Cerebellar transcranial direct current stimulation in spinocerebellar ataxia type 3 (SCA3-tDCS): rationale and protocol of a randomized, double-blind, sham-controlled study

The potential value of disease-modifying therapy in patients with spinocerebellar ataxia type 1: an early health economic modeling study

OBJECTIVE

There currently is no disease-modifying therapy for spinocerebellar ataxia type 1 (SCA1). Genetic interventions, such as RNA-based therapies, are being developed but those currently available are very expensive. Early evaluation of costs and benefits is, therefore, crucial. By developing a health economic model, we aimed to provide first insights into the potential cost-effectiveness of RNA-based therapies for SCA1 in the Netherlands.

METHODS

We simulated disease progression of individuals with SCA1 using a patient-level state-transition model. Five hypothetical treatment strategies with different start and endpoints and level of effectiveness (5-50% reduction in disease progression) were evaluated. Consequences of each strategy were measured in terms of quality-adjusted life years (QALYs), survival, healthcare costs, and maximum costs to be cost effective.

RESULTS

Most QALYs (6.68) are gained when therapy starts during the pre-ataxic stage and continues during the entire disease course. Incremental costs are lowest (- €14,048) if therapy is stopped when the severe ataxia stage is reached. The maximum costs per year to be cost-effective are €19,630 in the "stop after moderate ataxia stage" strategy at 50% effectiveness.

DISCUSSION

Our model indicates that the maximum price for a hypothetical therapy to be cost-effective is considerably lower than currently available RNA-based therapies. Most value for money can be gained by slowing progression in the early and moderate stages of SCA1 and by stopping therapy upon entering the severe ataxia stage. To allow for such a strategy, it is crucial to identify individuals in early stages of disease, preferably just before symptom onset.

Progression of Clinical and Eye Movement Markers in Preataxic Carriers of Machado-Joseph Disease

BACKGROUND

Little is known about preclinical stages of Machado-Joseph disease, a polyglutamine disorder characterized by progressive adult-onset ataxia.

OBJECTIVE

We aimed to describe the longitudinal progression of clinical and oculomotor variables in the preataxic phase of disease.

METHODS

Carriers and noncarriers were assessed at three visits. Preataxic carriers (Scale for Assessment and Rating of Ataxia score < 3) expected to start ataxia in ≤4 years were considered near onset (PAN). Progressions of ataxic and preataxic carriers, considering status at the end of the study, were described according to the start (or its prediction) of gait ataxia (TimeToAfterOnset) and according to the study time.

RESULTS

A total of 35 ataxics, 38 preataxics, and 22 noncarriers were included. The "TimeToAfterOnset" timeline showed that Neurological Examination Scale for Spinocerebellar Ataxias (NESSCA; effect size, 0.09), Inventory of Non-Ataxia Symptoms (INAS0.07), and the vestibulo-ocular reflex gain (0.12) progressed in preataxic carriers, and that most slopes accelerate in PAN, turning similar to those of ataxics. In the study time, NESSCA (1.36) and vertical pursuit gain (1.17) significantly worsened in PAN, and 6 of 11 PANs converted to ataxia. For a clinical trial with 80% power and 2-year duration, 57 PANs are needed in each study arm to detect a 50% reduction in the conversion rate.

CONCLUSIONS

NESSCA, INAS, vestibulo-ocular reflex, and vertical pursuit gains significantly worsened in the preataxic phase. The "TimeToAfterOnset" timeline unveiled that slopes of most variables are small in preataxics but increase and reach the ataxic slopes from 4 years before the onset of ataxia. For future trials in preataxic carriers, we recommend recruiting PANs and using the conversion rate as the primary outcome. © 2022 International Parkinson and Movement Disorder Society.

