Downbeat nystagmus with a pseudocycloid waveform: improvement with base-out prisms

How should I approach and manage adult-onset oscillopsia?

Oscillopsia is the sensation of illusory movement within the visual percept leading to a degradation of visual functioning and quality of life. The constellation of conditions manifesting with oscillopsia marks the overlap between ophthalmology and otorhinolaryngology. The purpose of this article is therefore to review the aetiologies of oscillopsia and provide pathways for investigation and treatment of processes that associate oscillopsia with intrusive ocular movement and for processes manifesting as oscillopsia in the absence of intrusive ocular movement. Points for referral are also included for the diagnoses that are more appropriately investigated and managed by allied medical specialties.

Downbeat nystagmus: a clinical review of diagnosis and management

PURPOSE OF REVIEW

This review will extensively cover the clinical manifestations, causes, diagnostic evaluation, and management strategies of downbeat nystagmus (DBN).

RECENT FINDINGS

Historically, MRI to assess for structural lesions at the cervicomedullary junction has been the primary diagnostic test in the evaluation of DBN since the 1980s. In recent years, there is increasing awareness of nonstructural causes of DBN including gluten ataxia, nutritional deficiencies, and paraneoplastic syndromes, among others. Medical management with aminopyridines has become first-line therapy in addition to disease-specific therapies.

SUMMARY

DBN is a common form of acquired nystagmus and the differential diagnosis remains broad, including both benign and potentially fatal causes. For practical purposes, the causes can be categorized as structural vs. nonstructural with MRI as the ideal, initial diagnostic study to differentiate the two. General therapeutic options include pharmacotherapy to enhance Purkinje cell function, strabismus surgery or prisms to shift null points, and behavioural changes. Disease-specific treatment is necessarily broad, though a significant proportion of patients will be idiopathic.

Wernicke-Korsakoff Syndrome in Hyperemesis Gravidarum: A Case Report and Literature Review

BACKGROUND

Wernicke-Korsakoff syndrome (WKS) is a triad of ophthalmoplegia, ataxia and memory deficits due to thiamine insufficiency resulting from under- or untreated Wernicke's encephalopathy (WE), which may be associated with hyperemesis gravidarum (HEG).

CASE PRESENTATION

We present a case of a 36-year-old Filipino woman in her first trimester with HEG, along with the WKS triad and abnormal hyperintense signals in the bilateral thalami and midbrain, left occipital lobe, periaqueductal gray matter and pontine periventricular areas. Neurologic deficits partially improved but persisted despite intravenous thiamine administration.

EVIDENCE REVIEW

A review of current treatments for WE, and the prevention and neurocognitive recovery of WKS was done. The beneficial effects of thiamine for acute WKS are supported by several case reports and clinical experience. Evidence from one randomized controlled trial wherein thiamine was given in various doses for treating WE or preventing WKS in an alcohol-dependent population is limited by methodological issues. Rehabilitation and pharmacotherapy for neurocognitive recovery seems promising, but they have inadequate evidentiary support. More robust studies on multi-modal strategies are warranted to facilitate the neurocognitive recovery of patients with WKS.

Conversion of upbeat to downbeat nystagmus in Wernicke encephalopathy

OBJECTIVE

To explain (1) why an initial upbeat nystagmus (UBN) converts to a permanent downbeat nystagmus (DBN) in Wernicke encephalopathy (WE) and (2) why convergence and certain vestibular provocative maneuvers may transiently switch UBN to DBN.

METHODS

Following a literature review and study of our 2 patients, we develop hypotheses for the unusual patterns of vertical nystagmus in WE.

RESULTS

Our overarching hypothesis is that there is a selective vulnerability and a selective recovery from thiamine deficiency of neurons within brainstem gaze-holding networks. Furthermore, since the circuits affected in WE are commonly paraventricular, especially medially, just under the floor of the fourth ventricle where lie structures important for control of vertical gaze, we suggest the patterns of involvement in WE also reflect a breakdown in vulnerable areas of the blood-brain barrier. Many of the initial deficits of our patients improved over time, but their DBN did not. Irreversible changes in paramedian tract neurons, which project to the cerebellar flocculus, may be the cause. Here we suggest that conversion of UBN to permanent DBN points to thiamine deficiency and may argue for a chronic, nonprogressive DBN/truncal ataxia syndrome. Finally, we posit that the transient switch of UBN to DBN reflects abnormal processing of otolith information about linear acceleration, and often points to a diagnosis of WE.

CONCLUSION

Recognizing the unusual patterns of transient switching and then permanent conversion of UBN to DBN in WE is vital since long-term disability from WE may be prevented by timely, parenteral high-dose thiamine.

