Anti-GAD Antibodies and Periodic Alternating Nystagmus

Quantitative Oculomotor Assessment in Hereditary Ataxia: Systematic Review and Consensus by the Ataxia Global Initiative Working Group on Digital-motor Biomarkers

Oculomotor deficits are common in hereditary ataxia, but disproportionally neglected in clinical ataxia scales and as outcome measures for interventional trials. Quantitative assessment of oculomotor function has become increasingly available and thus applicable in multicenter trials and offers the opportunity to capture severity and progression of oculomotor impairment in a sensitive and reliable manner. In this consensus paper of the Ataxia Global Initiative Working Group On Digital Oculomotor Biomarkers, based on a systematic literature review, we propose harmonized methodology and measurement parameters for the quantitative assessment of oculomotor function in natural-history studies and clinical trials in hereditary ataxia. MEDLINE was searched for articles reporting on oculomotor/vestibular properties in ataxia patients and a study-tailored quality-assessment was performed. One-hundred-and-seventeen articles reporting on subjects with genetically confirmed (n=1134) or suspected hereditary ataxia (n=198), and degenerative ataxias with sporadic presentation (n=480) were included and subject to data extraction. Based on robust discrimination from controls, correlation with disease-severity, sensitivity to change, and feasibility in international multicenter settings as prerequisite for clinical trials, we prioritize a core-set of five eye-movement types: (i) pursuit eye movements, (ii) saccadic eye movements, (iii) fixation, (iv) eccentric gaze holding, and (v) rotational vestibulo-ocular reflex. We provide detailed guidelines for their acquisition, and recommendations on the quantitative parameters to extract. Limitations include low study quality, heterogeneity in patient populations, and lack of longitudinal studies. Standardization of quantitative oculomotor assessments will facilitate their implementation, interpretation, and validation in clinical trials, and ultimately advance our understanding of the evolution of oculomotor network dysfunction in hereditary ataxias.

Novelties in Autoimmune and Paraneoplastic Cerebellar Ataxias: Twenty Years of Progresses

Major advances in our knowledge concerning autoimmune and paraneoplastic cerebellar ataxias have occurred in the last 20 years. The discovery of several neural antibodies represents an undeniable contribution to this field, especially those serving as good biomarkers of paraneoplastic neurological syndromes and those showing direct pathogenic effects. Yet, many patients still lack detectable or known antibodies, and also many antibodies have only been reported in few patients, which makes it difficult to define in detail their clinical value. Nevertheless, a notable progress has additionally been made in the clinical characterization of patients with the main neural antibodies, which, although typically present with a subacute pancerebellar syndrome, may also show either hyperacute or chronic onsets that complicate the differential diagnoses. However, prodromal and transient features could be useful clues for an early recognition, and extracerebellar involvement may also be highly indicative of the associated antibody. Moreover, important advances in our understanding of the pathogenesis of cerebellar ataxias include the description of antibody effects, especially those targeting cell-surface antigens, and first attempts to isolate antigen-specific T-cells. Furthermore, genetic predisposition seems relevant, although differently involved according to cancer association, with particular HLA observed in non-paraneoplastic cases and genetic abnormalities in the tumor cells in paraneoplastic ones. Finally, immune checkpoint inhibitors used as cancer immunotherapy may rarely induce cerebellar ataxias, but even this undesirable effect may in turn serve to shed some light on their physiopathology. Herein, we review the principal novelties of the last 20 years regarding autoimmune and paraneoplastic cerebellar ataxias.

