus in a large sample of Korean patients. Methods: We analyzed the demographic and clinical features of spontaneou s downbeat nystagmus in 218 Korean patients who had been evaluated at the Dizziness Clinic of Seoul National University Bundang Hospital from 2003 to 2014. Results: All patients were aged from 15 to 92 years (mean±SD: 58.7±18.0 years), and they included 117 (53.7%) men. Underlying causes were found in 162 patients (74.3%, secondary group), while no etiology was identified in the remaining patients (idiopathic group). The age and sex distributions did not differ between the idiopathic and secondary groups. The underlying etiology included hereditary disorders (n＝48, 22.0%), vascular diseases (n＝46, 21.1%), and inflammatory diseases (n＝19, 8.7%). Infarctions (n＝34, 15.6%) and episodic ataxia (n＝32, 14.7%) were the most-frequent underlying disorders. The most-common site of lesions identified by MRI was the cerebellum (68.9%), followed by the brainstem (28.6%). Among the 74 patients with lesions confirmed by MRI, 25 (33.7%) showed an isolated cerebellar involvement, while 35 (47.6%) had lesions in multiple areas. Conclusions: This study extends the clinical features of spontaneous downbeat nystagmus to Korean patients. Cerebellum is the most-common lesion site, which is consistent with the results of previous studies. The prevalence of Arnold-Chiari malformation is relatively low, which may be a di stinct finding relative to those of previous studies involving other ethnic populations. J Korean Neurol Assoc 34(1):27-32, 2016

Spontaneous downbeat nystagmus as a clue for the diagnosis of ataxia associated with anti-GAD antibodies

Glutamic acid decarboxylase (GAD) is the enzyme that catalyzes the conversion of glutamic acid to the neurotransmitter gamma-amino butyric acid. Antibodies against GAD (anti-GAD-Ab) are associated with an array of autoimmune-related neurological conditions, such as stiff-person syndrome, cerebellar ataxia, epilepsy and limbic encephalitis. The clinical spectrum of ataxia associated with anti-GAD-Ab comprises slowly progressive cerebellar ataxia syndrome evolving in months or years, associated with cerebellar atrophy on brain MRI. There are few reports of patients with ataxia associated with anti-GAD-Ab presenting with abnormal ocular movements, such as downbeat nystagmus (DBN). We present two patients with ataxia associated with anti-GAD-Ab from a large series of ataxic subjects who presented with cerebellar ataxia combined with spontaneous DBN. All patients underwent a thorough neurological evaluation with the use of ataxia scales, brain MRI scans, cerebrospinal fluid examination, 18FDG-PET/CT scans, laboratory work-up with onconeural and immune encephalitis antibodies, serum and cerebrospinal fluid levels of anti-GAD-Ab, and the antibody specificity index to measure the intrathecal synthesis of anti-GAD-Ab. All patients were treated with cycles of intravenous immunoglobulin and had mild/partial ataxia improvement and no improvement of DBN. The finding of DBN may work as a diagnostic clue in the context of adult-onset non-hereditary ataxias.

EHMTI-0320. Orthostatic headache and audiovestibular dysfunction associated with intracranial hypotension

Results Out of the 16 patients with intracranial hypotension, five (31%) had neuro-otological symptoms along with the orthostatic headache. One of them presented with recurrent spontaneous vertigo and tinnitus mimicking meniere’s disease (MD). Oculographic analysis documented abnormal eye movements in 38%, which include spontaneous downbeat nystagmus with variable positional modulation (n = 3, 19%) and positional upbeat nystagmus (n = 3, 19%). During the attack of vertigo in the patient with MD-like symptoms, we observed unidirectional horizontal and torsional nystagmus with normal head impulse test. Bithermal caloric tests were normal in all patients who tested. Audiometry showed unilateral or bilateral sensorineural hearing loss in about half of the patients. Conclusions Our study demonstrates that intracranial hypotension can induce higher frequency of audiovestibular dysfunction, which may be attributed to both irritation or dysfunction of the peripheral labyrinth or vestibulocochlear nerve, and brainstem or cerebellar dysfunction due to brain sagging. No conflict of interest.

