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

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.

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.

Cued motor imagery in patients with multiple sclerosis

Motor imagery (MI) is a promising practice tool in neurorehabilitation. However, in patients with multiple sclerosis (MS), impairments in MI accuracy and temporal organization were found during clinical assessment, which may limit the benefits of MI practice. Therefore, we investigated whether the MI quality of MS patients could be optimized by means of external cueing. Fourteen patients with MS and 14 healthy control patients physically executed and visually imagined a goal-directed upper limb task in the presence and absence of added visual and auditory cues. MI quality was assessed by means of eye-movement registration. As main results, it was found that MS patients had significant higher eye-movement times than controls during both execution and imagery, and overestimated the to-be-imagined movement amplitude when no external information was provided during imagery. External cues, however, decreased patients' MI duration and increased the spatial accuracy of their imagined movements. In sum, our results indicate that MS patients imagine movements in a better way when they are provided with external cues during MI. These findings are important for developing rehabilitation strategies based on MI in patients with MS.

External cueing improves motor imagery quality in patients with Parkinson disease

BACKGROUND

Patients with Parkinson disease (PD) are often profoundly slow in their performance of physical tasks, as well as in motor imagery (MI). This may limit the implementation and potential benefits of MI practice during rehabilitation.

OBJECTIVE

The authors investigated whether the quality of MI could be improved by external cueing.

METHODS

Fourteen patients with PD and 14 healthy controls physically executed and visually imagined a goal-directed aiming task and a box-and-block task, both in the presence and absence of visual and auditory cues. Mental chronometry and eye movement recording allowed objective evaluation of the temporal and spatial characteristics of MI when compared with physical execution. Visual analogue scales were used to assess imagery vividness.

RESULTS

The presence of visual cues significantly reduced the patients' bradykinesia during MI and increased their imagery vividness.

CONCLUSIONS

Visual cueing optimizes MI quality for PD patients and is a potential tool to increase the efficacy of MI practice in PD rehabilitation.

Cerebellar ataxia: pathophysiology and rehabilitation

This series of articles for rehabilitation in practice aims to cover a knowledge element of the rehabilitation medicine curriculum. Nevertheless they are intended to be of interest to a multidisciplinary audience. The competency addressed in this article is 'The trainee consistently demonstrates a knowledge of management approaches for specific impairments including spasticity, ataxia.'

Effect of terminal accuracy requirements on temporal gaze-hand coordination during fast discrete and reciprocal pointings

Background

Rapid discrete goal-directed movements are characterized by a well known coordination pattern between the gaze and the hand displacements. The gaze always starts prior to the hand movement and reaches the target before hand velocity peak. Surprisingly, the effect of the target size on the temporal gaze-hand coordination has not been directly investigated. Moreover, goal-directed movements are often produced in a reciprocal rather than in a discrete manner. The objectives of this work were to assess the effect of the target size on temporal gaze-hand coordination during fast 1) discrete and 2) reciprocal pointings.

Methods

Subjects performed fast discrete (experiment 1) and reciprocal (experiment 2) pointings with an amplitude of 50 cm and four target diameters (7.6, 3.8, 1.9 and 0.95 cm) leading to indexes of difficulty (ID = log₂[2A/D]) of 3.7, 4.7, 5.7 and 6.7 bits. Gaze and hand displacements were synchronously recorded. Temporal gaze-hand coordination parameters were compared between experiments (discrete and reciprocal pointings) and IDs using analyses of variance (ANOVAs).

Results

Data showed that the magnitude of the gaze-hand lead pattern was much higher for discrete than for reciprocal pointings. Moreover, while it was constant for discrete pointings, it decreased systematically with an increasing ID for reciprocal pointings because of the longer duration of gaze anchoring on target.