Gaze-holding and anti-GAD antibody: prototypic heterogeneous motor dysfunction in immune disease

The variability in motor dysfunction is not uncommon in autoimmune disorders. Antibody-mediated system-wide malfunction or effects on the neural network shared by two independent pathophysiological processes can cause such heterogeneity. We tested this prediction for motor dysfunction during gaze holding in 11 patients with increased titers of glutamic acid decarboxylase (anti-GAD) antibody. High-resolution oculography measured horizontal and vertical eye positions. The analysis was performed with customized signal processing algorithms. Downbeat and gaze-evoked nystagmus commonly coexisted; one patient had a combination of upbeat and gaze-evoked nystagmus. The nystagmus was associated with saccadic intrusions in 10 patients; all had squarewaves, but five also had saccadic oscillations. The nystagmus and saccadic intrusions, both in the same axis of eye rotations, were not uncommon. Tandem appearance of the episodes of nystagmus and saccadic intrusions suggested a coupling between the two abnormalities. We speculated a unifying framework where the anti-GAD antibody inhibited (GAD mediated) conversion of glutamate to gamma-aminobutyric acid (GABA). Paucity GABA and excess of glutamate cause nystagmus (less GABA) and high-frequency saccadic oscillations (excessive glutamate).

Ocular Motor and Vestibular Characteristics of Antiglutamic Acid Decarboxylase-Associated Neurologic Disorders

BACKGROUND

Antiglutamic acid decarboxylase (GAD)-associated neurologic disorders are rare, with varied presentations, including stiff-person syndrome (SPS) and cerebellar ataxia (CA). Vestibular and ocular motor (VOM) dysfunction can be the main presentation in a subset of patients.

METHODS

Retrospective review of the Johns Hopkins Hospital medical records from 1997 to 2018 identified a total of 22 patients with a diagnosis of anti-GAD-associated SPS or CA who had detailed VOM assessments. Eight had prominent VOM dysfunction at the initial symptom onset and were referred to neurology from ophthalmology or otolaryngology ("early dominant"). Fourteen patients had VOM dysfunction that was not their dominant presentation and were referred later in their disease course from neurology to neuro-ophthalmology ("nondominant"). We reviewed clinical history, immunological profiles, and VOM findings, including available video-oculography.

RESULTS

In the 8 patients with early dominant VOM dysfunction, the average age of symptom onset was 53 years, and 5 were men. The most common symptom was dizziness, followed by diplopia. Seven had features of CA, and 4 had additional features of SPS. None had a structural lesion on brain MRI accounting for their symptoms. The most common VOM abnormalities were downbeating and gaze-evoked nystagmus and saccadic pursuit. All received immune therapy and most received symptomatic therapy. Most experienced improvement in clinical outcome measures (modified Rankin scale and/or timed 25-foot walk test) or VOM function. By contrast, in the 14 patients in whom VOM dysfunction was nondominant, most had an SPS phenotype and were women. VOM abnormalities, when present, were more subtle, although mostly still consistent with cerebellar and/or brainstem dysfunction.

CONCLUSIONS

Individuals with anti-GAD-associated neurologic disorders may present with prominent VOM abnormalities at the initial symptom onset that localize to the cerebellum and/or brainstem. In our cohort, immune and symptomatic therapies improved clinical outcomes and symptomatology.

[Paraneoplastic ophthalmopathies]

Ocular paraneoplastic syndromes are rare conditions that can affect any part of the eye at any age. Thus, every ophthalmologist should be familiar with their management, as some of them may reveal severe, life-threatening conditions. These consist overwhelmingly of neuro-ophthalmological manifestations, affecting the optic nerve (paraneoplastic optic neuritis), retina (paraneoplastic retinopathy) or neurological pathways generating eye movements (saccadic intrusion, oculomotor palsy, nystagmus...); occasionally, they involve the anterior segment, orbit or uveal tract. As some of these manifestations appear to be quite common and non-specific, any systemic or especially neurologic comorbidities should increase suspicion. Treatment relies first on oncologic management, and then often more targeted therapy for the associated immune involvement.

