A Cortical Substrate for Square-Wave Jerks in Progressive Supranuclear Palsy

Non-nystagmus hyperkinetic eye movement disorders

BACKGROUND

While nystagmus is an involuntary ocular movement relatively frequent, well described, and easily recognized by most practitioners, non-nystagmus hyperkinetic eye movement disorders (NHEMD) are less obvious and can be overlooked. NHEMD may arise from intrinsic abnormalities in ocular muscles and oculomotor nerves, brain and brainstem lesions, systemic diseases, dysimmune disorders, drugs or can even be functional in nature. Given that some treatable disorders initially manifest with NHEMD, their knowledge becomes crucial.

AIMS

This review aims to offer a practical and comprehensive guide to recognize specific types of NHEMD, to choose the appropriate diagnostic tests and treatments.

RESULTS

The review approaches individual NHEMD based on the location of anatomical lesions and the underlying pathophysiological mechanisms; therefore, it begins with those arising from abnormalities in extraocular muscles or oculomotor nerves (as for example, superior oblique myokymia and ocular neuromyotonia), then moves to NHEMD due to brainstem and brain involvement (as for example, ocular bobbing, opsoclonus, and tonic downward gaze deviation). Lastly, functional NHEMD and nonnystagmus ocular hyperkinesias associated with specific neurological disorders, such as Parkinson's disease or blepharospasm will be considered.

CONCLUSION

Overall, the review offers a comprehensive reappraisal of hyperkinetic disorders of eye motility.

Brainstem and cerebellar radiological findings in progressive supranuclear palsy

Progressive supranuclear palsy is a sporadic neurodegenerative 4-repeat tauopathy associated with significant morbidity. Heterogeneity of symptom expression among this group is increasingly recognized, reflecting variable tau spread and neurodegeneration. Clinical manifestations consist of debilitating and rapidly progressive motor, oculomotor, speech, cognitive and affective impairments. Core pathological changes are noted with a predominance in the midbrain and basal ganglia; however, spread to the more caudal brainstem and cerebellar regions is reported at various stages. Accordingly, whilst midbrain atrophy is the best recognized supportive imaging finding, quantitative neuroimaging studies using MRI and PET approaches have revealed a wider profile of brain abnormalities in cohorts of individuals with progressive supranuclear palsy. This expanded neurobiological scope of disease may account for individual heterogeneity and may highlight additional biological markers that are relevant to diagnosing and tracking the illness. Additionally, there is increasing understanding of the diverse cognitive, affective and speech functions of the cerebellum, which may be implicated in progressive supranuclear palsy beyond current recognition. In this review, we undertake a systematic literature search and summary of in vivo structural and functional neuroimaging findings in the brainstem and cerebellum in progressive supranuclear palsy to date. Novel and multimodal imaging techniques have emerged over recent years, which reveal several infratentorial alterations beyond midbrain atrophy in progressive supranuclear palsy. Most saliently, there is evidence for volume loss and microstructural damage in the pons, middle cerebellar peduncles and cerebellar cortex and deep nuclei, reported alongside recognized midbrain and superior cerebellar peduncle changes. Whilst the literature supporting the presence of these features is not unanimous, the evidence base is compelling, including correlations with disease progression, severity or variant differences. A smaller number of studies report on abnormalities in MRI measures of iron deposition, neuromelanin, viscoelasticity and the glymphatic system involving the infratentorial regions. Molecular imaging studies have also shown increased uptake of tau tracer in the midbrain and cerebellar dentate nucleus, although concern remains regarding possible off-target binding. Imaging of other molecular targets has been sparse, but reports of neurotransmitter, inflammatory and synaptic density alterations in cerebellar and brainstem regions are available. Taken together, there is an established evidence base of in vivo imaging alterations in the brainstem and cerebellum which highlights that midbrain atrophy is often accompanied by other infratentorial alterations in people with progressive supranuclear palsy. Further research examining the contribution of these features to clinical morbidity and inter-individual variability in symptom expression is warranted.

Abnormal eye movements: relationship with clinical symptoms and predictive value for Alzheimer's disease

Background

Abnormal eye movements occur at the early stages of Alzheimer's disease (AD). However, the characteristics of abnormal eye movements of patients with AD and their relationship with clinical symptoms remain inconsistent, and their predictive value for diagnosing and monitoring the progression of AD remains unclear.

