Effect of 3,4-diaminopyridine on the gravity dependence of ocular drift in downbeat nystagmus

Downbeat nystagmus: a clinical and pathophysiological review

Downbeat nystagmus (DBN) is a neuro-otological finding frequently encountered by clinicians dealing with patients with vertigo. Since DBN is a finding that should be understood because of central vestibular dysfunction, it is necessary to know how to frame it promptly to suggest the correct diagnostic-therapeutic pathway to the patient. As knowledge of its pathophysiology has progressed, the importance of this clinical sign has been increasingly understood. At the same time, clinical diagnostic knowledge has increased, and it has been recognized that this sign may occur sporadically or in association with others within defined clinical syndromes. Thus, in many cases, different therapeutic solutions have become possible. In our work, we have attempted to systematize current knowledge about the origin of this finding, the clinical presentation and current treatment options, to provide an overview that can be used at different levels, from the general practitioner to the specialist neurologist or neurotologist.

Nystagmus: Diagnosis, Topographic Anatomical Localization and Therapy

Nystagmus is defined as rhythmic, most often involuntary eye movements. It normally consists of a slow (pathological) drift of the eyes, followed by a fast central compensatory movement back to the primary position (refixation saccade). The direction, however, is reported according to the fast phase. The cardinal symptoms are, on the one hand, blurred vision, jumping images (oscillopsia), reduced visual acuity and, sometimes, double vision; many of these symptoms depend on the eye position. On the other hand, depending on the etiology, patients may suffer from the following symptoms: 1. permanent dizziness, postural imbalance, and gait disorder (typical of downbeat and upbeat nystagmus); 2. if the onset of symptoms is acute, the patient may experience spinning vertigo with a tendency to fall to one side (due to ischemia in the area of the brainstem or cerebellum with central fixation nystagmus or as acute unilateral vestibulopathy with spontaneous peripheral vestibular nystagmus); or 3. positional vertigo. There are two major categories: the first is spontaneous nystagmus, i.e., nystagmus which occurs in the primary position as upbeat or downbeat nystagmus; and the second includes various types of nystagmus which are induced or modified by certain factors. Examples are gaze-evoked nystagmus, head-shaking nystagmus, positional nystagmus, and hyperventilation-induced nystagmus. In addition, there are disorders similar to nystagmus, such as ocular flutter or opsoclonus. The most common central types of spontaneous nystagmus are downbeat and upbeat, infantile, pure torsional, pendular fixation, periodic alternating, and seesaw nystagmus. Many types of nystagmus allow a precise neuroanatomical localization: for instance, downbeat nystagmus, which is most often caused by a bilateral floccular lesion or dysfunction, or upbeat nystagmus, which is caused by a lesion in the midbrain or medulla. Examples of drug treatment are the use of 4-aminopyridine for downbeat and upbeat nystagmus, memantine or gabapentin for pendular fixation nystagmus, or baclofen for periodic alternating nystagmus. In this article we are focusing on nystagmus. In a second article we will focus on central ocular motor disorders, such as saccade or gaze palsy, internuclear ophthalmoplegia, and gaze-holding deficits. Therefore, these types of eye movements will not be described here in detail.

[Ocular movement and nystagmus: basics and clinical diagnosis]

BACKGROUND

Eye movements are one of the most complex motor functions of the central nervous system (CNS). Eye movement disorders including nystagmus occur in diseases of the CNS and the vestibular system. A systematic clinical examination often allows a topodiagnostic classification of the lesion.

OBJECTIVE

The basics of eye movements, the role of the cerebellum, the clinical examination of the oculomotor system, and the most important forms of nystagmus and their diagnostic implications are described.

MATERIALS AND METHODS

A literature analysis assessing eye movements, cerebellar control of eye movements, clinical examination of eye movement, and nystagmus was performed.