Symptomatic treatment and management of multiple sclerosis

The range of symptoms which occur in multiple sclerosis (MS) can have disabling functional consequences for patients and lead to significant reductions in their quality of life. MS symptoms can also interact with each other, making their management challenging. Clinical trials aimed at identifying symptomatic therapies have generally been poorly designed and have tended to be underpowered. Therefore, the evidence base for the management of MS symptoms with pharmacologic therapies is not strong and tends to rely upon open-label studies, case reports, and clinical trials with small numbers of patients and poorly validated clinical outcome measures. Recently, there has been a growing interest in the management of MS symptoms with pharmacologic treatments, and better-designed, randomized, double-blind, controlled trials have been reported. This chapter will describe the evidence base predominantly behind the various pharmacologic approaches to the management of MS symptoms, which in most, if not all, cases, requires multidisciplinary input. Drugs routinely recommended for individual symptoms and new therapies, which are currently in the development pipeline, will be reviewed. More interventional therapies related to symptoms that are refractory to pharmacotherapy will also be discussed, where relevant.

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.

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.

An update on acquired nystagmus

Proper evaluation and treatment of acquired nystagmus requires accurate characterization of nystagmus type and visual effects. This review addresses important historical and examination features of nystagmus and current concepts of pathogenesis and treatment of gaze-evoked nystagmus, nystagmus due to vision loss, acquired pendular nystagmus, peripheral and central vestibular nystagmus, and periodic alternating nystagmus.

Development of new treatments for congenital nystagmus

The use of ocular motor data as the basis for the development of both nonsurgical and surgical therapies for congenital nystagmus (CN) has been underway since the mid-1960s. This paper presents three nonsurgical therapies (composite prisms, soft contact lenses, and afferent stimulation) and a new surgical therapy (four-muscle tenotomy) hypothesized from analysis of ocular motor data. The expanded nystagmus acuity function test was developed to both predict and measure the effectiveness of CN therapies and for intersubject comparisons. Base-out prisms may be used to damp CN during distance fixation in patients whose CN damps during near fixation and who are binocular (i.e., they have no strabismus). Soft contact lenses may be used in those whose CN damps with afferent stimulation of the ophthalmic division of the trigeminal nerve. Cutaneous afferent stimulation (rubbing, vibration, or electricity) of the forehead or neck damps CN in some individuals. Finally, as first demonstrated in an achiasmic Belgian sheepdog and later in humans, tenotomy of the four horizontal rectus muscles and reattachment at their original sites may also damp CN. Taken together, these findings suggest the existence of one or more proprioceptive feedback loops acting to change the small-signal gain of the extraocular plant. Four-muscle tenotomy provides a needed therapeutic option for the many individuals with CN for whom other surgical therapies are contraindicated. Tenotomy may also prove useful in see-saw nystagmus (it abolished it in the aforementioned canine) or other types of nystagmus; further studies of the latter are required.

A new surgery for congenital nystagmus: effects of tenotomy on an achiasmatic canine and the role of extraocular proprioception

PURPOSE

Human eye-movement recordings have documented that surgical treatment of congenital nystagmus (CN) also produces a broadening of the null zone and changes in foveation that allow increased acuity. We used the achiasmatic Belgian sheepdog, a spontaneously occurring animal model of human CN and see-saw nystagmus (SSN), to test the hypothesis that changes induced by surgical interruption of the extraocular muscle afference without a change in muscle-length tension could damp both oscillations.

METHODS

An achiasmatic dog with CN and SSN underwent videotaping and infrared oculography in a sling apparatus and head restraints before and after all extraocular muscles (stage 1: 4 horizontal rectus muscles and stage 2 [4 months later]: 4 vertical rectus muscles and 4 oblique muscles) were surgically tenotomized and immediately reattached at their original insertions.

RESULTS

The dog had immediate and persistent visible, behavioral, and oculographic changes after each stage of this new procedure. These included damped CN and SSN, increased ability to maintain fixation, and increased periods of maintaining the target image on the area centralis over a broad range of gaze angles.

CONCLUSIONS

Severing and reattaching the tendons of the extraocular muscles affect some as-yet-unknown combination of central nervous system processes producing the above results. This new procedure may prove effective in patients with CN with either no null, a null at primary position, or a time-varying null (due to asymmetric, (a)periodic, alternating nystagmus). We infer from our results in an achiasmatic dog that tenotomy is the probable cause of the damping documented in human CN after Anderson-Kestenbaum procedures and should also damp CN and SSN in achiasma in humans. It may also prove useful in acquired nystagmus to reduce oscillopsia. The success of tenotomy in damping nystagmus in this animal suggests that the proprioceptive feedback loop has a more important role in ocular-motor control than has been appreciated. Finally, we propose a modified bimedial recession procedure, on the basis of the damping effects of tenotomy.

