Chronic deep brain stimulation for the treatment of tremor in multiple sclerosis: review and case reports

Brain stimulation for patients with multiple sclerosis: an umbrella review of therapeutic efficacy

Multiple sclerosis patients often experience various symptoms that can greatly impact their quality of life. There are various brain stimulation techniques that have been evaluated for their ability to reduce the symptoms of multiple sclerosis. However, there is inconsistency in the specific stimulation methods used and the symptoms targeted in the existing research. This umbrella review conducted in order to evaluate the effectiveness of brain stimulation and identify limitations and gaps for further research. In this umbrella review, we conducted a searched on Web of Knowledge, PubMed, and Scopus database. We specifically looked for reviews, with or without meta-analyses, that have investigated the effects of brain stimulation methods on symptoms of multiple sclerosis. All articles were examined by AMSTAR 2 (A Measure Tool to Assess Systematic Review 2). We identified 155 articles, of which 14 were eligible for inclusion. Of those, five were qualitative studies and nine were meta-analyses. Among the included studies, four examined the use of deep brain stimulation, while ten investigated the therapeutic potential of noninvasive brain stimulation. Considering the heterogeneity of studies, the current evidence suggests that repetitive transcranial magnetic stimulation may be effective in treating pain and improving motor function, while transcranial direct current stimulation may be useful in alleviating fatigue and enhancing certain aspects of cognitive performance. Deep brain stimulation, on the other hand, appears to be effective in reducing tremors. However, further research is warranted to validate these findings and address the existing limitations in the field.

Patient selection and outcome of deep brain stimulation for multiple sclerosis-associated tremor

INTRODUCTION

Tremor is a disabling symptom of multiple sclerosis (MS), with limited treatment modalities. Thalamic ventral-intermediate-nucleus (VIM) deep brain stimulation (DBS) is a method of neuromodulation. We describe the long-term outcomes of our carefully selected patients who underwent VIM DBS for their MS-associated tremor.

METHODS

Patients were referred from the regional neurology units. Pre-operative assessments included suitability for anesthesia, tremor quantification by the Fahn-Tolosa-Marin scores, and quality-of-life (EQ5D) measures. Exclusion criteria included prominent cerebellar symptoms such as ataxia and dysmetria, intracranial pathology such as ventriculomegaly, cerebellar plaques and thalamic abnormality, and comorbid psychiatric symptoms. Seven patients (3M:4F) underwent DBS for MS-associated tremor between September 2013 and February 2019. Mean age was 42 years (±SD 8 years). DBS was performed at a mean of 13 years (±SD 9 years) after diagnosis of MS.

RESULTS

There were no postoperative surgical complications. All patients showed improvement in FTM tremor scores, by up to 61% at 6 months postoperatively. There was an improvement of 30-175% in quality-of-life scores at 6 months. Improvement of tremor and quality of life, over baseline, was sustained over a long period of follow-up (mean 26.6 months ± SD 20.7 months), including our longest duration at 72 months.

CONCLUSION

With careful selection, DBS is a safe, efficacious intervention for MS-tremor and can positively impact on tremor and quality of life, with effects over a long period. As patients live longer with MS and the advent of new therapies, DBS should be considered for selected patients.

Movement Disorders in Multiple Sclerosis: An Update

Background:

Multiple sclerosis (MS), a subset of chronic primary inflammatory demyelinating disorders of the central nervous system, is closely associated with various movement disorders. These disorders may be due to MS pathophysiology or be coincidental. This review describes the full spectrum of movement disorders in MS with their possible mechanistic pathways and therapeutic modalities.

Methods:

The authors conducted a narrative literature review by searching for ‘multiple sclerosis’ and the specific movement disorder on PubMed until October 2021. Relevant articles were screened, selected, and included in the review according to groups of movement disorders.

Results:

The most prevalent movement disorders described in MS include restless leg syndrome, tremor, ataxia, parkinsonism, paroxysmal dyskinesias, chorea and ballism, facial myokymia, including hemifacial spasm and spastic paretic hemifacial contracture, tics, and tourettism. The anatomical basis of some of these disorders is poorly understood; however, the link between them and MS is supported by clinical and neuroimaging evidence. Treatment options are disorder-specific and often multidisciplinary, including pharmacological, surgical, and physical therapies.

Discussion:

Movements disorders in MS involve multiple pathophysiological processes and anatomical pathways. Since these disorders can be the presenting symptoms, they may aid in early diagnosis and managing the patient, including monitoring disease progression. Treatment of these disorders is a challenge. Further work needs to be done to understand the prevalence and the pathophysiological mechanisms responsible for movement disorders in MS.

Tremor in Multiple Sclerosis-An Overview and Future Perspectives

Tremor is an important and common symptom in patients with multiple sclerosis (MS). It constituted one of the three core features of MS triad described by Charcot in the last century. Tremor could have a drastic impact on patients' quality of life. This paper provides an overview of tremor in MS and future perspectives with a particular emphasis on its epidemiology (prevalence: 25-58%), clinical characteristics (i.e., large amplitude 2.5-7 Hz predominantly postural or intention tremor vs. exaggerated physiological tremor vs. pseudo-rhythmic activity arising from cerebellar dysfunction vs. psychogenic tremor), pathophysiological mechanisms (potential implication of cerebellum, cerebello-thalamo-cortical pathways, basal ganglia, and brainstem), assessment modalities (e.g., tremor rating scales, Stewart-Holmes maneuver, visual tracking, digitized spirography and accelerometric techniques, accelerometry-electromyography coupling), and therapeutic options (i.e., including pharmacological agents, botulinum toxin A injections; deep brain stimulation or thalamotomy reserved for severe, disabling, or pharmaco-resistant tremors). Some suggestions are provided to help overcome the unmet needs and guide future therapeutic and diagnostic studies in this complex disorder.

