Analysis of action tremor and impaired control of movement velocity in multiple sclerosis during visually guided wrist-tracking tasks

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.

Efficacy of levetiracetam on upper limb movement in multiple sclerosis patients with cerebellar signs: a multicenter double-blind, placebo-controlled, crossover study

BACKGROUND AND PURPOSE

The literature provides contrasting results on the efficacy of levetiracetam (LEV) in multiple sclerosis (MS) patients with cerebellar signs. It was sought to evaluate the efficacy of LEV on upper limb movement in MS patients.

METHODS

In this multicenter double-blind placebo-controlled crossover study, MS patients with prevalently cerebellar signs were randomly allocated into two groups: LEV followed by placebo (group 1) or placebo followed by LEV (group 2). Clinical assessments were performed by a blinded physician at T0 (day 1), T1 (day 22), T2 (2-week wash-out period, day 35) and T3 (day 56). The primary outcome was dexterity in the arm with greater deficit, assessed by the nine-hole peg test (9HPT). Secondary clinical outcomes included responders on the 9HPT (∆9HPT >20%), tremor activity of the daily living questionnaire and self-defined upper limb impairment, through a numeric rating scale. Kinematic evaluation was performed using a digitizing tablet, providing data on normalized jerk, aiming error and centripetal acceleration.

RESULTS

Forty-eight subjects (45.2 ± 10.4 years) were randomly allocated into two groups (n = 24 each). 9HPT significantly improved in the LEV phase in both groups (P < 0.001). The LEV treatment phase led to a significant improvement (P < 0.01) of all clinical outcomes in group 1 and in dexterity in group 2. No significant changes were reported during both placebo phases in the two groups. Considering the kinematic analysis, only normalized jerk significantly improved after treatment with LEV (T0-T1) in group 1.

CONCLUSIONS

Levetiracetam treatment seems to be effective in improving upper limb dexterity in MS patients with cerebellar signs.

Functional neuroplasticity in response to cerebello-thalamic injury underpins the clinical presentation of tremor in multiple sclerosis

BACKGROUND

Tremor is present in almost half of multiple sclerosis (MS) patients. The lack of understanding of its pathophysiology is hampering progress in development of treatments.

OBJECTIVES

To clarify the structural and functional brain changes associated with the clinical phenotype of upper limb tremor in people with MS.

METHODS

Fifteen healthy controls (46.1 ± 15.4 years), 27 MS participants without tremor (46.7 ± 11.6 years) and 42 with tremor (46.6 ± 11.5 years) were included. Tremor was quantified using the Bain score (0-10) for overall severity, handwriting and Archimedes spiral drawing. Functional magnetic resonance imaging activations were compared between participants groups during performance of a joystick task designed to isolate tremulous movement. Inflammation and atrophy of cerebello-thalamo-cortical brain structures were quantified.

RESULTS

Tremor participants were found to have atrophy of the cerebellum and thalamus, and higher ipsilateral cerebellar lesion load compared to participants without tremor (p < 0.020). We found higher ipsilateral activation in the inferior parietal lobule, the premotor cortex and supplementary motor area in MS tremor participants compared to MS participants without tremor during the joystick task. Finally, stronger activation in those areas was associated with lower tremor severity.

CONCLUSION

Subcortical neurodegeneration and inflammation along the cerebello-thalamo-cortical and cortical functional neuroplasticity contribute to the severity of tremor in MS.

Upper Limb Intention Tremor in Multiple Sclerosis: An Evidence-Based Review of Assessment and Treatment

Background

To present the current knowledge on the characteristics, assessment, and treatment of upper limb intention tremor to inform and improve future intervention studies in patients with multiple sclerosis (MS), we conducted a literature review for articles on upper limb intention tremor in patients with MS.

Methods

Two reviewers conducted searches in PubMed, Web of Science, and MEDLINE (Ovid). Relevant articles, sorted on inclusion criteria, were examined for descriptions and assessments of upper limb intention tremor, and intervention studies were evaluated based on treatment type.

Results

Eight descriptive studies were found reporting on the incidence and severity of tremor, impairments, and lesion load. Ten studies focused on measurement of tremor using various assessments. Intervention studies included eight articles using a diverse set of noninvasive techniques mainly showing transient reduction in tremor amplitude and temporary increase in function. Eighteen studies on pharmacologic interventions were found, with most displaying positive outcomes and mediation of tremor; others showed little to no benefit. Surgical interventions included 17 studies on thalamotomy and 20 on deep brain stimulation. Most studies showed tremor improvement after surgery; however, most sample sizes were small, and interventions were highly invasive, with potential adverse effects resulting from surgery.

Conclusions

The literature on upper limb intention tremor in MS is relatively sparse. More studies are required to determine mechanism of action and to provide more suitable and sustainable interventions to decrease upper limb intention tremor and improve quality of life of individuals with MS.