Paraneoplastic downbeat nystagmus associated with cerebellar hypermetabolism especially in the nodulus

A 52-year-old man with vertigo and imbalance for two weeks showed spontaneous downbeat (DBN), horizontal gaze-evoked, and positional apogeotropic nystagmus along with severe limb and truncal ataxia. Gadolinium-enhanced brain MRI was normal, but whole body and brain 2-deoxy-2-[F18]fluoro-d-glucose-positron emission tomography revealed hypermetabolism in the right lower lobe of the lung and the cerebellum, especially in the nodulus. The lesion in the lung was confirmed as mixed cell carcinoma. Paraneoplastic DBN may be associated with cerebellar hypermetabolism, especially in the nodulus.

Downbeat nystagmus as the initial manifestation of anti-NMDAR encephalitis

Downbeat nystagmus (DBN) is a rare neurological disorder characterized by slow upward drifts and fast downward phases [1]. In most cases no anatomical lesion is identified, whereas Arnold-Chiari malformation or spinocerebellar degeneration may underlie this condition [1]. AntiNMDAR (N-methyl-D-aspartate receptor) encephalitis rarely causes DBN [2]. Recently, we observed a young lady showing DBN as the sole initial manifestation. A 21-year-old lady presented with the 5-day history of dizziness that worsened gradually. On examination she had spontaneous DBN, which was occasionally overlapped with ocular flutter-like movement. Smooth pursuit was slightly saccadic, and during horizontal gaze horizontal nystagmus overlapped DBN. Eye movements were otherwise intact. She had no intentional tremor or dysmetria on finger-to-nose and heel-to-shin testing. However, her gait was wide-based and mildly unsteady. The remainder of her examination was normal. However, 4 days later, emotional lability and delirium manifested, gradually followed by involuntary movement (crawl swimming-like, myoclonic), mutism, and hyperpnea/apnea that eventually required mechanical ventilation (Fig. 1). Brain magnetic resonance imaging (MRI) on the admission day showed normal findings throughout the course of disease. Single-photon emission computed tomography (SPECT) on the third day showed decrease cerebral perfusion in the medial frontal cortex. An electroencephalography (EEG) was normal. Routine blood studies showed no abnormalities. Cerebrospinal fluid (CSF) analysis showed mildly increased cell count of 35/mm (mononuclear:polymorphonuclear = 32:3) and normal total protein. Viral antigens were all negative. Although survey for malignancies including ovary and paraneoplastic antibodies including anti-Hu, anti-Yo and anti-GAD was negative, she was suspected to have autoimmune encephalitis. Steroid pulse and high-dose intravenous immunoglobulin (IVIG) therapy was of limited benefit. However, anti-NMDAR antibodies in CSF appeared to be increased significantly. From the 37th day she underwent plasmapheresis, which ameliorated significantly her involuntary movement and mildly her level of consciousness. Repeated CT scans of the pelvis showed a 1.5 cm ovarian mass. On the 69th day she underwent tumor resection, which revealed a 14 mm * 13 mm mature teratoma. This surgery brought her to normal consciousness. Previously, DBN has been seldom reported in paraneoplastic encephalitis except for anti-Ma2 antibody encephalitis (one case) [3], anti-glutamate acid decarboxilase (GAD) antibody encephalitis (one case) [4], and anti-NMDAR encephalitis (one case) with upbeat nystagmus at the plateau stage under mechanical ventilation [2]. Our patient was unique in that she presented with DBN and dizziness as the sole initial manifestation. Experimental and functional neuroimaging studies indicated that DBN is caused by dysfunction of the vestibulocerebellum (flocculus, nodulus of cerebellar vermis) and, rarely, bilateral paramedian brainstem [1]. Although brainstem and cerebellum are not commonly Y. Tsuyusaki R. Sakakibara (&) M. Kishi F. Tateno Neurology, Internal Medicine, Sakura Medical Center, Toho University, 564-1 Shimoshizu, Sakura 285-8741, Japan e-mail: sakakibara@sakura.med.toho-u.ac.jp