Transient Neurological Symptoms Preceding Cerebellar Ataxia with Glutamic Acid Decarboxylase Antibodies

A prompt diagnosis and treatment of patients with autoimmune cerebellar ataxia (CA) with antibodies against glutamic acid decarboxylase (GAD-Abs) may lead to a better prognosis. Herein, we report prodromal transient neurological symptoms that should raise clinical suspicion of CA with GAD-Abs. We initially identified a 70-year-old man who presented a first acute episode of vertigo, diplopia, and ataxia lasting 2 weeks. Two months later, he experienced a similar episode along with new-onset gaze-evoked nystagmus. After 4 months, downbeat nystagmus, left limb dysmetria, and gait ataxia progressively appeared, and an autoimmune CA was diagnosed based on the positivity of GAD-Abs in serum and cerebrospinal fluid (CSF). We searched retrospectively for similar presentations in a cohort of 31 patients diagnosed with CA and GAD-Abs. We found 11 (35.4%) patients (all women, median age 62 years; 8/11 [72.7%] with autoimmune comorbidities) with transient neurological symptoms antedating CA onset by a median of 3 months, including vertigo in 9 (81.8%; described as paroxysmal in 8) and fluctuating diplopia in 3 (27.3%) patients. The identification of transient neurological symptoms of unknown etiology, such as paroxysmal vertigo and fluctuating diplopia, should lead to GAD-Abs testing in serum and CSF, especially in patients with autoimmune comorbidities.

Gravity-Independent Upbeat Nystagmus in Syndrome of Anti-GAD Antibodies

An autoimmune disorder of the central nervous system, stiff person syndrome, frequently presents with increased titers of 65KD anti-glutamic acid decarboxylase (anti-GAD) antibodies. The clinical phenomenology of this syndrome includes stiffness, ataxia, vertigo due to horizontal gaze-evoked and downbeat vertical nystagmus, and dysmetria of saccades and reaching movements. Here, we describe a novel phenomenology of syndrome of anti-GAD antibody, non-position-dependent upbeat nystagmus and superimposed horizontal gaze-evoked nystagmus. Lack of gravity dependence of primary position upbeat nystagmus, intense nystagmus on up-gaze, relatively stable gaze on downward orientation, and the exponentially decaying waveform suggests neural integrator dysfunction. The titer of anti-GAD in our patient (30 U/ml) was consistent with a variant called "low-titer anti-GAD syndrome". In addition of presenting as an unusual manifestation of a rare neurological syndrome, this case presents a neurochemical correlate of upbeat nystagmus in GABA-mediated control system involving horizontal and vertical neural integrators. Furthermore, the variant of "low-titer anti-GAD syndrome" suggests that GABAergic system may be affected at lower level or antibodies, and/or the epitopes of antibody in those with full-blown clinical syndrome, but low titers of anti-GAD may be different.

Stiff-Person Syndrome: A Case Report and Review of the Literature

AIM

To report a case of sudden onset vertical diplopia, blurred vision, and muscle spasms.

METHODS

This is a case report of a 57-year-old female who presented to the accident and emergency department with a one day history of vertical diplopia and a two week history of lower limb spasticity secondary to muscle spasms.

RESULTS

The patient had no significant medical or ocular history. Orthoptic investigation initially revealed a left inferior rectus (IR) underaction. Possible diagnoses at this point were thought to be isolated IR weakness, myasthenia gravis or skew deviation. An urgent MRI scan was arranged and blood tests were taken. MRI showed no abnormalities. Blood tests were normal, however, the acetylcholine receptor antibody serum test (ACH-R) was 0.43 nmol/L, which is at the high end of normal. At the follow-up visit, the IR weakness had deteriorated and the patient had also developed gaze-evoked nystagmus. An appointment with the neurologist and neuro-ophthalmologist was expedited. When the patient returned, she reported that her neurologist had diagnosed her with stiff-person syndrome (SPS). The patient had also developed a laterally alternating skew deviation and reported that she had undergone a course of intravenous immunoglobulin (IVIG). The patient was prescribed diazepam and gabapentin. Due to the lack of recovery, persistent diplopia and oscillopsia, monthly IVIG have been prescribed.

CONCLUSION

There is currently a paucity of literature relating to ophthalmic problems with SPS and how they are best treated. Previous reports have established that there is a link with myasthenia gravis, with many patients going on to develop myasthenia. Treatment of SPS is lacking large evidence-based studies. However, treatment with muscle relaxants and anticonvulsants has provided a good outcome for some. Further research is required to develop an evidence-based approach to treating the ophthalmological problems patients with SPS experience. This case report highlights the importance and value of orthoptists in investigating and monitoring patients with stiff-person syndrome.