RESULTS

In disorders of eye movement, diseases of the oculomotor cranial nerves and the central nervous structures are to be distinguished from diseases of the orbit, eye muscles, and motor end plates. The former result in cranial nerve-related paralysis of extraocular muscles, disturbances of saccadic and smooth pursuit eye movements, vertical or horizontal gaze palsy, internuclear ophthalmoplegia, or impaired gaze holding. Nystagmus in combination with other disturbances of ocular movement is highly related to a lesion within the CNS. Intense nystagmus with a rotatory component that decreases during fixation usually has a peripheral vestibular cause.

CONCLUSION

Clinical examination of eye movements and nystagmus enables the diagnosis of typical eye movement disorders with a strong relation to distinct lesions of the CNS or the peripheral vestibular pathway.

Central positional nystagmus: Characteristics and model-based explanations

The central vestibular system operates to precisely estimate the rotational velocity and gravity orientation using the inherently ambiguous information from peripheral vestibular system. Therefore, any lesions disrupting this function can generate positional nystagmus. Central positional nystagmus (CPN) can be classified into the paroxysmal (transient) and persistent forms. The paroxysmal CPN has the features suggesting a semicircular canal origin regarding the latency, duration, and direction of nystagmus. Patients with paroxysmal CPN commonly show several different types of nystagmus classified according to the provoking positioning. The persistent form of CPN mostly appears as downbeat nystagmus while prone or supine, or apogeotropic or geotropic horizontal nystagmus when the head is turned to either side while supine. CPN may be ascribed to erroneous neural processing within the velocity-storage circuit that functions in estimating angular head velocity, gravity direction, and inertia. Paroxysmal CPN appears to be post-rotatory rebound nystagmus due to lesions involving the cerebellar nodulus and uvula. In contrast, persistent CPN may arise from erroneous gravity estimation. The overlap of lesion location responsible for both paroxysmal and persistent CPN may account for the frequent coexistence of both forms of nystagmus in a single patient.

Postural Ataxia in Cerebellar Downbeat Nystagmus: Its Relation to Visual, Proprioceptive and Vestibular Signals and Cerebellar Atrophy

Background

The cerebellum integrates proprioceptive, vestibular and visual signals for postural control. Cerebellar patients with downbeat nystagmus (DBN) complain of unsteadiness of stance and gait as well as blurred vision and oscillopsia.

Objectives

The aim of this study was to elucidate the differential role of visual input, gaze eccentricity, vestibular and proprioceptive input on the postural stability in a large cohort of cerebellar patients with DBN, in comparison to healthy age-matched control subjects.

Methods

Oculomotor (nystagmus, smooth pursuit eye movements) and postural (postural sway speed) parameters were recorded and related to each other and volumetric changes of the cerebellum (voxel-based morphometry, SPM).

Results

Twenty-seven patients showed larger postural instability in all experimental conditions. Postural sway increased with nystagmus in the eyes closed condition but not with the eyes open. Romberg’s ratio remained stable and was not different from healthy controls. Postural sway did not change with gaze position or graviceptive input. It increased with attenuated proprioceptive input and on tandem stance in both groups but Romberg’s ratio also did not differ. Cerebellar atrophy (vermal lobule VI, VIII) correlated with the severity of impaired smooth pursuit eye movements of DBN patients.

Conclusions

Postural ataxia of cerebellar patients with DBN cannot be explained by impaired visual feedback. Despite oscillopsia visual feedback control on cerebellar postural control seems to be preserved as postural sway was strongest on visual deprivation. The increase in postural ataxia is neither related to modulations of single components characterizing nystagmus nor to deprivation of single sensory (visual, proprioceptive) inputs usually stabilizing stance. Re-weighting of multisensory signals and/or inappropriate cerebellar motor commands might account for this postural ataxia.

A randomised double-blind, cross-over trial of 4-aminopyridine for downbeat nystagmus--effects on slowphase eye velocity, postural stability, locomotion and symptoms

OBJECTIVE

The effects of 4-aminopyridine (4-AP) on downbeat nystagmus (DBN) were analysed in terms of slow-phase velocity (SPV), stance, locomotion, visual acuity (VA), patient satisfaction and side effects using standardised questionnaires.