Deep Brain Stimulation for Multiple Sclerosis Tremor: A Meta-Analysis

OBJECTIVES

To examine the effect of deep brain stimulation (DBS) on multiple sclerosis (MS)-tremor, as measured by a normalized scale of tremor severity, with a meta-analysis of the published literature.

METHODS

Medline and EBSCO Host (January, 1998 to June, 2018) were systematically reviewed with librarian guidance, using the keywords "Deep brain stimulation" and "multiple sclerosis." Bibliographies and experts in the field were also consulted to identify missed articles. All therapeutic studies on DBS for MS-tremor, reported in the English language, within the study period were included. Papers that reported outcomes without a measure of central tendency and/or distribution were excluded. The papers were read in their entirety and graded for risk of bias according to the American Academy of Neurology (AAN) standards. To maximize statistical power, papers using different stimulation targets were grouped together. Outcomes were reported with the Fahn-Tolosa-Marin scale (FTM), the Bain-Finchley scale (CRS) and 3- and 4-point tremor severity scales and normalized with a Hedges g.

RESULTS

The search produced 13 studies suitable for meta-analysis. The random-effects meta-analysis showed that DBS improved the Hedges standardized mean tremor score by 2.86 (95%CI 2.03-3.70, p < .00001). Heterogeneity was high, with an I² of 84%, suggesting that random effects model is more appropriate. Adverse event rates varied from 8% to 50%.

CONCLUSIONS

This meta-analysis provides level III evidence that DBS may improve MS-related tremor as measured by standardized tremor severity scales.

Biomaterials and glia: Progress on designs to modulate neuroinflammation

Microglia are multi-functional cells that play a vital role in establishing and maintaining the function of the nervous system and determining the fate of neurons following injury or neuropathology. The roles of microglia are diverse and essential to the capacity of the nervous system to recover from injury, however sustained inflammation can limit recovery and drive chronic disease processes such as neurodegenerative disorders. When assessing implantable therapeutic devices in the central nervous system, an improved lifetime of the implant is considered achievable through the attenuation of microglial inflammation. Consequently, there is a tremendous underexplored potential in biomaterial and engineered design to modulate neuroinflammation for therapeutic benefit. Several strategies for improving device compatibility reviewed here include: biocompatible coatings, improved designs in finer and flexible shapes to reduce tissue shear-related scarring, and loading of anti-inflammatory drugs. Studies about microglial cell cultures in 3D hydrogels and nanoscaffolds to assess various injuries and disorders are also discussed. A variety of other microglia-targeting treatments are also reviewed, including nanoparticulate systems, cellular backpacks, and gold plinths, with the intention of delivering anti-inflammatory drugs by targeting the phagocytic nature of microglia. Overall, this review highlights recent advances in biomaterials targeting microglia and inflammatory function with the potential for improving implant rejection and biocompatibility studies. STATEMENT OF SIGNIFICANCE: Microglia are the resident immune cells of the central nervous system, and thus play a central role in the neuroinflammatory response against conditions than span acute injuries, neuropsychiatric disorders, and neurodegenerative disorders. This review article presents a summary of biomaterials research that target microglia and other glial cells in order to attenuate neuroinflammation, including but not limited to: design of mechanically compliant and biocompatible stimulation electrodes, hydrogels for high-throughput 3D modelling of nervous tissue, and uptake of nanoparticle drug delivery systems. The goal of this paper is to identify strengths and gaps in the relevant literature, and to promote further consideration of microglia behaviour and neuroinflammation in biomaterial design.

Pharmacological and Non-pharmacological Therapies of Cognitive Impairment in Multiple Sclerosis

Background

Cognitive impairment is one of the most important clinical features of neurodegenerative disorders including multiple sclerosis (MS). Conducted research shows that up to 65 percent of MS patients have cognitive deficits such as episodic memory, sustained attention, reduced verbal fluency; however, the cognitive MS domain is information processing speed. It is the first syndrome of cognitive dysfunction and the most widely affected in MS. Occasionally these impairments occur even before the appearance of physical symptoms.

Methods

Therefore, this review focused on the current status of our knowledge about possible methods of treatment cognitive impairment in MS patients including novel strategies. Research and online content was performed using Medline and EMBASE databases.

Results

The most recent research suggests that cognitive impairment is correlated with brain lesion volume and brain atrophy. The examination of the cognitive impairment is usually based on particular neuropsychological batteries. However, it can be not enough to make a precise diagnosis. This creates a demand to find markers that might be useful for identifying patients with risk of cognitive impairment at an early stage of the disease. Currently the most promising methods consist of neuroimaging indicators, such as diffusion tensor imaging, the magnetization transfer ratio, and N-acetyl aspartate levels. Diagnosis problems are strictly connected with treatment procedures. There are two main cognitive therapies: pharmacological (disease modifying drugs (DMD), symptomatic treatments) and non-pharmacological interventions that are focused on psychological and physical rehabilitation. Some trials have shown a positive association between physical activity and the cognitive function.

Conclusion

This article is an overview of the current state of knowledge related to cognition impairment treatment in MS. Additionally, novel strategies for cognitive impairments such as cryostimulation and other complementary methods are presented.