Ocular motor characteristics of different subtypes of spinocerebellar ataxia: Distinguishing features

Because of frequent involvement of the cerebellum and brainstem, ocular motor abnormalities are key features of spinocerebellar ataxias and may aid in differential diagnosis. Our objective for this study was to distinguish the subtypes by ophthalmologic features after head-shaking and positional maneuvers, which are not yet recognized as differential diagnostic tools in most common forms of spinocerebellar ataxias. Of the 302 patients with a diagnosis of cerebellar ataxia in 3 Korean University Hospitals from June 2011 to June 2012, 48 patients with spinocerebellar ataxia types 1, 2, 3, 6, 7, or 8 or with undetermined spinocerebellar ataxias were enrolled. All patients underwent a video-oculographic recording of fixation abnormalities, gaze-evoked nystagmus, positional and head-shaking nystagmus, and dysmetric saccades. Logistic regression analysis controlling for disease duration revealed that spontaneous and positional downbeat nystagmus and perverted head-shaking nystagmus were strong predictors for spinocerebellar ataxia 6, whereas saccadic intrusions and oscillations were identified as positive indicators of spinocerebellar ataxia 3. In contrast, the presence of gaze-evoked nystagmus and dysmetric saccades was a negative predictor of spinocerebellar ataxia 2. Positional maneuvers and horizontal head shaking occasionally induced or augmented saccadic intrusions/oscillations in patients with spinocerebellar ataxia types 1, 2, and 3 and undetermined spinocerebellar ataxia. The results indicated that perverted head-shaking nystagmus may be the most sensitive parameter for SCA6, whereas saccadic intrusions/oscillations are the most sensitive for spinocerebellar ataxia 3. In contrast, a paucity of gaze-evoked nystagmus and dysmetric saccades is more indicative of spinocerebellar ataxia 2. Head-shaking and positional maneuvers aid in defining ocular motor characteristics in spinocerebellar ataxias. © 2013 Movement Disorder Society.

The ataxic mouse as a model for studying downbeat nystagmus

Downbeat nystagmus (DBN) is a common eye movement complication of cerebellar disease. Use of mice to study pathophysiology of vestibulocerebellar disease is increasing, but it is unclear if mice can be used to study DBN; it has not been reported in this species. We determined whether DBN occurs in the ataxic mutant tottering, which carries a mutation in the Cacna1a gene for P/Q calcium channels. Spontaneous DBN occurred only rarely, and its magnitude did not exhibit the relationship to head tilt seen in human patients. DBN during yaw rotation was more common and shares some properties with the tilt-independent, gaze-independent component of human DBN, but differs in its dependence on vision. Hyperactivity of otolith circuits responding to pitch tilts is hypothesized to contribute to the gaze-independent component of human DBN. Mutants exhibited hyperactivity of the tilt maculo-ocular reflex (tiltMOR) in pitch. The hyperactivity may serve as a surrogate for DBN in mouse studies. TiltMOR hyperactivity correlates with hyperdeviation of the eyes and upward deviation of the head during ambulation; these may be alternative surrogates. Muscimol inactivation of the cerebellar flocculus suggests a floccular role in the tiltMOR hyperactivity and provides insight into the rarity of frank DBN in ataxic mice.

VGCC antibody-positive paraneoplastic cerebellar degeneration presenting with positioning vertigo

A 70-year-old woman developed paraneoplastic cerebellar degeneration (PCD) due to P/Q-type and N-type voltage-gated calcium channel antibodies and small cell lung cancer, the main clinical manifestations of which were severe positioning vertigo and vomiting. Loss of the visual suppression of caloric nystagmus, spontaneous downbeat nystagmus, periodic alternating nystagmus, and positioning vertigo in our patient most probably corresponds to the cerebellar flocculus/paraflocculus lesion caused by PCD.