Methods

A total of 42 normal controls, 63 patients with mild cognitive impairment due to AD (AD-MCI), and 49 patients with dementia due to AD (AD-D) were recruited. Eye movements were assessed using the EyeKnow eye-tracking and analysis system. Cognitive function, neuropsychiatric symptoms, and activities of daily living were evaluated using various rating scales, and correlation analyses and receiver operating characteristic curves were performed.

Results

Patients with AD exhibited increased number of offsets and offset degrees, prolonged offset duration, and decreased accuracy in lateral fixation; reduced accuracy, prolonged saccadic duration, and decreased velocity in prosaccade; decreased accuracy and corrected rate, prolonged corrected antisaccadic duration, and reduced velocity in antisaccade; and reduced accuracy and increased inhibition failures in memory saccade. Eye movement parameters were correlated with global cognition and the cognitive domains of memory, language, attention, visuospatial ability, execution function, and activities of daily living. Subgroup analysis indicated that the associations between eye movements and clinical symptoms in patients with AD were influenced by disease severity and history of diabetes. In the AD-D and AD with diabetes groups, these associations diminished. Nevertheless, the associations persisted in the AD-MCI and AD without diabetes groups. The areas under the curves for predicting AD, AD-MCI, and AD-D were 0.835, 0.737, and 0.899, respectively (all p < 0.05).

Conclusion

Patients with AD exhibit distinct patterns of abnormal eye movements. Abnormal eye movements are significantly correlated with global cognition, multiple cognitive domains, and activities of daily living. Abnormal eye movements have a considerable predictive value for the diagnosis and progression of AD.

Changes in saccadic intrusions over time as an objective biomarker to follow ALS disease progression

Objective: Saccadic Intrusions (SIs) are abnormal eye movements during gaze fixation. Studies have indicated the clinical relevance of SIs, especially of square wave jerks (SWJ) in ALS. We used a software-based platform to extract SIs as a part of an interventional drug trial. The objective was to examine SIs' change over time as a potential biomarker of ALS disease progression. Methods: 28 ALS patients (61.95 ± 8.6 years) were assessed with the revised ALS Functional Rating Scale (ALSFRS-R) and with an oculometric test. Changes of SIs over time and correlations with ALSFRS-R and its bulbar subscale were calculated. A power calculation was conducted to understand the practical implications of results. Results: A significant increase of SWJ over trial duration was observed, with an increase in frequency (mean rise of 0.14 ± 0.28, p < 0.01), amplitude (0.001 ± 0.0016 degrees, p < 0.005), overall duration of SWJ (0.13 ± 0.25, in %, p < 0.01), and in their relative part out of all intrusions (0.18 ± 0.32, in %, p < 0.005). Negative correlations were found with the bulbar subscale (R=-0.43, -0.41, -0.39 and -0.47, respectively, p < 0.001). The required sample size for observing a 40% reduction in bulbar aspects when using the oculometric test (α = 0.05 and β = 0.8), was found to be 150 patients per arm, compared with 200 patients using the bulbar subscale. Conclusions: Evaluation of saccadic intrusions during fixation was able to detect disease progression over time, correlated with ALSFRS-R bulbar subscale. Eye movements can potentially serve as an objective biomarker in ALS clinical trials and reduce the required sample size to show clinical effect of therapies.

Systematic assessment of square-wave jerks in progressive supranuclear palsy: a video-oculographic study

BACKGROUND

The presence of frequent macro-square-wave jerks (SWJs) has been recently included in the diagnostic criteria for progressive supranuclear palsy (PSP). The aim of the current video-oculographic study was to systematically assess the presence and features of SWJs during a brief fixation task in PSP, in comparison with Parkinson's disease (PD) patients and healthy controls (HC).

METHODS

Thirty-eight PSP patients, 55 PD patients and 40 HC were enrolled in the study. All patients underwent a video-oculographic (VOG) examination including a 5-s fixation task, and the number, duration and amplitude of SWJs were recorded. The diagnostic performance of several SWJs parameters were then compared in distinguishing PSP from PD patients and controls.

RESULTS

PSP patients showed a higher number and amplitude of SWJs compared to PD patients and controls. At least two SWJs within the 5-s fixation task were observed in 81.6% of PSP patients, 52.7% of PD patients and 25% of HC. The SWJs amplitude was the parameter showing the highest performances in distinguishing PSP from PD (AUC: 0.78) and HC (AUC: 0.88), outperforming the SWJ number and duration. The SWJ amplitude was larger in PSP-Richardson's syndrome than in PSP-Parkinsonism patients, while no difference was found between PSP patients with different degrees of vertical ocular motor dysfunction.