[What is new in symptomatic MS treatment: Part 1-introduction and methodical approach, ataxia and tremor]

The symptomatic treatment of multiple sclerosis (MS) nowadays is of similar importance as immunotherapy within a comprehensive concept of therapy of this chronic disease, since it contributes considerably to the reduction of disabilities in activities of daily living as well as social and occupational life. Moreover, symptomatic treatment is of great importance for amelioration of quality of life. Since our last survey of symptomatic MS treatment in 2004 and publication of the guidelines of the German Neurological Society and the Klinisches Kompetenznetz Multiple Sklerose (KKN‑MS) in 2014 several developments within the topics of mobility, bladder and sexual function, vision, fatigue, cognition and rehabilitation took place. These new findings together with further aspects of disease measures and overall treatment strategies of the respective symptoms, as well as treatment goals are introduced in a series of six individual contributions. Here, the topic will be introduced, the methodical approach will be explained, and the treatment of ataxia and tremor will be discussed.

Mesoscopic model of neuronal system deficits in Multiple Sclerosis

Multiple Sclerosis (MS) is a devastating autoimmune disease which deteriorates the connections in central nervous system (CNS) through the attacks to oligodendrocytes. Studying its origin and progression, in addition to clinical developments such as MRI brain images, cerebrospinal fluid (CSF) variation and quantitative measures of disability (EDSS), which sought to early diagnosis and efficient therapy, there is an increasing interest in developing computational models using the experimental data obtained from MS patients. From the perspective of mathematical modelling, although the origin of systemic symptoms might be attributed to cellular phenomena in microscopic level such as axonal demyelination, symptoms mainly are observed in macroscopic levels. How to fill the gap between these two levels of system modelling, however, remains as a challenge in systems biology studies. Trying to provide a conceptual framework to bridge between these two levels of modelling in systems biology, we have suggested a mesoscopic model composed of interacting neuronal population, which successfully replicates the changes in neuronal population synchrony due to MS progression.

Deep brain stimulation for the treatment of uncommon tremor syndromes

Introduction: Deep brain stimulation (DBS) has become a standard therapy for the treatment of select cases of medication refractory essential tremor and Parkinson’s disease however the effectiveness and long-term outcomes of DBS in other uncommon and complex tremor syndromes has not been well established. Traditionally, the ventralis intermedius nucleus (VIM) of the thalamus has been considered the main target for medically intractable tremors; however alternative brain regions and improvements in stereotactic techniques and hardware may soon change the horizon for treatment of complex tremors.

Areas covered: In this article, we conducted a PubMed search using different combinations between the terms ‘Uncommon tremors’, ‘Dystonic tremor’, ‘Holmes tremor’ ‘Midbrain tremor’, ‘Rubral tremor’, ‘Cerebellar tremor’, ‘outflow tremor’, ‘Multiple Sclerosis tremor’, ‘Post-traumatic tremor’, ‘Neuropathic tremor’, and ‘Deep Brain Stimulation/DBS’. Additionally, we examined and summarized the current state of evolving interventions for treatment of complex tremor syndromes.

Expertcommentary: Recently reported interventions for rare tremors include stimulation of the posterior subthalamic area, globus pallidus internus, ventralis oralis anterior/posterior thalamic subnuclei, and the use of dual lead stimulation in one or more of these targets. Treatment should be individualized and dictated by tremor phenomenology and associated clinical features.

Eligibility Criteria for Deep Brain Stimulation in Parkinson’s Disease, Tremor, and Dystonia

In this review, the available evidence to guide clinicians regarding eligibility for deep brain stimulation (DBS) in the main conditions in which these forms of therapy are generally indicated—Parkinson’s disease (PD), tremor, and dystonia—is presented. In general, the literature shows that DBS is effective for PD, essential tremor, and idiopathic dystonia. In these cases, key points in patient selection must include the level of disability and inability to manage symptoms using the best available medical therapy. Results are, however, still not optimal when dealing with other aetiologies, such as secondary tremors and symptomatic dystonia. Also, in PD, issues such as age and neuropsychiatric profile are still debatable parameters. Overall, currently available literature is able to guide physicians on basic aspects of patient selection and indications for DBS; however, a few points are still debatable and controversial. These issues should be refined and clarified in future studies.

Pallidal stimulation for Holmes tremor: clinical outcomes and single-unit recordings in 4 cases

OBJECT

Holmes tremor (HT) is characterized by irregular, low-frequency (< 4.5 Hz) tremor occurring at rest, with posture, and with certain actions, often affecting proximal muscles. Previous reports have tended to highlight the use of thalamic deep brain stimulation (DBS) in cases of medication-refractory HT. In this study, the authors report the clinical outcome and analysis of single-unit recordings in patients with medication-refractory HT treated with globus pallidus internus (GPi) DBS.

METHODS

The authors retrospectively reviewed the medical charts of 4 patients treated with pallidal DBS for medication-refractory HT at the University of California, San Francisco, and San Francisco Veterans Affairs Medical Center. Clinical outcomes were measured at baseline and after surgery using an abbreviated motor-severity Fahn-Tolosa-Marin (FTM) tremor rating scale. Intraoperative microelectrode recordings were performed with patients in the awake state. The neurophysiological characteristics identified in HT were then also compared with characteristics previously described in Parkinson's disease (PD) studied at the authors' institution.