Cerebellar Transcranial Direct Current Stimulation in Spinocerebellar Ataxia Type 3: a Randomized, Double-Blind, Sham-Controlled Trial

Repeated sessions of cerebellar anodal transcranial direct current stimulation (tDCS) have been suggested to modulate cerebellar-motor cortex (M1) connectivity and decrease ataxia severity. However, therapeutic trials involving etiologically homogeneous groups of ataxia patients are lacking. The objective of this study was to investigate if a two-week regimen of daily cerebellar tDCS sessions diminishes ataxia and non-motor symptom severity and alters cerebellar-M1 connectivity in individuals with spinocerebellar ataxia type 3 (SCA3). We conducted a randomized, double-blind, sham-controlled trial in which twenty mildly to moderately affected SCA3 patients received ten sessions of real or sham cerebellar tDCS (i.e., five days per week for two consecutive weeks). Effects were evaluated after two weeks, three months, six months, and twelve months. Change in Scale for the Assessment and Rating of Ataxia (SARA) score after two weeks was defined as the primary endpoint. Static posturography, SCA Functional Index tests, various patient-reported outcome measures, the cerebellar cognitive affective syndrome scale, and paired-pulse transcranial magnetic stimulation to examine cerebellar brain inhibition (CBI) served as secondary endpoints. Absolute change in SARA score did not differ between both trial arms at any of the time points. We observed significant short-term improvements in several motor, cognitive, and patient-reported outcomes after the last stimulation session in both groups but no treatment effects in favor of real tDCS. Nonetheless, some of the patients in the intervention arm showed a sustained reduction in SARA score lasting six or even twelve months, indicating interindividual variability in treatment response. CBI, which reflects the functional integrity of the cerebellothalamocortical tract, remained unchanged after ten tDCS sessions. Albeit exploratory, there was some indication for between-group differences in SARA speech score after six and twelve months and in the number of extracerebellar signs after three and six months. Taken together, our study does not provide evidence that a two-week treatment with daily cerebellar tDCS sessions reduces ataxia severity or restores cerebellar-M1 connectivity in early-to-middle-stage SCA3 patients at the group level. In order to potentially increase therapeutic efficacy, further research is warranted to identify individual predictors of symptomatic improvement.

Cerebellar transcranial direct current stimulation modulates timing but not acquisition of conditioned eyeblink responses in SCA3 patients

BACKGROUND

Delay eyeblink conditioning is an extensively studied motor learning paradigm that critically depends on the integrity of the cerebellum. In healthy individuals, modulation of cerebellar excitability using transcranial direct current stimulation (tDCS) has been reported to alter the acquisition and/or timing of conditioned eyeblink responses (CRs). It remains unknown whether such effects can also be elicited in patients with cerebellar disorders.

OBJECTIVE

To investigate if repeated sessions of cerebellar tDCS modify acquisition and/or timing of CRs in patients with spinocerebellar ataxia type 3 (SCA3) and to evaluate possible associations between disease severity measures and eyeblink conditioning parameters.

METHODS

Delay eyeblink conditioning was examined in 20 mildly to moderately affected individuals with SCA3 and 31 healthy controls. After the baseline session, patients were randomly assigned to receive ten sessions of cerebellar anodal tDCS or sham tDCS (i.e., five days per week for two consecutive weeks). Patients and investigators were blinded to treatment allocation. The same eyeblink conditioning protocol was administered directly after the last tDCS session. The Scale for the Assessment and Rating of Ataxia (SARA), cerebellar cognitive affective syndrome scale (CCAS-S), and disease duration were used as clinical measures of disease severity.

RESULTS

At baseline, SCA3 patients exhibited significantly fewer CRs than healthy controls. Acquisition was inversely associated with the number of failed CCAS-S test items but not with SARA score. Onset and peak latencies of CRs were longer in SCA3 patients and correlated with disease duration. Repeated sessions of cerebellar anodal tDCS did not affect CR acquisition, but had a significant treatment effect on both timing parameters. While a shift of CRs toward the conditioned stimulus was observed in the sham group (i.e., timing became more similar to that of healthy controls, presumably reflecting the effect of a second eyeblink conditioning session), anodal tDCS induced a shift of CRs in the opposite direction (i.e., toward the unconditioned stimulus).

CONCLUSION

Our findings provide the first evidence that cerebellar tDCS is capable of modifying cerebellar function in SCA3 patients. Future studies should assess whether this intervention similarly modulates temporal processing in other degenerative ataxias.