The difference in visuomotor feedback velocity control during spiral drawing between Parkinson's disease and essential tremor

In a spiral task, the accuracy of the spiral trajectory, which is affected by tracing or tracking ability, differs between patients with Parkinson's disease (PD) and essential tremor (ET). However, not many studies have analyzed velocity differences between the groups during this task. This study aimed to examine differences between the groups related to this characteristic using a tablet. Fourteen PD, 12 ET, and 12 control group participants performed two tasks: tracing a given spiral (T1) and following a guiding point (T2). A digitized tablet was used to record movements and trajectory. Effects of direct visual feedback on intergroup and intragroup velocity were measured. Although PD patients had a significantly lower T1 velocity than the control group (p < 0.05), they could match the velocity of the guiding point (3.0 cm/s) in T2. There was no significant difference in the average T1 velocity between ET and the control groups (p = 0.26); however, the T2 velocity of ET patients was significantly higher than the control group (p < 0.05). They were also unable to adjust the velocity to match the guiding point, indicating that ET patients have a poorer ability to follow dynamic guidance. When both groups of patients have similar action tremor severity, their ability to follow dynamic guidance was still significantly different. Our study combined visual feedback with spiral drawing and demonstrated differences in the following-velocity distribution in PD and ET. This method may be used to distinguish the tremor presentation of both diseases, and thus, provide accurate diagnosis.

Effect of visual information on step-tracking movements in patients with intention tremor due to multiple sclerosis

The effect of visual information on step-tracking movements was studied in 18 patients with intention tremor due to multiple sclerosis (MS) and 15 healthy controls. Participants performed a slow wrist step-tracking task with stationary targets under five visual feedback conditions. The display of the target and movement cues was selectively withdrawn to examine the effects of visual information on intention tremor and movement accuracy.

Results showed that intentio n tremor was most pronounced when visual display of both target and movement cues was available. Withdrawing visual information of the limb movement reduced tremor more than withdrawing the visual display of the target cues. Both the patient and control group was less accurate when the display of limb movement was occluded. Patients, however, were more dependent on visual information of the limb movement for accurate motor performance than healthy controls.

When the visual display of the limb movement was partially occluded between or near to the targets, tremor decreased without deterioration of movement accuracy.

Hilbert-Huang transform based instrumental assessment of intention tremor in multiple sclerosis

OBJECTIVE

This paper describes a method to extract upper limb intention tremor from gyroscope data, through the Hilbert-Huang transform (HHT), a technique suitable for the study of nonlinear and non-stationary processes. The aims of the study were to: (i) evaluate the method's ability to discriminate between healthy controls and MS subjects; (ii) validate the proposed procedure against clinical tremor scores assigned using Fahn's tremor rating scale (FTRS); and (iii) compare the performance of the HHT-based method with that of linear band-pass filters.

APPROACH

HHT was applied on gyroscope data collected on 20 MS subjects and 13 healthy controls (CO) during finger-to-nose tests (FNTs) instrumented with an inertial sensor placed on the hand. The results were compared to those obtained after traditional linear filtering. The tremor amplitude was quantified with instrumental indexes (TIs) and clinical FTRS ratings.

MAIN RESULTS

The TIs computed after HHT-based filtering discriminated between CO and MS subjects with clinically-detected intention tremor (MS_T). In particular, TIs were significantly higher in the final part of the movement (TI2) with respect to the first part (TI1), and, for all components (X, Y, Z), MS_T showed a TI2 significantly higher than in CO subjects. Moreover, the HHT detected subtle alterations not visible from clinical ratings, as TI2 (Z-component) was significantly increased in MS subjects without clinically-detected tremor (MS_NT). The method's validity was demonstrated by significant correlations between clinical FTRS scores and TI2 related to X (rs = 0.587, p = 0.006) and Y (rs = 0.682, p < 0.001) components. Contrarily, fewer differences among the groups and no correlation between instrumental and clinical indexes emerged after traditional filtering.

SIGNIFICANCE

The present results supported the use of the HHT-based procedure for a fully-automated quantitative and objective measure of intention tremor in MS, which can overcome the limitations of clinical scales and provide supplementary information about this sign.

Intention tremor and deficits of sensory feedback control in multiple sclerosis: a pilot study

BACKGROUND

Intention tremor and dysmetria are leading causes of upper extremity disability in Multiple Sclerosis (MS). The development of effective therapies to reduce tremor and dysmetria is hampered by insufficient understanding of how the distributed, multi-focal lesions associated with MS impact sensorimotor control in the brain. Here we describe a systems-level approach to characterizing sensorimotor control and use this approach to examine how sensory and motor processes are differentially impacted by MS.