CONCLUSIONS

This video-oculographic study provides robust evidence of larger SWJs number and amplitude in PSP than in PD patients, with some potential for differential diagnosis, supporting the inclusion of this ocular sign in PSP criteria.

Detecting Abnormal Eye Movements in Patients with Neurodegenerative Diseases - Current Insights

This review delineates the ocular motor disturbances across a spectrum of neurodegenerative disorders, including Alzheimer's Disease (AD) and related disorders (ADRD), Parkinson's Disease (PD), atypical parkinsonism, and others, leveraging advancements in eye-tracking technology for enhanced diagnostic precision. We delve into the different classes of eye movements, their clinical assessment, and specific abnormalities manifesting in these diseases, highlighting the nuanced differences and shared patterns. For instance, AD and ADRD are characterized by increased saccadic latencies and instability in fixation, while PD features saccadic hypometria and mild smooth pursuit impairments. Atypical parkinsonism, notably Progressive Supranuclear Palsy (PSP) and Corticobasal Syndrome (CBS), presents with distinct ocular motor signatures such as vertical supranuclear gaze palsy and saccadic apraxia, respectively. Our review underscores the diagnostic value of eye movement analysis in differentiating between these disorders and also posits the existence of underlying common pathological mechanisms. We discuss how eye movements have potential as biomarkers for neurodegenerative diseases but also some of the existing limitations.

Clinical utility of square-wave jerks in neurology and psychiatry

Human eye fixation is steadily interrupted by small, physiological or abnormal, eye movements. Square-wave jerks (SWJ) are the most common saccadic intrusion which can be readily seen at the bedside and also quantified using oculographic techniques. Various neurological, neuropsychiatric and psychiatric disorders display abnormal fixational eye movement patterns characterized by frequent SWJ. For the clinician, SWJ are particularly important because they can be readily observed at the bedside. Here, we will discuss the pathological conditions that present with SWJ and explore the expanding body of literature suggesting that SWJ may serve as a potential indicator for various clinical conditions.

Sensorimotor and inhibitory control in aging FMR1 premutation carriers

Aging FMR1 premutation carriers are at risk of developing neurodegenerative disorders, including fragile X-associated tremor/ataxia syndrome (FXTAS), and there is a need to identify biomarkers that can aid in identification and treatment of these disorders. While FXTAS is more common in males than females, females can develop the disease, and some evidence suggests that patterns of impairment may differ across sexes. Few studies include females with symptoms of FXTAS, and as a result, little information is available on key phenotypes for tracking disease risk and progression in female premutation carriers. Our aim was to examine quantitative motor and cognitive traits in aging premutation carriers. We administered oculomotor tests of visually guided/reactive saccades (motor) and antisaccades (cognitive control) in 22 premutation carriers (73% female) and 32 age- and sex-matched healthy controls. Neither reactive saccade latency nor accuracy differed between groups. FMR1 premutation carriers showed increased antisaccade latencies relative to controls, both when considering males and females together and when analyzing females separately. Reduced saccade accuracy and increased antisaccade latency each were associated with more severe clinically rated neuromotor impairments. Findings indicate that together male and female premutation carriers show a reduced ability to rapidly exert volitional control over prepotent responses and that quantitative differences in oculomotor behavior, including control of visually guided and antisaccades, may track with FXTAS - related degeneration in male and female premutation carriers.

A biomarker and endophenotype for anorexia nervosa?

OBJECTIVE

Recent research has suggested that a type of atypical eye movement, called square wave jerks, together with anxiety, may distinguish individuals with anorexia nervosa from those without anorexia nervosa and may represent a biomarker and endophenotype for the illness. The aim of this study was to identify the presence of this proposed marker in individuals currently with anorexia nervosa relative to healthy controls, and to identify the state independence and heritability of this putative marker by exploring whether it also exists in individuals who are weight-restored from anorexia nervosa and first-degree relatives (i.e. sisters of people with anorexia nervosa).

METHODS

Data from 80 female participants (20/group: current anorexia nervosa, weight-restored from anorexia nervosa, sisters of people with anorexia nervosa and healthy controls) were analysed. Square wave jerk rate was acquired during a fixation task, and anxiety was measured with the State Trait Anxiety Inventory.