Current and Emerging Treatment Modalities for Spinocerebellar Ataxias

INTRODUCTION

Spinocerebellar ataxias (SCA) are a group of rare neurodegenerative diseases that dramatically affect the lives of affected individuals and their families. Despite having a clear understanding of SCA's etiology, there are no current symptomatic or neuroprotective treatments approved by the FDA.

AREAS COVERED

Research efforts have greatly expanded the possibilities for potential treatments, including both pharmacological and non-pharmacological interventions. Great attention is also being given to novel therapeutics based in gene therapy, neurostimulation, and molecular targeting. This review article will address the current advances in the treatment of SCA and what potential interventions are on the horizon.

EXPERT OPINION

SCA is a highly complex and multifaceted disease family with the majority of research emphasizing symptomatic pharmacologic therapies. As pre-clinical trials for SCA and clinical trials for other neurodegenerative conditions illuminate the efficacy of disease modifying therapies such as AAV-mediated gene therapy and ASOs, the potential for addressing SCA at the pre-symptomatic stage is increasingly promising.

Effects of Anodal Cerebellar Transcranial Direct Current Stimulation on Movements in Patients with Cerebellar Ataxias: A Systematic Review

Cerebellar transcranial direct current stimulation (cerebellar tDCS) is a promising therapy for cerebellar ataxias and has attracted increasing attention from researchers and clinicians. A timely systematic review focusing on randomized sham-controlled trials and repeated measures studies is warranted. This study was to systematically review existing evidence regarding effects of anodal cerebellar tDCS on movements in patients with cerebellar ataxias. The searched databases included Web of Science, MEDLINE, PsycINFO, CINAHL, EMBASE, Cochrane Library, and EBSCOhost. Methodological quality of the selected studies was assessed using the Physiotherapy Evidence Database scale. Five studies with 86 patients were identified. Among these, four studies showed positive effects of anodal cerebellar tDCS. Specifically, anodal cerebellar tDCS decreased disease severity and improved finger dexterity and quality of life in patients, but showed incongruent effects on gait control and balance, which may be due to heterogeneity of research participants and choices of measures. The protocols of anodal cerebellar tDCS that improved movements in patients commonly placed the anode over the whole cerebellum and provided ten 2-mA 20-min stimulation sessions. The results may show preliminary evidence that anodal cerebellar tDCS is beneficial to reducing disease severity and improving finger dexterity and quality of life in patients, which lays the groundwork for future studies further examining responses in the cerebello-thalamo-cortical pathway. An increase in sample size, the use of homogeneous patient groups, exploration of the optimal stimulation protocol, and investigation of detailed neural mechanisms are clearly needed in future studies.

Exploring the clinical meaningfulness of the Scale for the Assessment and Rating of Ataxia: A comparison of patient and physician perspectives at the item level

BACKGROUND

The Scale for the Assessment and Rating of Ataxia (SARA) is commonly used as the primary outcome measure in therapeutic trials. Driven by spontaneous comments from ataxia patients participating in a trial, we aimed to examine the clinical meaningfulness of the SARA from their perspective.

METHODS

Twenty mildly to moderately affected individuals with spinocerebellar ataxia type 3 (SARA score 11.3 ± 4.1) completed a custom-designed survey. SARA item scores were compared with self-reported complaints in everyday life. Discrepancies between SARA ratings and patients' daily life experiences were reported as "overestimation" (i.e., a SARA item score more than 0, but no corresponding complaints) or "underestimation" (i.e., a SARA item score of 0, yet accompanying complaints).

RESULTS

Patient-physician discrepancies were present in essentially all SARA items except for gait. The mean number of overestimated SARA points per patient was 3.1 ± 2.1. Underestimation occurred less frequently, but was relatively common in stance and fast alternating hand movements. Three quarters of patients marked gait as the most valuable SARA item, while the remaining 25% selected stance.

CONCLUSION

On average, a quarter of total SARA score does not reflect meaningful impairments from a patient's perspective. Our data suggest that it is doubtful whether potential improvements at some of the items will be perceived as comparably important by mildly to moderately affected ataxia patients. These observations question the utility of delta SARA score as the most appropriate primary endpoint in clinical trials and call for the addition of outcome measures, such as the Patient Global Impression of Change scale and validated ataxia-specific patient-reported outcome measures.