Slow saccades in cerebellar disease

Eye movements are frequently considered diagnostic markers indicating involvement of the cerebellum. Impaired amplitude of saccades (saccade dysmetria), impaired gaze holding function (horizontal or downbeat nystagmus), and interrupted (choppy) pursuit are typically considered hallmarks of cerebellar disorders. While saccade dysmetria is a frequently considered abnormality, the velocity of saccades are rarely considered part of the constellation of cerebellar involvement. Reduced saccade velocity, frequently called “slow saccades” are typically seen in a classic disorder of the midbrain called progressive supranuclear palsy. It is also traditionally diagnostic of spinocerebellar ataxia type 2. In addition to its common causes, the slowness of vertical saccades is not rare in cerebellar disorders. Frequently this phenomenology is seen in multisystem involvement that substantially involves the cerebellum. In this review we will first discuss the physiological basis and the biological need for high saccade velocities. In subsequent sections we will discuss disorders of cerebellum that are known to cause slowing of saccades. We will then discuss possible pathology and novel therapeutic strategies.

Treatment of Cerebellar Ataxia in the Context of Systemic Diseases

Purpose of review The purpose of this review is to assess the evidence behind treatment regimens for cerebellar ataxias occurring in the context of systemic disease. We will address systemic conditions which are associated with specific involvement of the cerebellum (rather than widespread nervous system involvement) and those conditions for which some degree of evidence of treatment response exists.

Recent findings We have divided systemic disorders affecting the cerebellum into systemic immunological disorders, endocrine and metabolic disorders and paraneoplastic. Recent studies have increased understanding of the range of cerebellar disorders associated with a systemic immunological condition. The identification of newer pathogenic antibodies has improved diagnosis in conditions which would have previously been labelled as idiopathic. However, their rarity and phenotypic variability makes defining optimal immunomodulatory treatment regimens challenging. There is some evidence for beneficial effects of immunomodulation, particularly in anti-GAD ataxia and Hashimoto’s encephalopathy, although, at this time, specific treatment regimens cannot be defined. Immune-mediated paraneoplastic cerebellar disorders show response to therapy dependent, to some extent, on the underlying pathogenic antibody. Much is still to be understood concerning treatment regimens for the ataxic manifestations of metabolic disorders, notably alcohol-induced cerebellar injury, which are common and which are associated with significant disability.

Summary Despite their rarity, cerebellar ataxias occurring in the context of systemic disease cause significant morbidity and better therapies are required to improve outcomes associated with these conditions.

Clinical Approach to Supranuclear Brainstem Saccadic Gaze Palsies

Failure of brainstem supranuclear centers for saccadic eye movements results in the clinical presence of a brainstem-mediated supranuclear saccadic gaze palsy (SGP), which is manifested as slowing of saccades with or without range of motion limitation of eye movements and as loss of quick phases of optokinetic nystagmus. Limitation in the range of motion of eye movements is typically worse with saccades than with smooth pursuit and is overcome with vestibular–ocular reflexive eye movements. The differential diagnosis of SGPs is broad, although acute-onset SGP is most often from brainstem infarction and chronic vertical SGP is most commonly caused by the neurodegenerative condition progressive supranuclear palsy. In this review, we discuss the brainstem anatomy and physiology of the brainstem saccade-generating network; we discuss the clinical features of SGPs, with an emphasis on insights from quantitative ocular motor recordings; and we consider the broad differential diagnosis of SGPs.