METHODS

Twenty-seven patients with DBN received 5 mg 4-AP four times a day or placebo for 3 days and 10 mg 4-AP four times a day or placebo for 4 days. Recordings were done before the first, 60 min after the first and 60 min after the last drug administration.

RESULTS

SPV decreased from 2.42 deg/s at baseline to 1.38 deg/s with 5 mg 4-AP and to 2.03 deg/s with 10 mg 4-AP (p<0.05; post hoc: 5 mg 4-AP: p=0.04). The rate of responders was 57%. Increasing age correlated with a 4-AP-related decrease in SPV (p<0.05). Patients improved in the 'get-up-and-go test' with 4-AP (p<0.001; post hoc: 5 mg: p=0.025; 10 mg: p<0.001). Tandem-walk time (both p<0.01) and tandem-walk error (4-AP: p=0.054; placebo: p=0.059) improved under 4-AP and placebo. Posturography showed that some patients improved with the 5 mg 4-AP dose, particularly older patients. Near VA increased from 0.59 at baseline to 0.66 with 5 mg 4-AP (p<0.05). Patients with idiopathic DBN had the greatest benefit from 4-AP. There were no differences between 4-AP and placebo regarding patient satisfaction and side effects.

CONCLUSIONS

4-AP reduced SPV of DBN, improved near VA and some locomotor parameters. 4-AP is a useful medication for DBN syndrome, older patients in particular benefit from the effects of 5 mg 4-AP on nystagmus and postural stability.

Comparison of 10-mg doses of 4-aminopyridine and 3,4-diaminopyridine for the treatment of downbeat nystagmus

OBJECTIVE

Animal experiments have demonstrated that aminopyridines increase Purkinje cell excitability, and in clinical studies, 4-aminopyridine (4-AP) and 3,4-diaminopyridine (3,4-DAP) improved downbeat nystagmus. In this double-blind, prospective, crossover study, the effects of equivalent doses of 4-AP and 3,4-DAP on the slow-phase velocity (SPV) of downbeat nystagmus were compared.

METHODS

Eight patients with downbeat nystagmus due to different etiologies (cerebellar degeneration [n = 1], bilateral vestibulopathy [n = 1], bilateral vestibulopathy and cerebellar degeneration [n = 1], Arnold-Chiari I malformation and cerebellar ataxia [n = 1], cryptogenic cerebellar ataxia [n = 4]) were included. They were randomly assigned to receiving a single capsule of 10 mg of 3,4-DAP or 4-AP followed by 6 days with no medication. One week later, the treatment was switched, that is, 1 single capsule (10 mg) of the other agent. Recordings with 3-dimensional video-oculography were performed before and 45 and 90 minutes after drug administration.

RESULTS

Both medications had a significant effect throughout time (pre vs post 45 vs post 90) (F() = 8.876; P < 0.01). Following the administration of 3,4-DAP, mean slow velocity decreased from -5.68°/s (pre) to -3.29°/s (post 45) to -2.96°/s (post 90) (pre vs post 45/post 90 P < 0.01). In 4-AP, the mean SPV decreased from -6.04°/s (pre) to -1.58°/s (post 45) to -1.21°/s (post 90) (pre vs post 45/post 90 P < 0.00001). Both after 45 and after 90, the mean SPVs were significantly lower for 4-AP than for 3,4-DAP (P < 0.05). None of the patients reported serious side effects.

CONCLUSION

Based on these results, 10-mg doses of 4-AP lead to a more pronounced decrease of the SPV of downbeat nystagmus than do equivalent doses of 3,4-DAP.