RESULTS

The mean percentage improvement in tremor motor severity was 78.87% (range 59.9%–94.4%) as measured using the FTM tremor rating scale, with an average length of follow-up of 33.75 months (range 18–52 months). Twenty-eight GPi neurons were recorded intraoperatively in the resting state and 13 of these were also recorded during contralateral voluntary arm movement. The mean firing rate at rest in HT was 56.2 ± 28.5 Hz, and 63.5 ± 19.4 Hz with action, much lower than the GPi recordings in PD. GPi unit oscillations of 2–8 Hz were prominent in both patients with HT and those with PD, but in HT, unlike PD, these oscillations were not suppressed by voluntary movement.

CONCLUSIONS

The efficacy of GPi DBS exceeded that reported in prior studies of ventrolateral thalamus DBS and suggest GPi may be a better target for treating HT. These clinical and neurophysiological findings help illuminate evolving models of HT and highlight the importance of cerebellar–basal ganglia interactions.

Targeting the red nucleus for cerebellar tremor

Deep brain stimulation of the thalamus (and especially the ventral intermediate nucleus) does not significantly improve a drug-resistant, disabling cerebellar tremor. The dentato-rubro-olivary tract (Guillain-Mollaret triangle, including the red nucleus) is a subcortical loop that is critically involved in tremor genesis. We report the case of a 48-year-old female patient presenting with generalized cerebellar tremor caused by alcohol-related cerebellar degeneration. Resistance to pharmacological treatment and the severity of the symptoms prompted us to investigate the effects of bilateral deep brain stimulation of the red nucleus. Intra-operative microrecordings of the red nucleus revealed intense, irregular, tonic background activity but no rhythmic components that were synchronous with upper limb tremor. The postural component of the cerebellar tremor disappeared during insertion of the macro-electrodes and for a few minutes after stimulation, with no changes in the intentional (kinetic) component. Stimulation per se did not reduce postural or intentional tremor and was associated with dysautonomic symptoms (the voltage threshold for which was inversed related to the stimulation frequency). Our observations suggest that the red nucleus is (1) an important centre for the genesis of cerebellar tremor and thus (2) a possible target for drug-refractory tremor. Future research must determine how neuromodulation of the red nucleus can best be implemented in patients with cerebellar degeneration.

Shorter pulse generator longevity and more frequent stimulator adjustments with pallidal DBS for dystonia versus other movement disorders

BACKGROUND

Deep brain stimulation has become a routine therapy for movement disorders, but it is relatively invasive and costly. Although stimulation intensity relates to battery longevity, less is known about how diagnosis and stimulation target contribute to this clinical outcome. Here we evaluate battery longevity in movement disorders patients who were treated at a tertiary referral center.

OBJECTIVE

To compare single channel pulse generator longevity in patients with movement disorders.

METHODS

With Institutional Review Board approval, we evaluated 470 consecutive Soletra implants for routine care. Battery longevity was estimated with Kaplan-Meier analyses, and group comparisons were performed with the log rank mean test. The frequency of clinic encounters for ongoing care was evaluated across diagnoses with analysis of variance (ANOVA).

RESULTS

The mean pulse generator longevity was 44.9 ± 1.4 months. Pallidal DBS for dystonia was associated with shorter battery longevity than subthalamic and thalamic DBS for Parkinson's disease and essential tremor (28.1 ± 2.1 versus 47.1 ± 1.8 and 47.8 ± 2.6 months, respectively, mean ± standard error, P < 0.001), and dystonia patients required more frequent clinic visits for routine care (F = 6.0, P = 0.003). Pallidal DBS for Parkinson's disease and thalamic DBS for cerebellar outflow tremor were associated with shorter battery longevity, as well (35.3 ± 4.6 and 26.4 ± 4.3 months, respectively).

CONCLUSIONS

Pallidal DBS for dystonia was associated with shorter battery longevity and more frequent stimulator adjustments versus DBS for Parkinson's disease and essential tremor. Characteristics of the stimulation target and disease pathophysiology both likely contribute to battery longevity in patients with movement disorders.

Safety considerations for deep brain stimulation: review and analysis

Deep brain stimulation has emerged rapidly as an effective therapy for movement disorders. Deep brain stimulation includes an implanted brain electrode and a pacemaker-like implanted pulse generator. The clinical application of deep brain stimulation proceeded in the absence of clear understandings of its mechanisms of action or extensive preclinical studies of safety and efficacy. Post mortem studies suggest that there is a loss of neurons in proximity to the active electrode, but the resulting lesions are not sufficient to treat the disorder and efficacy requires continued stimulation. Overall complication rates can exceed 25%, and permanent neurologic sequelae result in 4-6% of cases. As the application of deep brain stimulation expands, it is critical to understand the origin of adverse events and the delivery of nondamaging stimulation.

Deep brain stimulation: indications and evidence

Deep brain stimulation is a minimally invasive targeted neurosurgical intervention that enables structures deep in the brain to be stimulated electrically by an implanted pacemaker. It has become the treatment of choice for Parkinson's disease, refractory to, or complicated by, drug therapy. Its efficacy has been demonstrated robustly by randomized, controlled clinical trials, with multiple novel brain targets having been discovered in the last 20 years. Multifarious clinical indications for deep brain stimulation now exist, including dystonia and tremor in movement disorders; depression, obsessive-compulsive disorder and Tourette's syndrome in psychiatry; epilepsy, cluster headache and chronic pain, including pain from stroke, amputation, trigeminal neuralgia and multiple sclerosis. Current research argues for novel indications, including hypertension and orthostatic hypotension. The development, principles, indications and effectiveness of the technique are reviewed here. While deep brain stimulation is a standard and widely accepted treatment for Parkinson's disease after 20 years of experience, in chronic pain it remains restricted to a handful of experienced, specialist centers willing to publish outcomes despite its use for over 50 years. Reasons are reviewed and novel approaches to appraising clinical evidence in functional neurosurgery are suggested.