METHODS

Eight subjects with MS and eight age- and gender-matched healthy control subjects performed visually-guided flexion/extension tasks about the elbow to characterize a sensory feedback control model that includes three sensory feedback pathways (one for vision, another for proprioception and a third providing an internal prediction of the sensory consequences of action). The model allows us to characterize impairments in sensory feedback control that contributed to each MS subject's tremor.

RESULTS

Models derived from MS subject performance differed from those obtained for control subjects in two ways. First, subjects with MS exhibited markedly increased visual feedback delays, which were uncompensated by internal adaptive mechanisms; stabilization performance in individuals with the longest delays differed most from control subject performance. Second, subjects with MS exhibited misestimates of arm dynamics in a way that was correlated with tremor power. Subject-specific models accurately predicted kinematic performance in a reach and hold task for neurologically-intact control subjects while simulated performance of MS patients had shorter movement intervals and larger endpoint errors than actual subject responses. This difference between simulated and actual performance is consistent with a strategic compensatory trade-off of movement speed for endpoint accuracy.

CONCLUSIONS

Our results suggest that tremor and dysmetria may be caused by limitations in the brain's ability to adapt sensory feedback mechanisms to compensate for increases in visual information processing time, as well as by errors in compensatory adaptations of internal estimates of arm dynamics.

Interference of upper limb tremor on daily life activities in people with multiple sclerosis

SUMMARY The interference of upper limb intention tremor on activities of daily living was described in 32 persons with multiple sclerosis. Ratings about their degree of impairment and disability (Functional Systems, Expanded Disability Status Scale, Functional Independence Measure) was obtained from the multidisciplinary rehabilitation team. The individuals were interviewed using a questionnaire, mainly based on the items of the FIM scale, about the interference of tremor during activities of daily life. Intention tremor is rarely an isolated symptom. It is extremely disabling and was reported to interfere the most with activities of daily life such as eating, drinking, grooming and dressing. A variety of aids and strategies to compensate for specific disabilities were reported reflecting the important counseling role of the occupational therapist in assisting persons to cope more effectively with tremor.

Effects of low-frequency thalamic deep brain stimulation in essential tremor patients

BACKGROUND

Essential tremor (ET) patients may present with postural and/or intentional tremor. But despite high-frequency thalamic deep brain stimulation (DBS) effectively suppressing both, the emergence of intentional tremor has been attributed to a higher extent to cerebellar dysfunction. Therefore, we hypothesized thalamic 10 Hz-stimulation, which is known to worsen motor functions, having more impact on intentional tremor than on postural tremor.

METHODS

In sixteen ET-patients with bilateral thalamic-DBS, tremor rating scale (TRS) and ultrasound-based tremor-amplitude measurements were analyzed by sequentially applying three DBS-settings in a randomized order: i) low-frequency stimulation (LFS), ii) DBS being turned off (DBS-OFF) and iii) high-frequency stimulation (HFS). Repeated measures analyses of variance for TRS and for the quotients of tremor-amplitudes during DBS-OFF and LFS for intentional (q(int)) and postural tasks (q(post)) were calculated. Finally, electrode localization and the abovementioned quotients were put into relation by Pearson's correlation coefficient.

RESULTS

HFS reduced TRS significantly compared to DBS-OFF and LFS (ps<.001), while the latter two also differed significantly with TRS being the worst during LFS (p<.05). Additionally, intentional tremor-amplitude appeared to be strongly influenced by LFS than postural tremor-amplitude (p<.05). Furthermore, a lower placement of the electrodes caused worse intentional tremor-amplitude during LFS (r=.517, p>.05), while postural tremor-amplitude was unrelated to electrode localization (ps<.05).

CONCLUSIONS

During LFS in ET-patients, there is a more severe exacerbation of intentional tremor compared to postural tremor. Possibly, there are two different mechanisms responsible for both tremor entities, making more refined stimulation regimes feasible in the future.

Gain-of-function mutations in the K(ATP) channel (KCNJ11) impair coordinated hand-eye tracking

BACKGROUND

Gain-of-function mutations in the ATP-sensitive potassium channel can cause permanent neonatal diabetes mellitus (PNDM) or neonatal diabetes accompanied by a constellation of neurological symptoms (iDEND syndrome). Studies of a mouse model of iDEND syndrome revealed that cerebellar Purkinje cell electrical activity was impaired and that the mice exhibited poor motor coordination. In this study, we probed the hand-eye coordination of PNDM and iDEND patients using visual tracking tasks to see if poor motor coordination is also a feature of the human disease.

METHODS

Control participants (n = 14), patients with iDEND syndrome (n = 6 or 7), and patients with PNDM (n = 7) completed three computer-based tasks in which a moving target was tracked with a joystick-controlled cursor. Patients with PNDM and iDEND were being treated with sulphonylurea drugs at the time of testing.