Paraneoplastic disorders of eye movements

Paraneoplastic syndromes affecting the brainstem and cerebellum are reported to cause a variety of abnormalities of eye movements. Recent studies have begun to account for the mechanisms underlying several syndromes, characterized by opsoclonus, slow, or dysmetric saccades, as well as downbeat nystagmus. We provide evidence that upbeat nystagmus in a female patient with pancreatic cancer reflected a cerebellar-induced imbalance of otolithic pathways: she showed marked retropulsion, and her nystagmus was dependent on head position, being absent when supine, and suppressed with convergence. In addition to anti-Hu antibodies, we demonstrated antibodies to a novel neuronal cell surface antigen. Taken with other recent studies, our findings suggest that paraneoplastic syndromes arise due to antibodies against surface neuronal antigens, including receptors and channels. Abnormal eye movements in paraneoplastic syndromes offer insights into the pathogenesis of these disorders and the opportunity to test potential therapies, such as new drugs with effects on neuronal channels.

Therapy for nystagmus

Pathological forms of nystagmus and their visual consequences can be treated using pharmacological, optical, and surgical approaches. Acquired periodic alternating nystagmus improves following treatment with baclofen, and downbeat nystagmus may improve following treatment with aminopyridines. Gabapentin and memantine are helpful in reducing acquired pendular nystagmus due to multiple sclerosis. Ocular oscillations in oculopalatal tremor may also improve following treatment with memantine or gabapentin. The infantile nystagmus syndrome (INS) may have only a minor impact on vision if "foveation periods" are well developed, but symptomatic patients may benefit from treatment with gabapentin, memantine, or base-out prisms to induce convergence. Several surgical therapies are also reported to improve INS, but selection of the optimal treatment depends on careful evaluation of visual acuity and nystagmus intensity in various gaze positions. Electro-optical devices are a promising and novel approach for treating the visual consequences of acquired forms of nystagmus.

Current treatment of vestibular, ocular motor disorders and nystagmus

Vertigo and dizziness are among the most common complaints with a lifetime prevalence of about 30%. The various forms of vestibular disorders can be treated with pharmacological therapy, physical therapy, psychotherapeutic measures or, rarely, surgery. In this review, the current pharmacological treatment options for peripheral and central vestibular, cerebellar and ocular motor disorders will be described. They are as follows for peripheral vestibular disorders. In vestibular neuritis recovery of the peripheral vestibular function can be improved by treatment with oral corticosteroids. In Menière's disease a recent study showed long-term high-dose treatment with betahistine has a significant effect on the frequency of the attacks. The use of aminopyridines introduced a new therapeutic principle in the treatment of downbeat and upbeat nystagmus and episodic ataxia type 2 (EA 2). These potassium channel blockers presumably increase the activity and excitability of cerebellar Purkinje cells, thereby augmenting the inhibitory influence of these cells on vestibular and cerebellar nuclei. A few studies showed that baclofen improves periodic alternating nystagmus, and gabapentin and memantine, pendular nystagmus. However, many other eye movement disorders such as ocular flutter opsoclonus, central positioning, or see-saw nystagmus are still difficult to treat. Although progress has been made in the treatment of vestibular neuritis, downbeat and upbeat nystagmus, as well as EA 2, state-of-the-art trials must still be performed on many vestibular and ocular motor disorders, namely Menière's disease, bilateral vestibular failure, vestibular paroxysmia, vestibular migraine, and many forms of central eye movement disorders.

Pharmacotherapy of vestibular and ocular motor disorders, including nystagmus

We review current pharmacological treatments for peripheral and central vestibular disorders, and ocular motor disorders that impair vision, especially pathological nystagmus. The prerequisites for successful pharmacotherapy of vertigo, dizziness, and abnormal eye movements are the "4 D's": correct diagnosis, correct drug, appropriate dosage, and sufficient duration. There are seven groups of drugs (the "7 A's") that can be used: antiemetics; anti-inflammatory, anti-Ménière's, and anti-migrainous medications; anti-depressants, anti-convulsants, and aminopyridines. A recovery from acute vestibular neuritis can be promoted by treatment with oral corticosteroids. Betahistine may reduce the frequency of attacks of Ménière's disease. The aminopyridines constitute a novel treatment approach for downbeat and upbeat nystagmus, as well as episodic ataxia type 2 (EA 2); these drugs may restore normal "pacemaker" activity to the Purkinje cells that govern vestibular and cerebellar nuclei. A limited number of trials indicate that baclofen improves periodic alternating nystagmus, and that gabapentin and memantine improve acquired pendular and infantile (congenital) nystagmus. Preliminary reports suggest suppression of square-wave saccadic intrusions by memantine, and ocular flutter by beta-blockers. Thus, although progress has been made in the treatment of vestibular neuritis, some forms of pathological nystagmus, and EA 2, controlled, masked trials are still needed to evaluate treatments for many vestibular and ocular motor disorders, including betahistine for Ménière's disease, oxcarbazepine for vestibular paroxysmia, or metoprolol for vestibular migraine.