Vertical nystagmus: clinical facts and hypotheses

The pathophysiology of spontaneous upbeat (UBN) and downbeat (DBN) nystagmus is reviewed in the light of several instructive clinical findings and experimental data. UBN due to pontine lesions could result from damage to the ventral tegmental tract (VTT), originating in the superior vestibular nucleus (SVN), coursing through the ventral pons and transmitting excitatory upward vestibular signals to the third nerve nucleus. A VTT lesion probably leads to relative hypoactivity of the drive to the motoneurons of the elevator muscles with, consequently, an imbalance between the downward and upward systems, resulting in a downward slow phase. The results observed in internuclear ophthalmoplegia suggest that the medial longitudinal fasciculus (MLF) is involved in the transmission of both upward and downward vestibular signals. Since no clinical cases of DBN due to focal brainstem damage have been reported, it may be assumed that the transmission of downward vestibular signals depends only upon the MLF, whereas that of upward vestibular signals involves both the MLF and the VTT. The main focal lesions resulting in DBN affect the cerebellar flocculus and/or paraflocculus. Apparently, this structure tonically inhibits the SVN and its excitatory efferent tract (i.e. the VTT) but not the downward vestibular system. Therefore, a floccular lesion could result in a disinhibition of the SVN-VTT pathway with, consequently, relative hyperactivity of the drive to the motoneurons of the elevator muscles, resulting in an upward slow phase. UBN also results from lesions affecting the caudal medulla. An area in this region could form part of a feedback loop involved in upward gaze-holding, originating in a collateral branch of the VTT and comprising the caudal medulla, the flocculus and the SVN, successively. Therefore, it is suggested that the main types of spontaneous vertical nystagmus due to focal central lesions result from a primary dysfunction of the SVN-VTT pathway, which becomes hypoactive after pontine or caudal medullary lesions, thereby eliciting UBN, and hyperactive after floccular lesions, thereby eliciting DBN. Lastly, since gravity influences UBN and DBN and may facilitate the downward vestibular system and restrain the upward vestibular system, it is hypothesized that the excitatory SVN-VTT pathway, along with its specific floccular inhibition, has developed to counteract the gravity pull. This anatomical hyperdevelopment is apparently associated with a physiological upward velocity bias, since the gain of all upward slow eye movements is greater than that of downward slow eye movements in normal human subjects and in monkeys.

Deficits in vertical and torsional eye movements after uni- and bilateral muscimol inactivation of the interstitial nucleus of Cajal of the alert monkey.