RESULTS

Current anorexia nervosa, weight-restored from anorexia nervosa and sisters of people with anorexia nervosa groups made significantly more square wave jerks than healthy controls, but did not differ from one another. Square wave jerk rate and anxiety were found to discriminate groups with exceptionally high accuracy (current anorexia nervosa vs healthy control = 92.5%; weight-restored from anorexia nervosa vs healthy control = 77.5%; sisters of people with anorexia nervosa vs healthy control = 77.5%; p < .001).

CONCLUSION

The combination of square wave jerk rate and anxiety was found to be a promising two-element marker for anorexia nervosa, and has the potential to be used as a biomarker or endophenotype to identify people at risk of anorexia nervosa and inform future treatments.

Oculomotor abnormalities and its association with sleep stages in progressive supranuclear palsy

BACKGROUND

Oculomotor abnormalities are one of the cardinal clinical features of progressive supranuclear palsy (PSP). Vertical saccadic slowing is an early sign of PSP. The association between oculomotor abnormalities and sleep architecture has not been studied so far.

OBJECTIVES

To study the association of oculomotor abnormalities of PSP with the sleep stages by using video polysomnography (vPSG).

METHODS

This was a cross-sectional single-center study. Twenty-two patients with PSP and 15 age and gender-matched controls were recruited. Saccades, vestibulo-ocular reflex, and optokinetic nystagmus were assessed and graded clinically in all patients and one overnight vPSG was done in all cases.

RESULTS

Vertical saccades, upward more than downwards, were affected in all cases. While horizontal saccades were normal only in 41% of cases. Vertical optokinetic nystagmus (OKN) was affected in all cases. Horizontal OKN was normal in 36% of patients. The vertical upward saccades had a negative correlation with N1% and duration (r = -0.418; p = 0.05, r = -0.457; p = 0.03), N3% and duration (r = -0.486; p = 0.02, r = -0.510; p = 0.01), REM% (r = -0.449; p = 0.04), total sleep time (r = -0.487; p = 0.02) and sleep efficiency (r = -0.444; p = 0.04). There was a positive correlation between horizontal OKN and sleep onset latency (r = 0.432; p = 0.05).

CONCLUSIONS

Vertical saccadic restriction in PSP has significant negative correlation with total sleep time and sleep efficiency. The oculomotor and sleep abnormalities in PSP are probably interlinked and their assessment is useful in determining the characteristics of the disease.

Eye Movement Abnormalities in Amyotrophic Lateral Sclerosis

It is generally believed that eye movements are completely spared in amyotrophic lateral sclerosis (ALS). Although a series of eye movement abnormalities has been recognized in recent years, the findings are highly controversial, and bulbar disabilities should be considered in relation to eye movement abnormalities. The present study aimed to determine whether eye movement abnormalities are present in ALS and, if so, to investigate their characteristics and their association with bulbar disability in ALS patients. A total of 60 patients and 30 controls were recruited and underwent the standardized evaluations of the oculomotor system using videonystagmography. Square-wave jerks (OR: 16.20, 95% CI: 3.50−74.95, p < 0.001) and abnormal cogwheeling during smooth pursuit (OR: 14.04, 95% CI: 3.00−65.75, p = 0.001) were more frequently observed in ALS patients than in the control subjects. In subgroup analyses, square-wave jerks (OR: 26.51, 95% CI: 2.83−248.05, p = 0.004) and abnormal cogwheeling during smooth pursuit (OR: 6.56, 95% CI: 1.19−36.16, p = 0.031) were found to be more common in ALS patients with bulbar involvement (n = 44) than in those without bulbar involvement (n = 16). There were no significant differences in the investigated eye movement parameters between bulbar-onset (n = 12) and spinal-onset patients (n = 48). ALS patients showed a range of eye movement abnormalities, affecting mainly the ocular fixation and smooth pursuit systems. Our pioneering study indicates that the region of involvement could better indicate the pathophysiological essence of the abnormalities than the type of onset pattern in ALS. Eye movement abnormalities may be potential clinical markers for objectively evaluating upper brainstem or supratentorial cerebral lesion neurodegeneration in ALS.

Ocular Motor Abnormalities in Anti-IgLON5 Disease

Objective

Anti-IgLON5 disease forms an interface between neuroinflammation and neurodegeneration and includes clinical phenotypes that are often similar to those of neurodegenerative diseases. An early diagnosis of patients with anti-IgLON5 disease and differentiation from neurodegenerative diseases is necessary and may have therapeutic implications.