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.

Treatment of symptoms in multiple sclerosis

The current focus regarding treatment of multiple sclerosis (MS) to be on therapies that may alter the course of the disease. Some of the evidence regarding the efficacy of these treatments is based on changes in the appearance of neuroimaging studies of the brain and spinal cord and not on the effect of these treatments on clinical symptomatology. Since most of our patients with MS continue to be symptomatic despite the use of immunomodulating agents, it is important for the treating neurologist to be familiar with treatments for these symptoms, many of which are extremely disabling to the patient. Knowing how to deal with common complaints/symptoms of MS enables us to better practice the art of neurological care.

Deep brain stimulation for other tremors, myoclonus, and chorea

Deep brain stimulation (DBS) is a well established treatment for essential tremor and for the tremor associated with Parkinson's disease. The efficacy of DBS in these common tremors has led some investigators to apply the technique to rarer tremors such as such as Holmes' tremor, posttraumatic tremor, orthostatic tremor, and the tremor associated with multiple sclerosis. Likewise, DBS of the thalamus and globus pallidus directly suppresses levodopa-induced dyskinesias in Parkinson's disease, suggesting the application of DBS to other hyperkinetic states such as Huntington's disease, tardive dyskinesia, and hemiballism. Myoclonus has also been treated with DBS, especially in cases where it is associated with dystonia. This chapter reviews the reported results of DBS for these conditions. Due to the rarity of these indications, most of the literature reviewed takes the form of case reports or small single-center case series.

Understanding tremor in multiple sclerosis: prevalence, pathological anatomy, and pharmacological and surgical approaches to treatment

Background

Given that tremor is one of the most prevalent and disabling features of multiple sclerosis (MS), we will review the most significant milestones in tremor in this disease in recent years, focusing on prevalence, clinical features, anatomical basis, and treatment.

Methods

Data for this review were identified by searching MEDLINE with the search terms “multiple sclerosis” and “tremor”. References were also identified from relevant articles published between January 1966 and May 2012.

Results

The predominant type of MS tremor is a large-amplitude, postural, and kinetic tremor, which most commonly affects the arms, although tremor can also involve head, neck, vocal cords, and trunk. Involvement of the tongue, jaw, or palate has not been reported. Although the anatomical basis underlying tremor in MS is poorly understood, the link between the cerebellum and the MS-related tremor is supported by clinical and experimental studies. Currently available medication is often unsuccessful in most cases. Surgical treatment can be a satisfactory alternative to treat severe and disabling tremor.

Discussion

Tremor in MS patients could be considered as an advanced consequence of the disease and its presence suggests a more aggressive course. MS tremor can be severe and very disabling for a small group of patients. Treatment of MS tremor remains a great challenge. Recent studies suggest that dissociating tremor from cerebellar dysfunction using selected clinical tests would be the key issue to successful surgical treatment. Understanding the pathophysiology and biochemistry of tremor production in MS may lead to new therapeutic approaches.

Symptomatic therapy in multiple sclerosis: a review for a multimodal approach in clinical practice

As more investigations into factors affecting the quality of life of patients with multiple sclerosis (MS) are undertaken, it is becoming increasingly apparent that certain comorbidities and associated symptoms commonly found in these patients differ in incidence, pathophysiology and other factors compared with the general population. Many of these MS-related symptoms are frequently ignored in assessments of disease status and are often not considered to be associated with the disease. Research into how such comorbidities and symptoms can be diagnosed and treated within the MS population is lacking. This information gap adds further complexity to disease management and represents an unmet need in MS, particularly as early recognition and treatment of these conditions can improve patient outcomes. In this manuscript, we sought to review the literature on the comorbidities and symptoms of MS and to summarize the evidence for treatments that have been or may be used to alleviate them.

An Overview of Surgical Therapy for Movement Disorders

Surgical treatments are an important consideration in the management of many movement disorders, particularly for patients refractory to medications. Increasing number of published reports have demonstrated an overall improvement in motor function, activities of daily living and quality of life particularly with deep brain stimulation. In addition the procedure is also relatively safe. In this article, we review the various types of movement disorders that may benefit from surgical intervention.

Thalamic stimulation in multiple sclerosis: evidence for a ‘demyelinative thalamotomy’

The mechanism of action of deep brain stimulation (DBS) in the alleviation of tremor in multiple sclerosis (MS) and other neurological disorders is unknown. Moreover, whether the trauma accompanying this surgery is responsible for the induction of new MS plaques is controversial. Here we report the first description of the post-mortem imaging and pathologic findings in the brain of a MS patient who underwent thalamic DBS for the treatment of MS-induced tremor. MR imaging of formalin-fixed brain slices was carried out at 1.5, 3 and 7 Tesla and correlated with the histopathology. There were numerous demyelinative plaques in the white mater, cortex and deep gray matter. There were no plaques along the DBS tract within the sections that sampled the deep hemispheric white matter. However, deep within the thalamus focal demyelination approximated the tract, particularly in the region corresponding to the electrical field. The findings in this single case raise the possibility that focal demyelination may be induced by the electrical field and this may be responsible for long-lasting alleviation of tremor in the absence of continued electrostimulation.

Stereotactic neurosurgery for disabling tremor in multiple sclerosis: thalamotomy or deep brain stimulation?