RESULTS

No differences were seen between PNDM patients and controls. Patients with iDEND syndrome were significantly less accurate than controls in two of the three tasks. The greatest differences were seen when iDEND patients tracked blanked targets, i.e. when predictive tracking was required. In this task, iDEND patients incurred more discrepancy errors (p = 0.009) and more velocity errors (p= 0.009) than controls.

CONCLUSIONS

These results identify impaired hand-eye coordination as a new clinical feature of iDEND. The aetiology of this feature is likely to involve cerebellar dysfunction. The data further suggest that sulphonylurea doses that control the diabetes of these patients may be insufficient to fully correct their neurological symptoms.

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.

Visual and proprioceptive contributions to compensatory and pursuit tracking movements in humans

An ongoing debate in the field of motor control considers how the brain uses sensory information to guide the formation of motor commands to regulate movement accuracy. Recent research has shown that the brain may use visual and proprioceptive information differently for stabilization of limb posture (compensatory movements) and for controlling goal-directed limb trajectory (pursuit movements). Using a series of five experiments and linear systems identification techniques, we modeled and estimated the sensorimotor control parameters that characterize the human motor response to kinematic performance errors during continuous compensatory and pursuit tracking tasks. Our findings further support the idea that pursuit and compensatory movements of the limbs are differentially controlled.

[Case of multiple sclerosis with "yes-yes" type head tremor]

A 32-year-old woman, who had developed head tremor and paresthesia of the right upper limb for several months, was admitted to our hospital The diagnosis of multiple sclerosis was made because the serial MRI showed multiple lesions in both the cerebral white matter and the cervical cord. Oligoclonal IgG band was positive. Her symptoms were improved by intravenous methylprednisolone and an antiepileptic drug (MEPM 1 g/day and CZP 1 mg/day). The head tremor was the so-called "yes-yes" type which shakes back and forth. Although this type of tremor has been considered to be developed by the lesions in the cerebellum, our patient seemed to develop the tremor by cervical cord lesion. Further investigation is needed to confirm the association of the head tremor and the cervical lesions in MS.

Extraction of sources of tremor in hand movements of patients with movement disorders

This paper proposes an efficient method to acquire sources of tremor in patients with movement disorders based on blind source separation of convolutive mixtures. The extracted sources indicated neural activities that might be generated in the central nervous system. Four patients with essential tremor were tested in a set of movement tasks. Subjects wore a data glove that measured finger movements of the hand. The experimental data were then fed to a convolutive-mixture model, which revealed sources that imbibed in them the tremor frequency components of 2--8 Hz. Time--frequency analysis of these sources might be of potential help to clinicians to devise tasks that can manifest visible tremor from patients.

Intraoperative neurophysiological assessment of disabling symptoms in DBS surgery

INTRODUCTION

Neurophysiological assessment can provide quantitative measures for the selected motor signs that have been targeted for surgery and may be helpful in predicting the therapeutic effects of deep brain stimulation (DBS) on pathological tremor, motor performance, and rigidity.

OBJECTIVE

To present a survey and demonstrate the contribution of neurophysiological assessment of side effects and effects on disabling motor symptoms at various steps of DBS surgery, and to confirm its role for optimal target localization, as an adjuvant to anatomic imaging.

MATERIAL AND METHODS

The data result from 192 nuclei in 118 procedures on patients with Parkinson's disease (84), essential tremor (24), Hallenvorder Spatz dystonia (4), multiple sclerosis (4), and Holmes tremor (2). The intraoperative neurophysiological monitoring (IOM) protocol consists of semimicroelectrode recording (for subthalamic nuclei), whereas accelerotransducers and spectral analysis allow assessment of tremor, finger tapping (FT), diadochokinesis (DDK), and determination of the distance between DBS electrodes and internal capsule (IC). Rigidity is assessed by surface EMG recordings in combination with a goniometer.

RESULTS

The determination of the functional distance between the DBS electrode and the IC is based on the activation functions of axons in the IC. We show the high sensitivity of accelerometers for tremor over a large part of the body, the relationship between clinical scores and spectral frequencies of FT and DDK. Parkinsonian rigidity can be assessed from surface EMG (sEMG) by means of a balance coefficient, which can detect negative rigidity, for low unified Parkinson's disease rating scale (UPDRS) scores (0-2) and quantified EMG when negative rigidity is excluded.

CONCLUSION

Accelerometer and sEMG recording have shown their value for intraoperative assessment of disabling motor symptoms and side effects during surgery, to optimize the target position electrodes for DBS. The combination with contemporary signal analyzing techniques permit intraoperative monitoring without a significant delay. IONM improves sensitivity and adds objective neurophysiological data.

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.