Cerebellar disease associated with anti-glutamic acid decarboxylase antibodies: review

Several neurological syndromes have been recognized associated to GAD antibodies. Among those disorders, cerebellar ataxia (CA) is one of the most common, along with stiff-person syndrome. Patients with GAD associated CA present with a progressive pancerebellar syndrome, with a subacute or chronic evolution, along with other neurological manifestations such as stiffness, oculomotor dysfunction, epilepsy, and cognitive dysfunction. These symptoms may be preceded by the so-called "brainstem attacks", where manifestations consistent with transient dysfunction of the brainstem may be observed. These patients frequently have extra-neurologic autoimmune manifestations such as diabetes mellitus type 1, polyendocrine autoimmune syndrome, pernicious anemia, vitiligo, etc. A proportion of patients may present with an underlying neoplasia, but the course is less aggressive than in those patients with classical paraneoplastic CA with onconeural antibodies. The diagnosis is based on the present of high serum and CSF titers of GAD antibodies, with intrathecal production of such antibodies. Treatment is aimed to decrease the immunological response with intravenous immunoglobulin, steroids, rituximab and oral immunosuppressive drugs. A subacute presentation and rapid initiation of immunotherapy seem to be the predictors of a favorable clinical response.

Atypical periodic alternating nystagmus responding to high-dose intravenous immunoglobulins: a case report

BACKGROUND

Acquired periodic alternating nystagmus (PAN) is a rare but well-defined syndrome that consists of a horizontal nystagmus that cyclically reverses its direction. PAN can be caused by degenerative, neoplastic, or toxic diseases of the cerebellum and, in a few cases, by subacute cerebellar ataxia of immune origin.

CASE PRESENTATION

A 44-year-old man came to our attention because of rapidly progressive gait instability and blurred vision. Clinical examination showed PAN and a mild pancerebellar syndrome. Eye movement recordings disclosed a short cycle PAN with significant slow-phase velocity only in darkness. Under the effect of a γ-aminobutyric acid type B (GABA_B) agonist, PAN was not modified. Right after treatment with intravenous immunoglobulin (IVIg) was started, PAN was essentially eliminated. Three months after last dose of IVIg, this nystagmus reappeared.

CONCLUSIONS

IVIg resolved PAN in this patient. This finding may point to an autoimmune mechanism underlying this patient's nystagmus. This case suggests that the usefulness of IVIg at treating PAN might be worth a consideration in similar clinical settings.

Clinical characteristics of patients with cerebellar ataxia associated with anti-GAD antibodies

ABSTRACT The enzyme glutamic acid decarboxylase (GAD), present in GABAergic neurons and in pancreatic beta cells, catalyzes the conversion of gamma-aminobutyric acid (GABA). The cerebellum is highly susceptible to immune-mediated mechanisms, with the potentially treatable autoimmune cerebellar ataxia associated with the GAD antibody (CA-GAD-ab) being a rare, albeit increasingly detected condition. Few cases of CA-GAD-ab have been described. Methods This retrospective and descriptive study evaluated the clinical characteristics and outcomes of patients with CA-GAD-ab. Result Three patients with cerebellar ataxia, high GAD-ab titers and autoimmune endocrine disease were identified. Patients 1 and 2 had classic stiff person syndrome and insidious-onset cerebellar ataxia, while Patient 3 had pure cerebellar ataxia with subacute onset. Patients received intravenous immunoglobulin therapy with no response in Patients 1 and 3 and partial recovery in Patient 2. Conclusion CA-GAD-ab is rare and its clinical presentation may hamper diagnosis. Clinicians should be able to recognize this potentially treatable autoimmune cerebellar ataxia.

Basic and translational neuro-ophthalmology of visually guided saccades: disorders of velocity

Introduction

Saccades are rapid, yoked eye movements in an effort to direct a target over fovea. The complex circuitry of saccadic eye movements has been exhaustively described. As a result clinicians can elegantly localize the pathology if it falls on the neuraxis responsible for saccades. Traditionally saccades are studied with their quantitative characteristics such as amplitude, velocity, duration, direction, latency and accuracy.

Areas covered

Amongst all subtypes, the physiology of the visually guided saccades is most extensively studied. Here we will review the basic and pertinent neuro-anatomy and physiology of visually guided saccade and then discuss common or classic disorders affecting the velocity of visually guided saccades. We will then discuss the basic mechanism for saccade slowing in these disorders.