Motor and cognitive outcomes of cerebello-spinal stimulation in neurodegenerative ataxia

Cerebellar ataxias represent a heterogeneous group of disabling disorders characterized by motor and cognitive disturbances, for which no effective treatment is currently available. In this randomized, double-blind, sham-controlled trial, followed by an open-label phase, we investigated whether treatment with cerebello-spinal transcranial direct current stimulation (tDCS) could improve both motor and cognitive symptoms in patients with neurodegenerative ataxia at short and long-term. Sixty-one patients were randomized in two groups for the first controlled phase. At baseline (T0), Group 1 received placebo stimulation (sham tDCS) while Group 2 received anodal cerebellar tDCS and cathodal spinal tDCS (real tDCS) for 5 days/week for two weeks (T1), with a 12-week (T2) follow-up (randomized, double-blind, sham controlled phase). At the 12-week follow-up (T2), all patients (Group 1 and Group 2) received a second treatment of anodal cerebellar tDCS and cathodal spinal tDCS (real tDCS) for 5 days/week for two weeks, with a 14-week (T3), 24-week (T4), 36-week (T5) and 52-week follow-up (T6) (open-label phase). At each time point, a clinical, neuropsychological and neurophysiological evaluation was performed. Cerebellar-motor cortex connectivity was evaluated using transcranial magnetic stimulation (TMS). We observed a significant improvement in all motor scores (scale for the assessment and rating of ataxia, international cooperative ataxia rating scale), in cognition (evaluated with the cerebellar cognitive affective syndrome scale), in quality-of-life scores, in motor cortex excitability and in cerebellar inhibition after real tDCS compared to sham stimulation and compared to baseline (T0), both at short and long-term. We observed an addon-effect after two repeated treatments with real tDCS compared to a single treatment with real tDCS. The improvement at motor and cognitive scores correlated with the restoration of cerebellar inhibition evaluated with TMS. Cerebello-spinal tDCS represents a promising therapeutic approach for both motor and cognitive symptoms in patients with neurodegenerative ataxia, a still orphan disorder of any pharmacological intervention.

A narrative review on non-invasive stimulation of the cerebellum in neurological diseases

IMPORTANCE

The cerebellum plays an important role in motor, cognitive, and affective functions owing to its dense interconnections with basal ganglia and cerebral cortex. This review aimed at summarizing the non-invasive cerebellar stimulation (NICS) approaches used to modulate cerebellar output and treat cerebellar dysfunction in the motor domain.

OBSERVATION

The utility of NICS in the treatment of cerebellar and non-cerebellar neurological diseases (including Parkinson's disease, dementia, cerebellar ataxia, and stroke) is discussed. NICS induces meaningful clinical effects from repeated sessions alone in both cerebellar and non-cerebellar diseases. However, there are no conclusive data on this issue and several concerns need to be still addressed before NICS could be considered a valuable, standard therapeutic tool.

CONCLUSIONS AND RELEVANCE

Even though some challenges must be overcome to adopt NICS in a wider clinical setting, this tool might become a useful strategy to help patients with lesions in the cerebellum and cerebral areas that are connected with the cerebellum whether one could enhance cerebellar activity with the intention of facilitating the cerebellum and the entire, related network, rather than attempting to facilitate a partially damaged cortical region or inhibiting the homologs' contralateral area. The different outcome of each approach would depend on the residual functional reserve of the cerebellum, which is confirmed as a critical element to be probed preliminary in order to define the best patient-tailored NICS.

Discordance Between Patient-Reported Outcomes and Physician-Rated Motor Symptom Severity in Early-to-Middle-Stage Spinocerebellar Ataxia Type 3