Central oculomotor disturbances and nystagmus: a window into the brainstem and cerebellum

BACKGROUND

Oculomotor disturbances and nystagmus are seen in many diseases of the nervous system, the vestibular apparatus, and the eyes, as well as in toxic and metabolic disorders. They often indicate a specific underlying cause. The key to diagnosis is systematic clinical examination of the patient's eye movements. This review deals mainly with central oculomotor disturbances, i.e., those involving smooth pursuit, saccades, gaze-holding, and central types of nystagmus.

METHODS

We searched the current literature for relevant publications on the diagnosis and treatment of oculomotor disturbances and nystagmus, and discuss them selectively in this review along with the German Neurological Society's guidelines on the topic.

RESULTS

A detailed knowledge of the anatomy and physiology of eye movements usually enables the physician to localize the disturbance to a specific area in the brainstem or cerebellum. The examination of eye movements is an even more sensitive method than magnetic resonance imaging for the diagnosis of acute vestibular syndromes and for the differentiation of peripheral from central lesions. For example, isolated dysfunction of horizontal saccades is due to a pontine lesion, while isolated dysfunction of vertical saccades is due to a midbrain lesion. Generalized gaze-evoked nystagmus (GEN) has multiple causes; purely vertical GEN is due to a midbrain lesion, while purely horizontal GEN is due to a pontomedullary lesion. Internuclear ophthalmoplegia involves a constellation of findings, the most prominent of which is impaired adduction to the side of the causative lesion in the ipsilateral medial longitudinal fasciculus. The most common pathological types of central nystagmus are downbeat and upbeat nystagmus (DBN, UBN). DBN is generally due to cerebellar dysfunction, e.g., because of a neurodegenerative disease.

CONCLUSION

This short review focuses on the clinical characteristics, pathophysiology and current treatment of oculomotor disorders and nystagmus.

Treatments for neuro-ophthalmologic conditions

Neuro-ophthalmology covers disorders that fall between the cracks of Neurology and Ophthalmology. Neurologists see patients with neuro-ophthalmic disorders. Recognition of the diagnosis is difficult enough, but treatment can be challenging. This article reviews several common neuro-ophthalmic disorders, outlining their features and treatments, from retinal vascular disorders to eye movements and blepharospasm.

Nystagmus and saccadic intrusions

We review current concepts of nystagmus and saccadic oscillations, applying a pathophysiological approach. We begin by discussing how nystagmus may arise when the mechanisms that normally hold gaze steady are impaired. We then describe the clinical and laboratory evaluation of patients with ocular oscillations. Next, we systematically review the features of nystagmus arising from peripheral and central vestibular disorders, nystagmus due to an abnormal gaze-holding mechanism (neural integrator), and nystagmus occurring when vision is compromised. We then discuss forms of nystagmus for which the pathogenesis is not well understood, including acquired pendular nystagmus and congenital forms of nystagmus. We then summarize the spectrum of saccadic disorders that disrupt steady gaze, from intrusions to flutter and opsoclonus. Finally, we review current treatment options for nystagmus and saccadic oscillations, including drugs, surgery, and optical methods. Examples of each type of nystagmus are provided in the form of figures.

New methods for diagnosis and treatment of vestibular diseases

Dizziness and vertigo are common complaints, with a lifetime prevalence of over 30%. This review provides a brief summary of the recent diagnostic and therapeutic advances in the field of neuro-otology. A special focus is placed on the clinical usefulness of vestibular tests. While these have markedly improved over the years, treatment options for vestibular disorders still remain limited. Available therapies for selected vestibular diseases are discussed.