Expert commentary

Prompt appreciation of disorders of saccade velocity is critical to reach appropriate diagnosis. Disorders of midbrain, cerebellum, or basal ganglia can lead to prolonged transition time during gaze shift and decreased saccade velocity.

Opsoclonus in a patient with increased titers of anti-GAD antibody provides proof for the conductance-based model of saccadic oscillations

Paucity in gamma-amino butyric acid (GABA) due to blockage in the action of glutamic acid decarboxylase (GAD), as seen in the syndrome of anti-GAD antibody, causes adult onset cerebellar ataxia, muscle rigidity, and episodic spasms. Downbeat nystagmus, saccadic dysmetria, impaired ocular pursuit, and impaired cancelation of vestibular ocular reflex are typical ocular motor deficits in patients with syndrome of anti-GAD antibody. We describe opsoclonus, in addition to downbeat nystagmus, in a patient with increased titers of anti-GAD antibody. Paucity in GABA leading to disinhibition to Purkinje target neurons at deep cerebellar and vestibular nuclei might have caused downbeat nystagmus in our patient. Anti-GAD antibody can also increase levels of glutamate the precursor of GABA and the substrate for the action of GAD. We propose that opsoclonus might be due to increased levels of glutamate and subsequent hyperexcitability of excitatory and inhibitory burst neurons leading to reverberation in their reciprocally innervating circuit.

Alternating skew deviation in association with anti-glutamic acid decarboxylase antibodies

The presence of an elevated anti-glutamic acid decarboxylase (GAD) antibody level has been associated with a number of eye movement abnormalities, as well as other findings including cerebellar ataxia and insulin dependent diabetes mellitus. Skew deviation in association with anti-GAD antibodies has not been previously reported. Here we report a case of alternating skew deviation along with cerebellar-brainstem signs in a patient with an elevated anti-GAD antibody titer. Follow-up neurologic evaluation after treatment with intravenous immunoglobulin revealed improvement in cerebellar-brainstem signs, while ophthalmic evaluation was stable.

Paraneoplastic disorders of the central and peripheral nervous systems

Paraneoplatic neurologic syndromes (PNS) have been seminally defined as acute or subacute neurological syndromes resulting from nervous system dysfunction that is remote from the site of a malignant neoplasm or its metastases. However, in respect to our current understanding of their pathogenesis we may redefine these disorders as cancer-related dysimmune neurologic syndromes. We first deal with the epidemiology and the pathogenesis of PNS, then the different classic PNS are reviewed with clinical features according to the associated onconeuronal antibodies. Finally, therapeutic approaches are discussed.

GABA-A receptor impairment in cerebellar ataxia with anti-glutamic acid decarboxylase antibodies

Antibodies against glutamic acid decarboxylase (GAD-Abs) are associated with cerebellar ataxia, which is refractory to treatment with GABAergic drugs. To investigate the GABAergic neuronal system in vivo, we performed a combined positron emission tomography (PET) study with [(11)C]-flumazenil and [(18)F]-fluorodeoxyglucose (FDG) in three patients with cerebellar ataxia with GAD-Abs. The GABA-A receptor function was investigated using flumazenil, which is a selective GABA-A receptor ligand, while FDG-PET using a three-dimensional stereotactic surface projection analysis was performed to estimate the metabolic rates of glucose (MRGlc) in the patients. GABAergic drugs showed no efficacy for the cerebellar ataxia in all three patients, and all three displayed a significant decrease in flumazenil binding in the cerebellum. No MRGlc decrease in the cerebellum was found in the two patients who presented with amelioration of cerebellar ataxia following intravenous immunoglobulin (IVIG) therapy, whereas a significant MRGlc decrease in the cerebellar hemisphere was observed in another patient who showed severe cerebellar atrophy on magnetic resonance images and no response to the IVIG therapy. The decreased flumazenil binding in the present patients indicated cerebellar GABA-A receptor impairment, which may be due to either neuronal cell loss, as demonstrated by the decreased MRGlc, or a dysfunction in GABAergic neuronal inhibition. Although GAD-Abs have been postulated to prevent the synthesis of GABA, resulting in decreased GABAergic transmission, the GABA-A receptor impairment may play another pathogenic role in cerebellar ataxia associated with GAD-Abs resulting in a condition refractory to GABAergic drug therapy.