Assessment of patient-reported outcome measures (PROMs) in spinocerebellar ataxias (SCAs) could provide valuable insights into self-perceived health status. Although they are considered additional endpoints in future clinical trials, determinants and interactions of different PROMs in early disease stages remain largely unknown. The aims of the present study were to evaluate health-related quality of life, depressive symptoms, fatigue, and physical activity in mildly to moderately affected SCA3 patients and to examine interrelations between these PROMs and objective disease severity indices. Twenty SCA3 patients and twenty healthy controls of comparable age and sex completed the EQ-5D-5L, Patient Health Questionnaire-9, Profile of Mood States, and International Physical Activity Questionnaire. Disease severity was quantified by the Scale for the Assessment and Rating of Ataxia (SARA) and Inventory of Non-Ataxia Signs (INAS). Mildly to moderately affected SCA3 patients reported lower quality of life (p = 0.049), more depressive symptoms (p = 0.028), and higher levels of fatigue (p = 0.001) than healthy controls. The amount of physical activity did not differ between both groups. Linear regression analyses revealed that quality of life was primarily determined by fatigue and not by ataxia severity, while physical activity was independently associated with SARA score and INAS count but not fatigue. Depressive symptoms were related to disease duration and fatigue but not to markers of motor disease progression. Taken together, decreased quality of life, increased levels of fatigue, and a higher number of depressive symptoms do not merely reflect motor impairment in early-to-middle-stage SCA3 patients. The observed discordance between patient-reported and clinician-based outcomes indicates that these measures genuinely evaluate distinct aspects of disease and emphasizes their complementariness in therapeutic trials. By contrast, the volume of self-reported physical activity is not associated with fatigue, reflects both ataxia severity and extracerebellar involvement, and could therefore represent a useful marker of motor impairment in a home setting.

Inverse associations between cerebellar inhibition and motor impairment in spinocerebellar ataxia type 3

BACKGROUND

Cerebellar ataxia generally results from a lesion disrupting the corticopontocerebellar or cerebellothalamocortical tract. The cerebellar inhibition (CBI) paradigm represents a dual-coil transcranial magnetic stimulation protocol that interrogates the integrity of the latter pathway. Whether CBI has clinical relevance in ataxia patients remains largely unknown because associations with pertinent disease severity measures in etiologically homogeneous cohorts have not been previously examined.

OBJECTIVE

To investigate if CBI correlates with clinical and functional indices of disease severity in individuals with spinocerebellar ataxia type 3 (SCA3).

METHODS

CBI was assessed in fourteen SCA3 patients by paired-pulse cerebellar-motor cortex (M1) stimulation using interstimulus intervals of 3, 5, and 10 ms. Correlation coefficients were determined between CBI and ataxia severity, manual dexterity, and walking speed.

RESULTS

Suppression of M1 excitability occurred 5 ms following a contralateral cerebellar conditioning stimulus in SCA3 patients, but, on average, CBI was significantly reduced as compared to a healthy control group from the literature (p < 0.001). A significant association was found between decreased CBI levels and higher Scale for the Assessment and Rating of Ataxia (SARA) scores (r = -0.62, p = 0.019). CBI was negatively correlated with axial, appendicular, and speech subscores, as well as with nine-hole peg test performance (r = -0.69, p = 0.006). No association was observed between CBI and walking speed. As expected, there were no significant clinical-neurophysiological correlations at 3 and 10 ms interstimulus intervals.

CONCLUSION

Our results provide the first neurophysiological evidence for an inverse association between cerebellothalamocortical tract integrity, as reflected by reduced levels of CBI, and ataxia severity in SCA3 patients. Longitudinal studies are required to evaluate if CBI could serve as a marker of disease progression.

A word of hope for ataxia trials in COVID-19 time and beyond

The coronavirus disease 2019 (COVID-19) crisis confronted us, like many researchers worldwide, with an unforeseen challenge during the final stages of a randomized controlled trial involving ataxia patients. Institutional guidelines suddenly no longer allowed regular follow-up visits to take place, impeding the clinical evaluation of long-term outcomes. Here, we discuss the various scenarios that we considered in response to these imposed restrictions and share our experience of home video recording by dedicated, extensively instructed family members. Albeit somewhat unconventional at first glance, this last resort strategy enabled us to reliably assess the study's primary endpoint at the predefined point in time and hopefully encourages researchers in other ongoing ataxia trials to continue their activities. Remote assessments of ataxia severity may serve as a reasonable substitute in interventional trials beyond the current exceptional situation generated by the COVID-19 pandemic, but will require further investigation.