Medical treatment of vestibular disorders

BACKGROUND

The lifelong prevalence of rotatory vertigo is 30%. Despite this high figure, patients with vertigo generally receive either inappropriate or inadequate treatment. However, the majority of vestibular disorders have a benign cause, take a favorable natural course, and respond positively to therapy.

OBJECTIVE

This review puts special emphasis on the medical rather than the physical, operative, or psychotherapeutic treatments available.

METHODS

A selected review of recent reports and studies on the medical treatment of peripheral and central vestibular disorders.

RESULTS/CONCLUSIONS

In vestibular neuritis, recovery of the peripheral vestibular function can be improved by oral corticosteroids; in Menière's disease, there is first evidence that high-dose, long-term administration of betahistine reduces attack frequency; carbamazepine or oxcarbamazepine is the treatment of first choice in vestibular paroxysmia, a disorder mainly caused by neurovascular cross-compression; the potassium channel blocker aminopyridine provides a new therapeutic principle for treatment of downbeat nystagmus, upbeat nystagmus, and episodic ataxia type 2.

The intensity of downbeat nystagmus during daytime

On the basis of reports by patients with downbeat nystagmus (DBN) that their symptoms were worse during the morning but better during the daytime, we investigated whether the intensity of DBN changes during the daytime. DBN was measured at 9 am, 11 am, and 1 pm. The mean peak slow phase velocity (MPSPV) of DBN was determined in different eye positions, with and without fixation, as well as in three different body positions: sitting upright, lying supine with the nose up, and lying prone with the nose down. Twelve patients with DBN either due to cerebellar degeneration or of idiopathic etiology were examined. The major findings of this study were as follows. First, the intensity of DBN significantly decreased during the daytime. When measured in the sitting upright position and primary eye position, MPSPV decreased from 4.32 deg/sec (+/-SEM 1.02) at 9 am to 2.12 deg/sec (+/- 0.5) at 11 am (P < 0.01) and stayed constant around 1.93 deg/sec (+/- 0.57) at 1 pm (P < 0.01 from 9 am to 1 pm) and 2.08 deg/sec (+/- 0.75) at 3 pm (P < 0.01 from 9 am to 3 pm). Second, this change did not depend on fixation during the measurements. Third, this effect was not influenced by the eye position during the measurements (upward, downward, or straight ahead). Our data show that the intensity of DBN decreases during the daytime. This decrease correlates with the symptoms of the patients. This change during daytime did not depend on visual fixation. Another possible mechanism is the modulation of DBN by head position relative to gravity, that is, by otolith input. This should be evaluated in further studies.

[Pharmacotherapy of central oculomotor disorders]

Nystagmus causes blurred vision due to oscillopsia, as well as impaired balance. Depending on etiology, additional cerebellar and brain stem signs may occur. We present the current pharmacotherapy of the most common forms of central nystagmus: downbeat nystagmus (DBN), upbeat nystagmus (UBN), acquired pendular nystagmus (APN), and congenital nystagmus (CGN). Recommended medical therapies are aminopyridines (4-AP) for DBN and UBN, gabapentin and memantine for CGN and APN, and baclofen for periodic alternating nystagmus (PAN).