Consensus paper: roles of the cerebellum in motor control--the diversity of ideas on cerebellar involvement in movement

Considerable progress has been made in developing models of cerebellar function in sensorimotor control, as well as in identifying key problems that are the focus of current investigation. In this consensus paper, we discuss the literature on the role of the cerebellar circuitry in motor control, bringing together a range of different viewpoints. The following topics are covered: oculomotor control, classical conditioning (evidence in animals and in humans), cerebellar control of motor speech, control of grip forces, control of voluntary limb movements, timing, sensorimotor synchronization, control of corticomotor excitability, control of movement-related sensory data acquisition, cerebro-cerebellar interaction in visuokinesthetic perception of hand movement, functional neuroimaging studies, and magnetoencephalographic mapping of cortico-cerebellar dynamics. While the field has yet to reach a consensus on the precise role played by the cerebellum in movement control, the literature has witnessed the emergence of broad proposals that address cerebellar function at multiple levels of analysis. This paper highlights the diversity of current opinion, providing a framework for debate and discussion on the role of this quintessential vertebrate structure.

No effects of anti-motion sickness drugs on vestibular evoked myogenic potentials outcome parameters

OBJECTIVE

To investigate the effects of meclizine (50 mg), baclofen (10 mg), cinnarizine (20 mg) + dimenhydrinate (40 mg), and promethazine (25 mg) + dextro-amphetamine (5 mg) on the parameters of the vestibular evoked myogenic potential (VEMP) test.

STUDY DESIGN

Double-blind placebo-controlled prospective randomized trial.

SETTING

University hospital.

SUBJECTS

Twenty-four (first block: baclofen versus placebo) and 20 healthy male subjects (second block: meclizine, cinnarizine + dimenhydrinate and promethazine + dextro-amphetamine versus placebo).

INTERVENTIONS

VEMP test.

MAIN OUTCOME MEASURES

Threshold, p13 and n23 latencies, p13-n23 latency difference, p13-n23 peak-to-peak amplitude, mean rectified voltage of the sternocleidomastoid muscle contraction and the corrected amplitude.

RESULTS

There were no clinically significant pharmacologic effects on the VEMP outcome parameters. However, there was a statistically significant left-right asymmetry after intake of the combination promethazine + d-amphetamine for the parameters p13 and latency difference.

CONCLUSION

The absence of clinically significant effects can be explained by the predominant presence of the target receptors for the applied drugs in the medial vestibular nucleus, which receives the lowest grade of saccular projections. It also can be hypothesized that the VEMP methodology and techniques in general do not allow determining pharmacologic effects in a healthy group of subjects because of a too small discriminative power. The left-right asymmetry can be explained by a depressive action of the drugs on the central compensation mechanisms. Because there were no significant differences between the VEMP parameters obtained after intake of the placebos of both blocks, we concluded that there were no training effects.

Clinical presentation of immune-mediated cerebellar ataxia

INTRODUCTION

Accumulation of recent clinical evidence indicates that the immune system plays an important role in some central nervous system diseases usually regarded as degenerative. The most striking example is paraneoplastic cerebellar ataxia (PCA), which is characterized by autoimmune cross-reaction between tumoral and nervous system antigens.

STATE OF THE ART

In the past 20 years, several antibodies directed against neuronal and tumoral antigens have been described in association with PCA, leading to the description of different subtypes of PCA based on the associated antibodies, the clinical course and the type of tumor. In some subtypes, cerebellar ataxia occurs in isolation, whereas in others, cerebellar ataxia is a syndrome that occurs in conjunction with extensive nervous system disease. Circulating antibodies have also been described in patients with non-paraneoplastic cerebellar ataxia (N-PCA), suggesting that the immune system may be involved in certain cases of sporadic cerebellar ataxia.