Disabling tremor is common in multiple sclerosis and up to 75% of patients experience tremor at some point during their disease. The treatment of this tremor, however, remains challenging. Pharmacotherapy in general has been disappointing and stereotactic neurosurgery is becoming increasingly popular. However, the results of stereotactic treatments reported are variable and no systematic review has been performed. The aim of this study was to assess the role of thalamotomy and deep brain stimulation in the treatment of tremor in multiple sclerosis, and to compare the differences in efficacy and safety between the two techniques. We identified the relevant published studies and cases by searching the MEDLINE, EMBASS and the references lists of related articles, and performed a systematic review and assessment of the full texts of all articles selected. Initial tremor suppression was seen in 93.8% of patients who had thalamotomy and 96% in those who had deep brain stimulation. A total of 63.5% of patients had persistent tremor suppression at 12 months or more after thalamotomy. Twelve results for deep brain stimulation were not available in the reviewed literature. Functional improvement was seen only in 47.8% of those who underwent thalamotomy as opposed to 85.2% of those who had deep brain stimulation. While three of the four reported deaths were in patients who underwent thalamotomy, three of the four procedure-related haemorrhages followed DBS. Other common adverse effects like hemiparesis, dysarthria, swallowing difficulties, balance disorder, etc., was reported in both procedures. Numerous studies have attempted to assess the efficacy and safety of thalamotomy and DBS in the treatment of MS tremor, but no standardized outcome measures were used. Nonetheless, the data suggest that both thalamotomy and thalamic DBS are comparable procedures for tremor suppression and that adverse effects can occur with both procedures.

Deep brain stimulation and tremor

Deep brain stimulation (DBS) has been used to treat various tremor disorders for several decades. Medication-resistant, disabling essential tremor (ET) is the most common tremor disorder treated with DBS. The treatment has been consistently reported to result in significant benefit in upper extremity, as well as head and voice tremor, all of which were improved more dramatically with bilateral procedures. These benefits have been demonstrated to be sustained for up to 7 years. DBS has also been shown to be beneficial for the tremor associated with multiple sclerosis and post-traumatic tremor; however, fewer cases have been reported and the benefit is less consistent, less dramatic, and more transient than that seen with ET. The ventral intermediate nucleus of the thalamus is the most common DBS target for tremor disorders, but more recent studies have demonstrated benefits in tremor from DBS of the subthalamic area, primarily the zona incerta. Surgical complications are relatively uncommon and are generally less frequent than those seen with thalamotomy. Stimulation-related effects are usually mild and resolve with adjustment of stimulation parameters. DBS is thus a relatively safe and effective treatment for tremor disorders, particularly for medication-resistant, disabling ET, but may also have some role in medication-resistant, disabling tremor associated with multiple sclerosis and traumatic head injury.

Gamma knife thalamotomy for multiple sclerosis tremor

BACKGROUND

Some patients with MS suffer from disabling tremor. Improvement with medical treatment is modest, at best. Stereotactic surgery targeting the vim nucleus of the thalamus has been successful in alleviating MS tremor. Gamma knife radiosurgery represents a minimally invasive alternative to radiofrequency lesioning and DBS that can provide improvement in patients suffering from essential and parkinsonian tremor. We reviewed our experience with GK thalamotomy in the management of six consecutive patients suffering from disabling MS tremor.

METHODS

The median age at the time of radiosurgery was 46 years (range, 31 to 57 years). Intention tremor had been present for a median of three years (range 8 months to 12 years). One 4-mm isocenter was used to deliver a median maximum dose of 140 Gy (range, 130-150 Gy) to the vim nucleus of the thalamus opposite the side of the most disabling tremor. Clinical outcome was assessed using the Fahn-Tolosa-Marin scale.

RESULTS

The median follow-up was 27.5 months (range, 5-46 months). All patients experienced improvement in tremor after a median latency period of 2.5 months. More improvement was noted in tremor amplitude than in writing and drawing ability. In four patients, the tremor reduction led to functional improvement. One patient suffered from transient contralateral hemiparesis, which resolved after brief corticosteroid administration. No other complication was seen.

CONCLUSION

Gamma knife radiosurgical thalamotomy is effective as a minimally invasive alternative to stereotactic surgery for the palliative treatment of disabling MS tremor.

Kinematic analysis of thalamic versus subthalamic neurostimulation in postural and intention tremor

Deep brain stimulation of the thalamus (thalamic DBS) is an established therapy for medically intractable essential tremor and tremor caused by multiple sclerosis. In both disorders, motor disability results from complex interaction between kinetic tremor and accompanying ataxia with voluntary movements. In clinical studies, the efficacy of thalamic DBS has been thoroughly assessed. However, the optimal anatomical target structure for neurostimulation is still debated and has never been analysed in conjunction with objective measurements of the different aspects of motor impairment. In 10 essential tremor and 11 multiple sclerosis patients, we analysed the effect of thalamic DBS through each contact of the quadripolar electrode on the contralateral tremor rating scale, accelerometry and kinematic measures of reach-to-grasp-movements. These measures were correlated with the anatomical position of the stimulating electrode in stereotactic space and in relation to nuclear boundaries derived from intraoperative microrecording. We found a significant impact of the stereotactic z-coordinate of stimulation contacts on the TRS, accelerometry total power and spatial deviation in the deceleration and target period of reach-to-grasp-movements. Most effective contacts clustered within the subthalamic area (STA) covering the posterior Zona incerta and prelemniscal radiation. Stimulation within this region led to a mean reduction of the lateralized tremor rating scale by 15.8 points which was significantly superior to stimulation within the thalamus (P < 0.05, student's t-test). STA stimulation resulted in reduction of the accelerometry total power by 99%, whereas stimulation at the ventral thalamic border (68%) or within the thalamus proper (2.5%) was significantly less effective (P < 0.01). Concomitantly, STA stimulation led to a significantly higher increase of tremor frequency and decrease in EMG synchronization compared to stimulation within the thalamus proper (P < 0.001). In reach-to-grasp movements, STA stimulation reduced the spatial variability of the movement path in the deceleration period by 28.9% and in the target period by 58.4%, whereas stimulation within the thalamus was again significantly less effective (P < 0.05), with a reduction in the deceleration period between 6.5 and 21.8% and in the target period between 1.2 and 11.3%. An analysis of the nuclear boundaries from intraoperative microrecording confirmed the anatomical impression that most effective electrodes were located within the STA. Our data demonstrate a profound effect of deep brain stimulation of the thalamic region on tremor and ataxia in essential tremor and tremor caused by multiple sclerosis. The better efficacy of stimulation within the STA compared to thalamus proper favours the concept of a modulation of cerebello-thalamic projections underlying the improvement of these symptoms.