A model-based theory on the origin of downbeat nystagmus

The pathomechanism of downbeat nystagmus (DBN), an ocular motor sign typical for vestibulo-cerebellar lesions, remains unclear. Previous hypotheses conjectured various deficits such as an imbalance of central vertical vestibular or smooth pursuit pathways to be causative for the generation of spontaneous upward drift. However, none of the previous theories explains the full range of ocular motor deficits associated with DBN, i.e., impaired vertical smooth pursuit (SP), gaze evoked nystagmus, and gravity dependence of the upward drift. We propose a new hypothesis, which explains the ocular motor signs of DBN by damage of the inhibitory vertical gaze-velocity sensitive Purkinje cells (PCs) in the cerebellar flocculus (FL). These PCs show spontaneous activity and a physiological asymmetry in that most of them exhibit downward on-directions. Accordingly, a loss of vertical floccular PCs will lead to disinhibition of their brainstem target neurons and, consequently, to spontaneous upward drift, i.e., DBN. Since the FL is involved in generation and control of SP and gaze holding, a single lesion, e.g., damage to vertical floccular PCs, may also explain the associated ocular motor deficits. To test our hypothesis, we developed a computational model of vertical eye movements based on known ocular motor anatomy and physiology, which illustrates how cortical, cerebellar, and brainstem regions interact to generate the range of vertical eye movements seen in healthy subjects. Model simulation of the effect of extensive loss of floccular PCs resulted in ocular motor features typically associated with cerebellar DBN: (1) spontaneous upward drift due to decreased spontaneous PC activity, (2) gaze evoked nystagmus corresponding to failure of the cerebellar loop supporting neural integrator function, (3) asymmetric vertical SP deficit due to low gain and asymmetric attenuation of PC firing, and (4) gravity-dependence of DBN caused by an interaction of otolith-ocular pathways with impaired neural integrator function.

Oscillopsies : approches physiopathologique et thérapeutique

Oscillopsia is an illusion of an unstable visual world. It is associated with poor visual acuity and is a disabling and stressful symptom reported by numerous patients with neurological disorders. The goal of this paper is to review the physiology of the systems subserving stable vision, the various pathophysiological mechanisms of oscillopsia and the different treatments available. Visual stability is conditioned by two factors. First, images of the seen world projected onto the retina have to be stable, a sine qua non condition for foveal discriminative function. Vestibulo-ocular and optokinetic reflexes act to stabilize the retinal images during head displacements; ocular fixation tends to limit the occurrence of micro ocular movements during gazing; a specific system also acts to maintain the eyes stable during eccentric gaze. Second, although we voluntary move our gaze (body, head and eye displacements), the visual world is normally perceived as stable, a phenomenon known as space constancy. Indeed, complex cognitive processes compensate for the two sensory consequences of gaze displacement, namely an oppositely-directed retinal drift and a change in the relationship between retinal and spatial (or subject-centered) coordinates of the visual scene. In patients, oscillopsia most often results from abnormal eye movements which cause excessive motion of images on the retina, such as nystagmus or saccadic intrusions or from an impaired vestibulo-ocular reflex. Understanding the exact mechanisms of impaired eye stability may lead to the different treatment options that have been documented in recent years. Oscillopsia could also result from an impairment of spatial constancy mechanisms that in normal condition compensate for gaze displacements, but clinical data in this case are scarce. However, we suggest that some visuo-perceptive deficits consecutive to temporo-parietal lesions resemble oscillopsia and could result from a deficit in elaborating spatial constancy.

Pharmacological advances in the treatment of neuro-otological and eye movement disorders

PURPOSE OF REVIEW

First, to describe the current pharmacological treatment options for peripheral and central vestibular, cerebellar, and ocular motor disorders. Second, to identify vestibular and ocular motor disorders in which treatment trials are warranted.

RECENT FINDINGS

Peripheral vestibular disorders: In vestibular neuritis recovery of the peripheral vestibular function can be improved by treatment with oral corticosteroids. In Ménière's disease treatment strategies range from low-salt diet, diuretics, and betahistine, to intratympanic injection of corticosteroids or gentamicin. Unfortunately most of the trials on Ménière's disease do not have an up-to-date design. In bilateral vestibulopathy steroids do not seem to improve vestibular function.Central vestibular, cerebellar, and ocular motor disorders: The use of aminopyridines introduced a new therapeutic principle in the treatment of downbeat and upbeat nystagmus and episodic ataxia type 2 (EA2). These potassium channel blockers presumably increase the activity and excitability of cerebellar Purkinje cells, thereby augmenting the inhibitory influence of these cells on vestibular and cerebellar nuclei. A few studies showed that baclofen improves periodic alternating nystagmus, and gabapentin and memantine, pendular nystagmus. Many other eye movement disorders, however, such as ocular flutter, opsoclonus, central positioning, or see-saw nystagmus are still difficult to treat.