Methods

In our small sample size study we investigated oculomotor function as a differentiating factor between anti-IgLON5 disease and neurodegenerative disorders. We examined ocular motor and vestibular function in four patients suffering from anti-IgLON5 disease using video-oculography (VOG) and a computer-controlled rotational chair system (sampling rate 60 Hz) and compared the data with those from ten age-matched patients suffering from progressive supranuclear palsy (PSP) and healthy controls (CON).

Results

Patients suffering from anti-IgLON5 disease differed from PSP most strikingly in terms of saccade velocity and accuracy, the presence of square wave jerks (SWJ) (anti-IgLON5 0/4 vs. PSP 9/10) and the clinical finding of supranuclear gaze palsy (anti-IgLON5 1/4). The presence of nystagmus, analysis of smooth pursuit eye movements, VOR and VOR suppression was reliable to differentiate between the two disease entities. Clear differences in all parameters, although not always significant, were found between all patients and CON.

Discussion

We conclude that the use of VOG as a tool for clinical neurophysiological assessment can be helpful in differentiating between patients with PSP and patients with anti-IgLON5 disease. VOG could have particular value in patients with suspected PSP and lack of typical Parkinson’s characteristics. future trials are indispensable to assess the potential of oculomotor function as a biomarker in anti-IgLON5 disease.

Preserved eye movements in adults with spinal muscular atrophy

INTRODUCTION

Spinal muscular atrophy (SMA) most prominently affects proximal limb and bulbar muscles. Despite older case descriptions, ocular motor neuron palsies or other oculomotor abnormalities are not considered part of the phenotype.

METHODS

We investigated oculomotor function by testing saccadic eye movements of 15 patients with SMA. Their performance was compared with that of age-matched healthy controls. Horizontal rightward and leftward saccades were recorded by means of video-oculography, whereas subjects looked at light-emitting diode targets placed at ±5°, ±10°, and ±15° eccentricities.

RESULTS

No differences in saccade amplitude gains, peak velocities, peak velocity-to-amplitude ratios, or durations were observed between controls and patients. More specifically, for 5° target eccentricities, patients had a mean saccadic peak velocity of 153°/s, whereas for 10° and 15° these values were 268°/s and 298°/s, respectively. The corresponding mean peak velocities of the control group were 151°/s, 264°/s, and 291°/s.

DISCUSSION

Our results indicate that patients with SMA perform fast and accurate horizontal saccades without evidence of extraocular muscle weakness. These quantitative oculomotor data corroborate clinical experience that neuro-ophthalmic symptoms in SMA are not common and, if present, should prompt suspicion for an alternative neuromuscular disorder.

Central nystagmus in progressive supranuclear palsy: A neglected clinical feature?

BACKGROUND

Progressive supranuclear palsy (PSP) features parkinsonism characterized by early postural instability, falls and prominent eye movement abnormalities that consist of saccadic slowing, followed by gaze limitation. Nystagmus is not considered typical for PSP, being more commonly associated with multiple system atrophy.

OBJECTIVES

To describe the prevalence and phenomenology of nystagmus in patients with PSP.

METHODS

42 patients with probable PSP underwent detailed clinical eye movement examination. Patients with nystagmus performed video-nystagmography. T-test, Chi-Square test and Wilcoxon signed-rank test were used to test differences in demographic data, disease duration and PSP subtype between patients with and without nystagmus, and for analysis of video-nystagmographic data.

RESULTS

Among 42 patients with PSP, we identified 15 patients (35,7%) with gaze-evoked nystagmus, predominantly horizontal. Clinically, 10/15 patients had symmetrical or asymmetrical gaze - evoked nystagmus (Type 1), while 5/15 patients had dissociated gaze-evoked nystagmus related to internuclear ophthalmoplegia (Type 2). Nystagmus and eye movement abnormalities were further characterized by video-nystagmography. There was no significant difference in age, disease duration or PSP subtypes between patients with and without nystagmus.

CONCLUSION

Central nystagmus is present in more than a third of patients with progressive supranuclear palsy. It may present as symmetrical or asymmetrical gaze-evoked nystagmus or as dissociated gaze-evoked nystagmus related to internuclear ophthalmoplegia and probably arises from neurodegeneration of the neural integrator. Nystagmus in PSP has been a hitherto under-described feature and its presence should not deter clinicians from a diagnosis of PSP.