Digitised spirography as an evaluation tool for intention tremor in multiple sclerosis

This study investigated validity and reliability of digitised circle and square spiral drawing for quantifying intention tremor severity and related disability in patients with multiple sclerosis (MS). The tremor amplitude was measured as the standard deviation of the drawing velocity of the arm in the radial and tangential direction for circle spiral drawing, and in the horizontal and vertical direction for square spiral drawing. Results were compared with those of MS patients without tremor and healthy controls, and correlated with clinical assessments of tremor severity and arm functionality including Fahn's tremor rating scale, Test d'Evaluation des Membres supérieurs des Personnes Agées (TEMPA) and the nine-hole-peg test to examine validity. Comparison of patient's performance between four repeated trials examined short-term test-retest reliability. All digitised spirography variables discriminated between the MS-tremor and both MS-no-tremor and healthy control groups. Validity was also shown by high spearman correlation coefficients between spirography variables and clinical ratings. Tremor appeared to be most profound in the radial and vertical direction during circle and square spiral drawing, respectively. The consistency and high correlations between four repeated executions indicated short-term test-retest reliability. We conclude that the digitised spirography provide a useful instrumentation for quantifying MS intention tremor.

Engineering better wheelchairs to enhance community participation

With about 2.2 million Americans currently using wheeled mobility devices, wheelchairs are frequently provided to people with impaired mobility to provide accessibility to the community. Individuals with spinal cord injuries, arthritis, balance disorders, and other conditions or diseases are typical users of wheelchairs. However, secondary injuries and wheelchair-related accidents are risks introduced by wheelchairs. Research is underway to advance wheelchair design to prevent or accommodate secondary injuries related to propulsion and transfer biomechanics, while improving safe, functional performance and accessibility to the community. This paper summarizes research and development underway aimed at enhancing safety and optimizing wheelchair design.

Online movement control in multiple sclerosis patients with tremor: effects of tendon vibration

Patients with intention tremor due to multiple sclerosis (MS) exhibit an increased reliance on visual feedback in the sensorimotor control of slow goal-directed movements. In the present study, the use of proprioceptive information was investigated in MS patients with intention tremor compared to MS patients without tremor and healthy controls. Tendon vibration was applied to the wrist extensor muscles during a memory-guided slow wrist step-tracking task to investigate the use of muscle spindle afferent information in online movement control. A significant reduction of movement amplitude was induced by tendon vibration in all three groups, but the effect was found to be smaller in MS patients with tremor (28%) than in subjects without tremor (50%). Vibration also induced an increase of overall tremor amplitude in the MS tremor group; however, its effect on movement amplitude was not directly related to (changes in) tremor severity. The results suggest that the decreased online use of proprioceptive information in MS patients with tremor reflects an adaptation over time to cope with a tremor-related noisy background. Abnormalities in proprioceptive processing may explain why MS patients with tremor show an increased reliance on visual feedback for online motor control.

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.

Neurophysiologic intervention in deep brain stimulation treatment for movement disorders: a practical framework

Clinical neurophysiology has always played an important interventional role throughout the perioperative stages in functional neurosurgery. On the one hand, some neurophysiologic procedures have become an integrated part of neurosurgery. On the other hand, in deep brain stimulation, although the surgical electrode implantation is an essential step, the therapeutic effects are actually produced by electrically modulating the physiologic activity of the brain. We review the topic of neurophysiologic intervention in the deep brain stimulation for movement disorders by presenting the evidence derived from our own experiences based on an integrated group located at two hospitals in London and Oxford, UK, and mainly covering tremor caused by multiple sclerosis, Parkinson's disease and dystonia.

The effect of changed visual feedback on intention tremor in multiple sclerosis

In patients with multiple sclerosis (MS), intention tremor amplitude is enhanced during the visually guided compared to the memory guided motor tasks. In the present study, the effect of visual feedback on intention tremor was investigated during visually guided wrist step-tracking tasks. Specifically, visual feedback of the hand was provided either instantly or averaged over different time windows. Thirteen MS patients with intention tremor and 14 healthy controls performed the wrist step-tracking task, while the visual representation of the actual hand position was displayed instantly or averaged over time windows of 150, 250 and 350 ms. It has been found in the patient group that, in association with a decreased initial error and decreased tremor amplitude on the screen, the amplitude of the actual performed tremor also decreased when visual feedback was changed. The tremor reduction was not different between conditions with manipulated feedback, although delays in presenting visual feedback of the hand position increased when the time window was larger. The reduction in overall tremor amplitude was unlikely related to other factors, such as eye fixation deficits or the speed of the primary hand movement. These results suggest that hand tremor severity is dependent on the visual feedback of position and movement errors.