SUMMARY

Although progress has been made in the treatment of vestibular neuritis, downbeat and upbeat nystagmus, as well as EA2, state-of-the-art trials must still be performed on many vestibular and ocular motor disorders, namely Ménière's disease, bilateral vestibulopathy, vestibular paroxysmia, vestibular migraine, and many forms of central eye movement disorders.

Effect of 3,4-Diaminopyridine on the Postural Control in Patients with Downbeat Nystagmus

Downbeat nystagmus (DBN) is a common, usually persistent ocular motor sign in vestibulocerebellar midline lesions. Postural imbalance in DBN may increase on lateral gaze when downbeat nystagmus increases. 3,4-Diaminopyridine (3,4-DAP) has been shown to suppress the slow-phase velocity component of downbeat nystagmus and its gravity-dependent component with concomitant improvement of oscillopsia. Because the pharmacological effect is thought to be caused by improvement of the vestibulocerebellar Purkinje cell activity, the effect of 3,4-DAP on the postural control of patients with downbeat nystagmus syndrome was examined. Eye movements were recorded with the video-based Eyelink II system. Postural sway and pathway were assessed by posturography in lateral gaze in the light and on eye closure. Two out of four patients showed an improvement of the area of postural sway by 57% of control (baseline) on eye closure. In contrast, downbeat nystagmus in gaze straight ahead and on lateral gaze did not benefit in these two patients, implying a specific influence of 3,4-DAP on the vestibulocerebellar control of posture. It was concluded that 3,4-DAP may particularly influence the postural performance in patients with downbeat nystagmus.

Nystagmus: an update on treatment in adults

Recent developments in the treatment of nystagmus in adults have changed the traditional approach to such illnesses as benign paroxysmal positional vertigo, vestibular neuritis, Meniere's disease, superior canal dehiscence syndrome, vestibular paroxysmia, superior oblique myokymia, downbeat/upbeat nystagmus and acquired pendular nystagmus, as well as periodic alternating nystagmus. Treatments reported to suppress nystagmus, with tolerable side effects, are now available for some of these syndromes. Due to the absence of large controlled studies, however, treatment recommendations rest only on class C evidence.

Pharmacology of vertigo/nystagmus/oscillopsia

PURPOSE OF REVIEW

To describe recent developments in the pharmacological treatment of vertigo and nystagmus while focusing on vestibular neuritis, Meniere's disease, downbeat nystagmus, periodic alternating nystagmus, acquired pendular nystagmus, and superior oblique myokymia.

RECENT FINDINGS

In the last 2 years several studies have been published on possible pharmacological treatment options for nystagmus and oscillopsia. In the treatment of vestibular neuritis two studies showed that cortisone treatment was effective for restoring labyrinthine function. This benefit seems more likely if treatment is started within the first 2 days of onset. For recurrent vertigo attacks due to Meniere's disease, the titration technique with daily or weekly doses of intratympanic gentamicin until onset of vestibular symptoms, change in vertigo or hearing loss rated best for complete vertigo control. A new pharmacological treatment option for downbeat nystagmus is the administration of potassium channel blockers (e.g. 4-aminopyridine). They are thought to reinforce the inhibitory action of cerebellar Purkinje cells. Several case reports have proven the beneficial effect of baclofen on periodic alternating nystagmus, of gabapentin and memantine on acquired pendular nystagmus, and of carbamazepine and gabapentin on superior oblique myokymia.

SUMMARY

There have been several new developments in the treatment of nystagmus and vertigo over the last 2 years. These include potassium channel blockers for the treatment of downbeat nystagmus, early cortisone treatment to improve recovery of the labyrinth function in vestibular neuritis, and intratympanic gentamicin treatment for Meniere's disease. Other pharmacological treatment options are baclofen for periodic alternating nystagmus, gabapentin and memantine for acquired pendular nystagmus, and carbamazepine for superior oblique myokymia.