Post-deep brain stimulation — gradual non-stimulation dependent decrease in strength with attenuation of multiple sclerosis tremor

Tremor in multiple sclerosis is considered to be a persistent and progressive sign. We describe five patients with multiple sclerosis in whom upper limb tremor severity gradually decreased over a period of several years after deep brain stimulation. In every case this attenuation of tremor was accompanied by increasing pyramidal weakness in the relevant upper limb. In two patients this attenuation of tremor remained after stimulation was permanently switched off. In one other patient, where upper limb strength remained normal, tremor severity gradually worsened in spite of continuing stimulation. There was a highly significant difference (p = 0.0007) between the changes in intention tremor severities when the arms with increasing pyramidal weakness (n = 9) were compared to those in which normal strength was retained throughout follow-up period (n = 3); intention tremor decreased in the former and increased in the latter by means of -3.66 and +4.0 points of a 0-10 tremor scale respectively. There was also a significant correlation (0.699; p = 0.0359) between decreasing upper limb strength and decreasing intention tremor severity for the upper limbs of patients that had undergone contralateral DBS.

Tremor in multiple sclerosis

Tremor is estimated to occur in about 25 to 60 percent of patients with multiple sclerosis (MS). This symptom, which can be severely disabling and embarrassing for patients, is difficult to manage. Isoniazid in high doses, carbamazepine, propranolol and gluthetimide have been reported to provide some relief, but published evidence of effectiveness is very limited. Most trials were of small size and of short duration. Cannabinoids appear ineffective. Tremor reduction can be obtained with stereotactic thalamotomy or thalamic stimulation. However, the studies were small and information on long-term functional outcome is scarce. Physiotherapy, tremor reducing orthoses, and limb cooling can achieve some functional improvement. Tremor in MS remains a significant challenge and unmet need, requiring further basic and clinical research.

Multiple target deep brain stimulation for multiple sclerosis related and poststroke Holmes' tremor

BACKGROUND

The results from thalamic deep brain stimulation (DBS) for atypical tremor syndromes including tremor from multiple sclerosis (MS) and stroke are often disappointing. Three recent case reports have suggested that simultaneous stimulation of multiple thalamic targets can result in sustained improvement in such cases.

METHODS

We analyzed the effectiveness of multiple target DBS in one patient with MS-related tremor and another with poststroke Holmes' tremor.

RESULTS

In the patient with MS tremor, we implanted bilateral ventralis intermedius (V.im.) and ventralis oralis anterior (V.o.a.) thalamic electrodes; this patient had significant tremor improvement with stimulation of either V.im. or V.o.a. targets; however, we did not observe additive effects with simultaneous stimulation. In our patient with a poststroke Holmes' tremor, we implanted DBS electrodes in unilateral V.im., V.o.a., and the globus pallidus internus (Gpi); this patient had moderate tremor reduction with Gpi stimulation alone; neither V.im. nor V.o.a. stimulation provided additional benefit.

CONCLUSION

In one patient with MS tremor, simultaneous V.im. and V.o.a. stimulation was not superior to V.im. or V.o.a. stimulation alone. In one case of Holmes' tremor, Gpi stimulation was a useful alternative to thalamic stimulation.

Deep brain stimulation for neurologic and neuropsychiatric disorders

In the 1960s, ablative stereotactic surgery was employed for a variety of movement disorders and psychiatric conditions. Although largely abandoned in the 1970s because of highly effective drugs, such as levodopa for Parkinson's disease (PD), and a reaction against psychosurgery, the field has undergone a virtual renaissance, guided by a better understanding of brain circuitry and the circuit abnormalities underlying movement disorders such as PD and neuropsychiatric conditions, such as obsessive compulsive disorder. High-frequency electrical deep brain stimulation (DBS) of specific targets, introduced in the early 1990s for tremor, has gained widespread acceptance because of its less invasive, reversible, and adjustable features and is now utilized for an increasing number of brain disorders. This review summarizes the rationale behind DBS and the use of this technique for a variety of movement disorders and neuropsychiatric diseases.