The direction of oscillation in spiral drawings can be used to differentiate distal and proximal arm tremor

The assessment of the extent of involvement of the distal and proximal joints in a complex arm tremor is important clinically, as tremor generated around the distal and proximal arm joints can be differentially alleviated by surgical intervention to the thalamic and subthalamic targets, respectively. We observed that the tremor present in spiral drawings shows a diagonal directional preference. We hypothesized that the directional preference of tremor within spiral drawings could be related to the involvement of different arm joints. In this study, we tested this hypothesis by: (1) studying simulated tremulous drawings performed by healthy subjects with the joints selectively restrained; (2) recording surface EMGs from the forearm extensor and deltoid muscles during drawing; and (3) mathematical modelling the kinematics of the arm in 2D drawings. Our data showed that a "main diagonal" axis of orientation of the tremor along the orientation of the forearm indicates a predominantly proximal tremor driven by the shoulder, and a "cross diagonal" axis of orientation of tremor (i.e. perpendicular to the forearm) indicates that the tremor is predominantly distal and driven by the elbow or wrist. We conclude that the spiral drawing task can be used as an objective and quantitative method for differentiating the involvement of the proximal and distal arm joints in complex arm tremors.

Thalamotomy versus thalamic stimulation for multiple sclerosis tremor

Disabling intractable tremor occurs frequently in patients with multiple sclerosis (MS). There is currently no effective medical treatment available, and the results of surgical intervention have been variable. Thalamotomy has been the mainstay of neurosurgical therapy for intractable MS tremor, however the popularisation of deep brain stimulation (DBS) has led to the adoption of chronic thalamic stimulation in an attempt to ameliorate this condition. With the goal of examining the relative efficacy and adverse effects of these two surgical strategies, we studied twenty carefully selected patients with intractable MS tremor. Thalamotomy was performed in 10 patients, with chronic DBS administered to the remaining 10. Both thalamotomy and thalamic stimulation produced improvements in postural and intention tremor. The mean improvement in postural tremor at 16.2 months following surgery was 78%, compared with a 64% improvement after thalamic stimulation (14.6 month follow-up) (P > 0.05). Intention tremor improved by 72% in the group undergoing thalamotomy, a significantly larger gain than the 36% tremor reduction following DBS (P < 0.05). Early postoperative complications were common in both groups. Permanent complications related to surgery occurred in four patients overall. Following thalamotomy, long-term adverse effects were observed in three patients (30%), and comprised hemiparesis and seizures. Only one patient in the thalamic stimulation group experienced a permanent deficit (monoparesis). We conclude that thalamotomy is a more efficacious surgical treatment for intractable MS tremor, however the higher incidence of persistent neurological deficits in patients receiving lesional surgery may support the use of DBS as the preferred surgical strategy.

Quantifying drug-induced dyskinesias in the arms using digitised spiral-drawing tasks

In this study, we quantify the severity of drug-induced dyskinesias in the arms of Parkinson's disease (PD) patients using digitised spiral-drawing tasks. Two spiral drawings, namely a circular and a square spiral, are designed to, respectively, represent the continuous and discrete arm motions, and the size of the spiral is decided so that both the distal and proximal arm joints are involved. Fifteen PD patients, average disease duration 14.4+/-7.4 years, were assessed 30 min after a levodopa challenge whilst performing circular and square spiral-drawing tasks. The velocity of drawing movements was computed and the amplitude of the involuntary dyskinetic movements was measured as the standard deviation of the drawing velocity (SD-DV). The mean amplitude of dyskinetic movements was compared between arms and tasks and was correlated with clinical measures including the Bain dyskinesia scale and the total unified Parkinson's disease rating scale (UPDRS) score. The results showed that there was no statistically significant difference in the amplitude of dyskinesias either between the arms or between the continuous (circular) and discrete (square) spiral drawings in this group of PD patients, but interestingly the interaction between arm and drawing pattern was significant. Significant correlations were found between the magnitude of dyskinesia measured from the spiral-drawing tasks and both the 'on' or 'off' UPDRS and also the Bain dyskinesia scale. We conclude that the drawing tasks may be used to provide an objective method of quantifying the severity of drug-induced dyskinesias in the arm in PD patients.

Effects of peripheral cooling on intention tremor in multiple sclerosis

OBJECTIVE

To investigate the effect of peripheral sustained cooling on intention tremor in patients with multiple sclerosis (MS). MS induced upper limb intention tremor affects many functional activities and is extremely difficult to treat.Materials/

METHODS

Deep (18 degrees C) and moderate (25 degrees C) cooling interventions were applied for 15 minutes to 23 and 11 tremor arms of patients with MS, respectively. Deep and moderate cooling reduced skin temperature at the elbow by 13.5 degrees C and 7 degrees C, respectively. Evaluations of physiological variables, the finger tapping test, and a wrist step tracking task were performed before and up to 30 minutes after cooling.

RESULTS

The heart rate and the central body temperature remained unchanged throughout. Both cooling interventions reduced overall tremor amplitude and frequency proportional to cooling intensity. Tremor reduction persisted during the 30 minute post cooling evaluation period. Nerve conduction velocity was decreased after deep cooling, but this does not fully explain the reduction in tremor amplitude or the effects of moderate cooling. Cooling did not substantially hamper voluntary movement control required for accurate performance of the step tracking task. However, changes in the mechanical properties of muscles may have contributed to the tremor amplitude reduction.