The mesencephalic interstitial nucleus of Cajal (iC) is considered the neural integrator for vertical and torsional eye movements and has also been proposed to be involved in saccade generation. The aim of this study was to elucidate the function of iC in neural integration of different types of eye movements and to distinguish eye movement deficits due to iC impairment from that of the immediately adjacent rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF). We addressed the following questions: (1) According to the neural integrator hypothesis, all eye movements including the saccadic system and the vestibulo-ocular reflex (VOR) share a common neural integrator. Do iC lesions impair gaze-holding function for vertical and torsional eye positions and the torsional and vertical VOR gain to a similar degree? (2) What are the dynamic properties of vertical and torsional eye movements deficits after iC lesions, e.g., the specificity of torsional and vertical nystagmus? (3) Is iC involved in saccade generation? We performed 13 uni- and three bilateral iC inactivations by muscimol microinjections in four alert monkeys. Three-dimensional eye movements were studied under head-stationary conditions during vertical and torsional VOR. Under static conditions, unilateral iC injections evoked a shift of Listing's plane to the contralesional side (up to 20 degrees), which increased (ipsilesional ear down) or decreased (ipsilesional ear up) by additional static vestibular stimulation in the roll plane, i.e., ocular counterroll was preserved. The monkeys showed a spontaneous torsional nystagmus with a profound downbeat component. The fast phases of torsional nystagmus always beat toward the lesion side (ipsilesional). Pronounced gaze-holding deficit for torsional and vertical eye positions (neural integrator failure) was reflected by the reduction of time constants of the exponential decay of the slow phase to 330-370 ms. Whereas the vertical oculomotor range was profoundly decreased (up to 50%) and vertical saccades were reduced in amplitude, saccade velocity remained normal and horizontal eye movements were not affected. Bilateral iC injections reduced the shift of Listing's plane caused by unilateral injections, i.e., back toward the plane of zero torsion. Torsional nystagmus reversed its direction and ceased, whereas vertical nystagmus persisted. In contrast to unilateral injection, there was additional upbeating nystagmus. Time constants of the position integrator of the gaze-holding system did not differ between unilateral and bilateral injections. The range of stable vertical eye positions and saccade amplitude was smaller when compared with unilateral injections, but the main sequence remained normal. Dynamic vestibular stimulation after unilateral iC injections had virtually no effect on torsional and vertical VOR gain and phase at the same time when time constants already indicated severe integrator failure. Torsional VOR elicited a constant slow-phase velocity offset up to 30 degrees toward the contralesional side, i.e., in the opposite direction to spontaneous torsional nystagmus. Likewise, vertical VOR showed a velocity offset in an upward direction, i.e., opposite to the spontaneous downbeat nystagmus. Contralesional torsional and upward vertical quick phases were missing or severely reduced in amplitude but showed normal velocity. In contrast, bilateral iC injections reduced the gain of the torsional and vertical VOR by 50% and caused a phase lead of 10-20 degrees (eye compared with head velocity). We propose that the slow-phase velocity offset during torsional and vertical VOR reflects a vestibular imbalance. It therefore appears likely that the vertical and torsional nystagmus after iC lesions is not only caused by a neural integrator failure but also by a vestibular imbalance. Unilateral iC injections have clearly differential effects on the VOR and the gaze-holding function. (ABSTRACT TRUNCATED)

A Case of AcquiredNystagmus AlternansAssociated with Acute Cerebellitis

A case of acquired nystagmus alternans (alternating nystagmus) is reported. The patient was a 14-year-old boy who presented with fever and headache, followed by dysbasia, truncal ataxia, and positional vertigo. Neuro-otological examinations revealed spontaneous downbeat nystagmus, bilateral gaze nystagmus and rebound nystagmus. Both cell count and protein volume were elevated in the cerebrospinal fluid, and a diagnosis of cerebellitis was made. About one month later, nystagmus alternans was observed, but it disappeared after 7 months. The presence of spontaneous downbeat nystagmus, rebound nystagmus, as well as cerebellar signs indicated that a cerebellar lesion was mainly responsible for the nystagmus alternans in this patient.

急性リチウム中毒の一症例

Tatsuo Funakubo, Tadashi Nakamura, Yo Kimura, Ryoji Kanayama, Makoto Ohki, Ryoichi Sano and Yoshio Koike (Yamagata University)A case of acute lithium intoxication is reported. The patient was a 34-year-old woman, administered lithium at a daily dose of 1000 mg for depression since 1981. On January 21,1990, she took 20 g of lithium to commit suiside and fell into a state of coma. She recovered and was admitted in our Department of Psychiatry.She showed low consciousness, lingual and mandibular involuntary movements, ataxic gait and dysarthria and was diagnosed as acute lithium intoxication. CT and MRI in dicated no abnormal findings in the brain.Neuro-otological examination w a s performed on February 19,1990. Spontaneous down-beat nystagmus was shown in the light. A gaze test showed gaze directional nystagmus horizontally and rebound nystagmus. An eye tracking test indicated saccadic pursuit on the horizontal axis and superimposed spontaneous nystagmus on the vertical axis. Slow phase OKN velocity was severely impaired bilaterally. A saccade test showed hypometric saccade, but velocity of which was normal.These findings suggested that the lesion in t h is case was not only in the cerebellum but also in the brainstem.