Spiral drawing performance as an indicator of fine motor function in people with multiple sclerosis

This study investigated spiral drawing performance as an indicator of fine motor function, as well as to gain insight into adaptive movement strategies used by people with multiple sclerosis (MS). Seven people with MS, nine younger controls (mean age of 20) and eight older controls (mean age of 40) drew spirals on a graphics tablet at a comfortable speed and size. Spirography (i.e., a subjective visual assessment of the static trace) revealed indications of reduced control of the pen for people with MS. Analysis of the movements showed that people with MS tended to draw the spirals slower and with less pen pressure than controls. All groups increased their speed and pressure along with spiral size, but this increase was much steeper for the controls. MS participants drew spirals with more variability around an ideal trajectory, highlighting fine motor control degradation. MS patients tended to use a smaller scaling ratio, resulting in smaller spirals for a given number of revolutions. The younger and older control groups drew the spirals in a similar manner, and age was not a significant factor in any of the analyses. It is argued that the relatively lower pressure used, and slower, smaller movements (particularly during the more difficult outer sections of the spiral) are in part an adaptive strategy used to reduce movement variability. These results demonstrate the utility of the analysis of spiral movements as an objective technique for assessing motor control degradation, which can compliment the subjective rating based on the static pen trace. As such, it can provide further insight into the biomechanical strategies used when performing fine movements.

Symptomatic treatment of multiple sclerosis. Multiple Sclerosis Therapy Consensus Group (MSTCG) of the German Multiple Sclerosis Society

Besides immunomodulation and immunosuppression, the specific treatment of symptoms is an essential component of the overall management of multiple sclerosis (MS). Symptomatic treatment is aimed at the elimination or reduction of symptoms impairing the functional abilities and quality of life of the affected patients. Moreover, with symptomatic treatment the development of a secondary physical impairment due to an existing one may be avoided. Many therapeutic techniques as well as different drugs are used for the treatment of MS symptoms, but only a few of them have been investigated, especially in MS patients, and are approved by the national health authorities. Despite an overwhelming number of publications, only a few evidence-based studies exist and consensus reports are very rare, too. Therefore, it seemed necessary to develop a consensus statement on symptomatic treatment of MS comprising existing evidence-based literature as well as therapeutic experience of neurologists who have dealt with these problems over a long time. This consensus paper contains proposals for the treatment of the most common MS symptoms: disorders of motor function and coordination, of cranial nerve function, of autonomic, cognitive, and psychological functions as well as MS-related pain syndromes and epileptic seizures.

Neurosurgical treatment of multiple sclerosis

OBJECTIVES

To describe the role of neurosurgical techniques in treatment of symptoms of multiple sclerosis (MS).

METHODS

A review of the existing world literature searching (using PubMed, August 22, 2005) for key words 'multiple sclerosis' and multiple symptoms associated with MS including trigeminal neuralgia, pain (pump and rhizotomy), spasticity, intrathecal pump, hydrocephalus and stimulation (brain and spinal).

RESULTS

In total, 1,404 articles met selection criteria. These were narrowed based upon uniqueness of technique described, nature of information provided and avoidance of redundancy. Further, the methods listed were classified into groups of cranial and spinal techniques. Indications, brief description of technique and outcome/side effects were noted for each technique.

DISCUSSION

A vast, growing body of literature exists for various neurosurgical applications for MS treatment. Older techniques such as rhizolysis for neuralgia and rhizotomy for spasticity have been modified using stereotactic radiosurgery and deep brain stimulation, along with central nervous system stimulation and intrathecal pumps. Other applications continue to be found with varying degrees of success.

CONCLUSIONS

Neurosurgical techniques, based upon proper selection criteria, can significantly improve MS-related symptoms with low procedure-associated risk and therefore can substantially improve patients' quality of life.

Differential diagnosis of common tremor syndromes

Tremor is one of the most common involuntary movement disorders seen in clinical practice. In addition to the detailed history, the differential diagnosis is mainly clinical based on the distinction at rest, postural and intention, activation condition, frequency, and topographical distribution. The causes of tremor are heterogeneous and it can present alone (for example, essential tremor) or as a part of a neurological syndrome (for example, multiple sclerosis). Essential tremor and the tremor of Parkinson's disease are the most common tremors encountered in clinical practice. This article focuses on a practical approach to these different forms of tremor and how to distinguish them clinically. Evidence supporting various strategies used in the differentiation is then presented, followed by a review of formal guidelines or recommendations when they exist.

The effect of cystic cavities on deep brain stimulation in the basal ganglia: a simulation-based study

Although the therapeutic effect of deep brain stimulation (DBS) is well recognized, a fundamental understanding of the mechanisms responsible is still not known. In this study finite element method (FEM) modelling and simulation was used in order to study relative changes of the electrical field extension surrounding a monopolar DBS electrode positioned in grey matter. Due to the frequently appearing cystic cavities in the DBS-target globus pallidus internus, a nucleus of grey matter with and without a cerebrospinal fluid filled cystic cavity was modelled. The position, size and shape of the cyst were altered in relation to the electrode. The simulations demonstrated an electrical field around the active element with decreasing values in the radial direction. A stepwise change was present at the edge between grey and white matters. The cyst increased the radial extension and changed the shape of the electrical field substantially. The position, size and shape of the cyst were the main influencing factors. We suggest that cystic cavities in the DBS-target may result in closely related unexpected structures or neural fibre bundles being stimulated and could be one of the reasons for suboptimal clinical effects or stimulation-induced side effects.

Neuromodulation for movement disorders

The field of movement disorder surgery is expanding rapidly. This has been accompanied by improvements in neuromodulation technology and neuroimaging, in addition to a realisation that the medical and destructive neurosurgical methods previously employed do not provide an acceptable long-term benefit for many of these patients. The contemporary treatment of Parkinson's disease, dystonia, and other tremulous disorders using deep brain chronic electrical stimulation will be reviewed, and future directions discussed.