CONCLUSIONS

Cooling induced tremor reduction is probably caused by a combination of decreased nerve conduction velocity, changed muscle properties, and reduced muscle spindle activity. Tremor reduction is thought to relate to decreased long loop stretch reflexes, because muscle spindle discharge is temperature dependent. These findings are clinically important because applying peripheral cooling might enable patients to perform functional activities more efficiently.

Interaction between eye and hand movements in multiple sclerosis patients with intention tremor

Deficient eye and hand movements are present in patients with multiple sclerosis. In the present study, eye and hand movements were simultaneously measured during visually guided wrist step-tracking tasks in 16 patients with intention tremor and 15 healthy controls. The coupling between eye and hand movements was analyzed during simultaneous eye-hand tracking, and interactions were studied by comparing the coordinated eye-hand condition with isolated eye- or hand-tracking conditions. Despite movement abnormalities, the onset of eye and hand movements was highly correlated and an invariant coupling between the saccadic completion time and hand peak velocity was found, suggesting that the temporal coupling was very much preserved. The differences between the experimental tracking conditions suggest that, in MS patients with intention tremor, the ocular system influenced the hand movements. Intention tremor amplitude was reduced when there was no preceding saccadic eye movement, whereas conversely, eye movements were not affected by different hand tremor severity.

Effects of vision and arm position on amplitude of arm postural tremor in patients with multiple sclerosis11No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit on the author(s) or on any organization with which the author(s) is/are associated

OBJECTIVES

To quantify the effects of vision and arm position on arm postural tremor, comparisons were made between flexed and extended arm positions performed with the eyes open and closed.

DESIGN

Case-control study.

SETTING

National multiple sclerosis (MS) center in Belgium.

PARTICIPANTS

Sixteen patients (32 arms) with MS who had intention tremor and 16 healthy controls (32 arms).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURE

The amplitude of postural tremor was assessed by a magnetic position sensor attached to the index finger.

RESULTS

The amplitude of postural tremor was not influenced by changes in visual condition or different arm positions. Both healthy controls and MS patients made more directional changes in the flexed, compared with the extended arm position.

CONCLUSIONS

The amplitude of the arm postural tremor in MS is independent of vision and arm position. Selecting 1 arm position is sufficient to assess postural tremor amplitude.

The neural substrates of driving at a safe distance: a functional MRI study

An important driving skill is the ability to maintain a safe distance from a preceding car. To determine the neural substrates of this skill we performed functional magnetic resonance imaging of simulated driving in 21 subjects. Subjects used a joystick to adjust their own driving speed in order to maintain a constant distance from a preceding car traveling at varying speeds. The task activated multiple brain regions. Activation of the cerebellum may reflect visual feedback during smooth tracking of the preceding car. Co-activation of the basal ganglia, thalamus and premotor cortex is related to movement selection. Activation of a premotor-parietal network is related to visuo-motor co-ordination. Task performance was negatively correlated with anterior cingulate activity, consistent with the role of this region in error detection and response selection.

On-line feedback control of human visually guided slow ramp tracking: effects of spatial separation of visual cues

Visual feedback control of tracking movements is dependent upon a visual comparison of the guiding target and moving limb positions but the human fovea greatly restricts the area of high acuity vision. The effect of vertically separating the target and movement cues in a slow movement task is investigated. Subjects track a slow constant velocity target in the horizontal plane with wrist flexion controlled cursor movements. The effects of changes in the vertical distance between the two cues upon tracking performance were observed. When both cursors were at the same level, tracking was most accurate but showed significant intermittency around 2 Hz in frequency. Increased separation of cues reduced significantly both accuracy and intermittency; tracking was smoother but less accurate. Thus, feedback control is dependent upon the efficiency of positional comparison and hence becomes less effective as the cue separation increases. These results also support previous studies suggesting each cue makes an equal contribution to visuomotor feedback control, each acting as a reference to the other.