Non-invasive Transcranial Electrical Stimulation in Movement Disorders

Dysfunction within large-scale brain networks as the basis for movement disorders is an accepted hypothesis. The treatment options for restoring network function are limited. Non-invasive brain stimulation techniques such as repetitive transcranial magnetic stimulation are now being studied to modify the network. Transcranial electrical stimulation (tES) is also a portable, cost-effective, and non-invasive way of network modulation. Transcranial direct current stimulation and transcranial alternating current stimulation have been studied in Parkinson’s disease, dystonia, tremor, and ataxia. Transcranial pulsed current stimulation and transcranial random noise stimulation are not yet studied enough. The literature in the use of these techniques is intriguing, yet many unanswered questions remain. In this review, we highlight the studies using these four potential tES techniques and their electrophysiological basis and consider the therapeutic implication in the field of movement disorders. The objectives are to consolidate the current literature, demonstrate that these methods are feasible, and encourage the application of such techniques in the near future.

Non-Invasive Cerebellar Stimulation in Neurodegenerative Ataxia: A Literature Review

Cerebellar ataxias are a heterogenous group of degenerative disorders for which we currently lack effective and disease-modifying interventions. The field of non-invasive brain stimulation has made much progress in the development of specific stimulation protocols to modulate cerebellar excitability and try to restore the physiological activity of the cerebellum in patients with ataxia. In light of limited evidence-based pharmacologic and non-pharmacologic treatment options for patients with ataxia, several different non-invasive brain stimulation protocols have emerged, particularly employing repetitive transcranial magnetic stimulation (rTMS) or transcranial direct current stimulation (tDCS) techniques. In this review, we summarize the most relevant rTMS and tDCS therapeutic trials and discuss their implications in the care of patients with degenerative ataxias.

Supervised transcranial direct current stimulation (tDCS) at home: A guide for clinical research and practice

BACKGROUND

Transcranial direct current stimulation (tDCS) is a method of noninvasive neuromodulation and potential therapeutic tool to improve functioning and relieve symptoms across a range of central and peripheral nervous system conditions. Evidence suggests that the effects of tDCS are cumulative with consecutive daily applications needed to achieve clinically meaningful effects. Therefore, there is growing interest in delivering tDCS away from the clinic or research facility, usually at home.

OBJECTIVE

To provide a comprehensive guide to operationalize safe and responsible use of tDCS in home settings for both investigative and clinical use.

METHODS

Providing treatment at home can improve access and compliance by decreasing the burden of time and travel for patients and their caregivers, as well as to reach those in remote locations and/or living with more advanced disabilities.

RESULTS

To date, methodological approaches for at-home tDCS delivery have varied. After implementing the first basic guidelines for at-home tDCS in clinical trials, this work describes a comprehensive guide for facilitating safe and responsible use of tDCS in home settings enabling access for repeated administration over time.

CONCLUSION

These guidelines provide a reference and standard for practice when employing the use of tDCS outside of the clinic setting.

The role of the cerebellum in degenerative ataxias and essential tremor: Insights from noninvasive modulation of cerebellar activity

Over the last three decades, measuring and modulating cerebellar activity and its connectivity with other brain regions has become an emerging research topic in clinical neuroscience. The most important connection is the cerebellothalamocortical pathway, which can be functionally interrogated using a paired‐pulse transcranial magnetic stimulation paradigm. Cerebellar brain inhibition reflects the magnitude of suppression of motor cortex excitability after stimulating the contralateral cerebellar hemisphere and therefore represents a neurophysiological marker of the integrity of the efferent cerebellar tract. Observations that cerebellar noninvasive stimulation techniques enhanced performance of certain motor and cognitive tasks in healthy individuals have inspired attempts to modulate cerebellar activity and connectivity in patients with cerebellar diseases in order to achieve clinical benefit. We here comprehensively explore the therapeutic potential of these techniques in two movement disorders characterized by prominent cerebellar involvement, namely the degenerative ataxias and essential tremor. The article aims to illustrate the (patho)physiological insights obtained from these studies and how these translate into clinical practice, where possible by addressing the association with cerebellar brain inhibition. Finally, possible explanations for some discordant interstudy findings, shortcomings in our current understanding, and recommendations for future research will be provided. © 2019 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.