A double-blind controlled study of gabapentin and baclofen as treatment for acquired nystagmus

We conducted a double-blind crossover trial comparing gabapentin (up to 900 mg/day) to baclofen (up to 30 mg/day) as therapy for acquired nystagmus in 21 patients. We measured visual acuity and the nystagmus before, and at the end of, 2 weeks on each medication. For a group of 15 patients with acquired pendular nystagmus (APN), visual acuity improved significantly with gabapentin, but not with baclofen. Gabapentin significantly reduced APN median eye speed in all three planes, but baclofen did so only in the vertical plane. In 10 patients with APN, the reduction of nystagmus with gabapentin was substantial and 8 of these elected to continue taking the drug. In 6 patients with downbeat or torsional downbeat nystagmus, changes in median slow-phase eye speed were less consistent with both drugs, either increasing or decreasing, and being dependent on viewing conditions. Only 1 patient showed consistent reduction of median eye speed, and this was achieved by either drug. Our findings suggest that gabapentin may be an effective treatment for many patients with APN and that occasional patients with downbeat nystagmus will respond to gabapentin or baclofen.

Treatment of abnormal eye movements that impair vision: strategies based on current concepts of physiology and pharmacology

Certain abnormal eye movements, especially pathological nystagmus, degrade vision and cause illusory motion of the seen environment. These symptoms are due to excessive movement of images of stationary objects on the retina. Recently, the pathophysiology underlying several types of nystagmus and saccadic oscillations was better defined by the development of animal models and by experimental pharmacological studies. Despite this, few reliable therapies are currently available for these abnormal eye movements. In clinical studies, a number of drugs reportedly helped individual patients, but few drugs have been subjected to double-blind trials. An alternative approach to pharmacological suppression of abnormal eye movements is optical stabilization of images on the retina, which is helpful in selected patients. Weakening of the extraocular muscles, using botulinum toxin or surgery, is prone to cause diplopia and may induce plastic-adaptive changes that render the effect temporary. In some patients, treatment of an underlying condition, such as the Arnold-Chiari malformation, reduces nystagmus and improves vision. There is a need for multicenter trials to evaluate systematically potential treatments of abnormal eye movements that impair vision.

Upbeat nystagmus influenced by posture: report of two cases

Two cases of vertical gaze nystagmus, which were influenced by posture are reported. In both cases, upbeat nystagmus (UBN) on forward gaze in upright and supine positions changed to downbeat nystagmus (DBN) in prone position. Convergence had no influence on the vertical nystagmus. A CT scan revealed an atrophy of the anterior vermis of the cerebellum in the first case. The UBN of the second case was suspected to be associated with lesions in the brachium conjunctivum. The authors concluded that both UBN and DBN were not completely separate, but they could coexist in cases with certain lesions in the posterior cranial fossa.

Miotic Adie's pupils

Two young adults, aged 24 and 31, had a long history of small, poorly reactive pupils. There was no history of large pupils, and a review of old photographs confirmed 10 and 5 years, respectively, of miosis. Both were found to have bilateral tonic pupils that were supersensitive to diluted pilocarpine. Although it is possible that they had an unusually early onset of bilateral Adie's syndrome with dilated pupils that was not noticed, it is suggested that some patients might have primary miotic Adie's pupils without ever passing through a mydriatic phase.

Two cases of downbeat nystagmus and oscillopsia associated with carbamazepine

Downbeat nystagmus is often associated with structural lesions at the craniocervical junction, but has occasionally been reported as a manifestation of metabolic imbalance or drug intoxication. We recorded the eye movements of two patients with reversible downbeat nystagmus related to carbamazepine therapy. The nystagmus of both patients resolved after reduction of the serum carbamazepine levels. Neuroradiologic investigations including magnetic resonance imaging scans in both patients showed no evidence of intracranial abnormality. In patients with downbeat nystagmus who are taking anticonvulsant medications, consideration should be given to reduction in dose before further investigation is undertaken.

The use of clonazepam in the treatment of nystagmus-induced oscillopsia

The effect of clonazepam was studied in ten patients with nystagmus-induced oscillopsia due to downbeating or other primary position nystagmus. A 1-2-mg single-dose clonazepam test was used to determine whether long-term clonazepam therapy was indicated and to help distinguish between visual loss from underlying retinal or optic nerve disease and visual loss due to the nystagmus itself. With the single-dose clonazepam test, nystagmus was eliminated in 6 of 10 patients in the primary position of gaze and in 7 of 10 patients in downgaze. In all positions of gaze in all patients there was significant reduction in nystagmus intensity and slow phase velocity. Symptoms of oscillopsia were reduced or eliminated in all patients, and 7 of 8 patients with reduced visual acuity had clinical improvement. Guidelines are presented for the use of clonazepam in a single-dose clonazepam test and for long-term therapy.