Neuronal activity related to the visual representation of arm movements in the lateral cerebellar cortex

Testing the hypothesis that the lateral cerebellum forms a sensory representation of arm movements, we investigated cortical neuronal activity in two monkeys performing visually guided step-tracking movements with a manipulandum. A virtual target and cursor image were viewed co-planar with the manipulandum. In the normal task, manipulandum and cursor moved in the same direction; in the mirror task, the cursor was left-right reversed. In one monkey, 70- and 200-ms time delays were introduced on cursor movement. Significant task-related activity was recorded in 31 cells in one animal and 142 cells in the second: 10.2% increased activity before arm movements onset, 77.1% during arm movement, and 12.7% after the new position was reached. To test for neural representation of the visual outcome of movement, firing rate modulation was compared in normal and mirror step-tracking. Most task-related neurons (68%) showed no significant directional modulation. Of 70 directionally sensitive cells, almost one-half (n = 34, 48%) modulated firing with a consistent cursor movement direction, many fewer responding to the manipulandum direction (n = 9, 13%). For those "cursor-related" cells tested with delayed cursor movement, increased activity onset was time-locked to arm movement and not cursor movement, but activation duration was extended by an amount similar to the applied delay. Hence, activity returned to baseline about when the delayed cursor reached the target. We conclude that many cells in the lateral cerebellar cortex signaled the direction of cursor movement during active step-tracking. Such a predictive representation of the arm movement could be used in the guidance of visuo-motor actions.

Intention tremor during manual aiming: a study of eye and hand movements

Accurate goal-directed movements toward a visual target require a precise coordination of both the oculomotor and limb motor systems. Intention tremor and eye movement deficits are frequently observed in multiple sclerosis (MS). The goal of this study was to examine the characteristics of intention tremor and simultaneously produced eye movements during rapid goal-directed movements. Eye and hand movements were synchronously measured in 16 MS patients with intention tremor and 16 control subjects. Manual performances of the patient group were characterized by a delayed onset, slower execution and aiming inaccuracies. In line with the clinically defined picture of intention tremor differences between patients and control subjects were most pronounced toward the end of the movement. Dependent variables were obviously greater in MS patients compared with control subjects, and correlated well with clinical outcome measures. The application of an inertial load to the limb did not show any effect on intention tremor. In addition to impaired limb coordination, evidence has been found that eye movements, too, were abnormal in patients compared with control subjects. Moreover, eye and hand movement deficits seemed to be closely related, suggesting a common underlying command structure. Inaccurate eye movements were likely to hamper an accurate motor performance of the hand.

Increased response to visual feedback of drug-induced dyskinetic movements in advanced Parkinson's disease

To investigate the response to visual feedback of involuntary movements which have a frequency composition similar to cerebellar tremor but are not caused by cerebellar damage, we have tested six advanced Parkinson's disease (PD) patients with drug-induced dyskinetic movements using visually guided wrist tracking tasks. Tracking performance was assessed under three visual conditions: (1) both guiding target and movement cursor were displayed continuously; (2) the target display was turned off for the second half of each trial; or (3) the cursor display, but not the target, was turned off for the second half of each trial. The response to visual feedback of drug-induced dyskinetic movements at 1-5 Hz in these advanced PD patients were significantly increased than in normal controls. This suggests that increased response to visual feedback might be a common feature of low frequency involuntary movements and not directly caused by cerebellar damages.

Dissociation of 'on-line' and 'off-line' visuomotor control of the arm by focal lesions in the cerebellum and brainstem

Visuomotor control of the arm was assessed in a single case study of a subject with focal lesions in the cerebellum and brainstem. A dissociation between 'on-line' and 'off-line' visuomotor control was revealed: impairments in 'on-line' visuomotor control included inaccuracy of tracking velocity, increase in spatial pointing variability and a delay in simple reaction time; whereas the patient was able to adapt to a gain change in 'off-line' visual feedback during a pointing task, and his adaptation was less affected than that of control subjects by trial-to-trial random fluctuations in 'off-line' visual feedback. We conclude that focal damage in the cerebellar peduncles may be principally responsible for this dissociation.

Distal versus proximal arm tremor in multiple sclerosis assessed by visually guided tracking tasks

OBJECTIVES

To compare action tremor (AT) during manual tracking in normal subjects and patients with multiple sclerosis with tremor (MS-tremor group) and without tremor (MS-no tremor group), and to differentiate tremor occurring predominantly around the distal joint from that involving the proximal joints of the arm.

METHODS

Subjects performed both a visually guided ramp tracking task using wrist flexion/extension and a whole arm circle tracking task using shoulder movement. Action tremor at the wrist or shoulder was computed as the SD of the tracking velocity. The ratio of wrist:arm tremor was then calculated to differentiate distal from proximal tremor in the tested arm. Frequency spectra of the records were also examined.

RESULTS

During wrist tracking, AT in patients with multiple sclerosis contained a major frequency component at 4-5 Hz; the frequency was slightly lower during whole arm tracking. The ratio of wrist:arm tremor was significantly higher in the MS-tremor group. Of 12 tested arms, eight had tremor significantly weighted towards the distal joint, only one towards the proximal joint, and three had a ratio inside the control range.

CONCLUSIONS

AT in the arms of patients with multiple sclerosis can be effectively differentiated into proximal or distal using these two different tracking tasks. Despite the variability of the effects of multiple sclerosis, most of the AT was distal rather than proximal in this group of patients. Possibly conduction block along the corticocerebellocortical pathways caused this distal tremor.