PERSPECTIVE

Immune-mediated cerebellar ataxia does not seem to be limited to paraneoplastic neurological syndromes. Further studies are however necessary to understand the exact pathophysiology of these disorders and offer effective treatments.

CONCLUSION

In this review, the clinical presentation of the different subtypes of potentially immune-mediated PCA and N-PCA will be described, and the associated tumors will be discussed.

Infantile aperiodic alternating nystagmus

BACKGROUND

This study identifies the clinical and ocular motility characteristics of the periodic and aperiodic forms of infantile alternating nystagmus (IAPAN) and establishes the range of electrophysiological and clinical characteristics while providing clues to its presence and pathophysiology.

METHODS

Seventy-eight patients with ocular oscillations consistent with IAPAN were reported. Outcome variables were: age, follow-up in months, vision, strabismus, other eye and systemic abnormalities, head position, periodicity, cycle and null period duration, foveation time, waveforms, and cycle symmetry.

RESULTS

Age range was 1 to 67 years, 50% had pure periodic and aperiodic forms, 46% had albinism, 26% had binocular acuity of 20/40 or greater, 72% had strabismus, 35% had amblyopia, 31% had other eye disease, 14% had systemic disease, 87% had an anomalous head posture, and 65% had binocular directional asymmetry. The periodic cycle averaged 224 seconds and the aperiodic cycle ranged from 2 to more than 300 seconds. One in three patients with strabismus and nystagmus periodicity had a static head posture.

CONCLUSION

Fifteen percent of the infantile nystagmus syndrome population had either the periodic or aperiodic form. A changing null period is often clinically missed because of long or irregular cycles, decreased acuity, associated strabismus, and either a nonexistent or inconsistent head posture. The changing null period is easier to recognize using eye movement recordings or if the non-preferred eye is occluded and the preferred eye is examined with the head straight and gaze in primary position for at least 5 to 7 minutes. The recognition of this variant has profound treatment implications.

Epilepsy and cerebellar ataxia associated with anti-glutamic acid decarboxylase antibodies

Anti-glutamic acid decarboxylase (GAD) antibodies are described in stiff-person syndrome and also in other neurological syndromes, including cerebellar ataxia and epilepsy. This paper reports the case of a patient who had chronic focal epilepsy, upbeat nystagmus and cerebellar ataxia, associated with a polyautoimmune response including anti-GAD antibodies. Both gait and nystagmus improved markedly after immunosuppressive treatment with corticosteroids and azathioprine. After the introduction of benzodiazepines, previously refractory seizures were completely controlled. Anti-GAD antibodies should be actively sought out in pharmacoresistant epilepsy, particularly if other neurological abnormalities are present. Combined treatment with immunosuppressants and γhydroxybutyric acidergic agents may be highly effective.

Epilepsy and cerebellar ataxia associated with anti-glutamic acid decarboxylase antibodies

Anti-glutamic acid decarboxylase (GAD) antibodies are described in stiff-person syndrome and also in other neurological syndromes, including cerebellar ataxia and epilepsy. This paper reports the case of a patient who had chronic focal epilepsy, upbeat nystagmus and cerebellar ataxia, associated with a polyautoimmune response including anti-GAD antibodies. Both gait and nystagmus improved markedly after immunosuppressive treatment with corticosteroids and azathioprine. After the introduction of benzodiazepines, previously refractory seizures were completely controlled. Anti-GAD antibodies should be actively sought out in pharmacoresistant epilepsy, particularly if other neurological abnormalities are present. Combined treatment with immunosuppressants and gammahydroxybutyric acidergic agents may be highly effective.

Localizing forms of nystagmus: Symptoms, diagnosis, and treatment

Nystagmus is a rhythmic oscillation of the eyes that may be acquired or congenital. The symptoms of acquired nystagmus include blurred vision and oscillopsia. Most patients with congenital nystagmus do not have oscillopsia symptoms. Several forms of nystagmus have localizing value and any neuroimaging should be directed to the topographic localization suggested by the morphology of the nystagmus and any accompanying localizing signs. Several optical, medical, and surgical treatments have been used with some success in specific forms of nystagmus.