Conclusion

Overall, the temporal gaze-hand coordination analysis revealed that even for high IDs, fast reciprocal pointings could not be considered as a concatenation of discrete units. Moreover, our data clearly illustrate the smooth adaptation of temporal gaze-hand coordination to terminal accuracy requirements during fast reciprocal pointings. It will be interesting for further researches to investigate if the methodology used in the experiment 2 allows assessing the effect of sensori-motor deficits on gaze-hand coordination.

Grip Force Control in Individuals With Multiple Sclerosis

Background. Appropriate regulation of grip force is essential in performance of various activities of daily living such as drinking, eating, buttoning a shirt, and so on. The extent to which individuals with multiple sclerosis (MS) are able to regulate grip forces while performing elements of the activities of daily living is largely unknown. Objective. To investigate how individuals with MS control grip force during performance of functional tasks. Methods. This study evaluated the grip force control in selected individuals with MS (n = 9) and healthy control subjects (n = 9) while they performed the task of lifting and placing an instrumented object on a shelf and the task of lifting the object and bringing it close to the mouth to mimic drinking. The grip forces, object acceleration, force ratio, and time lag were recorded and analyzed. Results. The individuals with MS used significantly larger peak grip force and force ratio than control subjects while performing both tasks and for both hands. In addition, the time lag between the peaks of grip and load forces was significantly longer in individuals with MS. Conclusion. The application of excessive grip force could predispose individuals with MS to additional fatigue and musculoskeletal overuse trauma. Rehabilitation protocols for the MS population may need to account for increased levels of grip force applied during the performance of functional tasks.

The effect of levetiracetam on tremor severity and functionality in patients with multiple sclerosis

BACKGROUND

Multiple sclerosis (MS) intention tremor is a disabling symptom, which is difficult to treat.

OBJECTIVES

To investigate the effects of levetiracetam, an antiepileptic drug, on tremor severity and related functionality in MS.

METHODS

A randomized, double-blind, placebo-controlled, cross-over study examined the effects of 6 weeks of oral levetiracetam administration (starting dose=250 mg/day, maximal dose=2000 mg/day) in 18 MS patients with disabling intention tremor. Primary outcome was Fahn's Tremor Rating Scale (FTRS) A&B. Secondary outcome measures were the nine-hole peg test, patient's opinion rated with the visual analog scale, FTRS C, and an activities of daily life questionnaire and validated tremor indexes derived during the performance of a digitized spiral drawing task and a wrist step-tracking task. Repeated measures analysis of variance and Friedman tests were applied.

RESULTS

In all, 14 patients completed the trial. Maximal dose intake ranged from 1000 to most commonly 2000 mg, depending on patients' tolerance level. No significant effects of levetiracetam were found for any outcome measure. Further analyses on subgroups with different tremor severity showed no differential effects. Eight patients reported adverse events such as fatigue and stomach ache.

CONCLUSIONS

Levetiracetam intake of 2000 mg/day did not affect tremor severity or functionality in patients with MS.

Hand function in multiple sclerosis: force coordination in manipulation tasks

OBJECTIVE

To evaluate the methodology for exploring the specific aspects of functional impairment in multiple sclerosis (MS) through the pattern of forces exerted in various manipulation tasks.

METHODS

Twelve mildly involved MS patients (EDSS 2.5-5.5) and 12 healthy controls performed various static and dynamic manipulation tasks with an instrumented device that recorded the grip (G; normal to the digit device contact area) and load force (L; tangential force that causes lifting).

RESULTS

MS patients consistently displayed lower indices of task performance (as assessed by the ability to produce the required L profiles) and force coordination (as assessed by G/L ratio, coupling of G and L, and G modulation) than the healthy controls across all tested tasks.

CONCLUSIONS

The applied methodology could be sensitive enough to detect the hand dysfunction in mildly involved individuals with MS. Particularly recommended for future evaluations of the impairment of hand function could be a simple lifting task and the static task of tracing a gradually changing L, as well as the variables depicting both the task performance and G/L ratio.

SIGNIFICANCE

The applied methodology could be developed into a standard clinical test for the assessment of hand function in MS and, possibly, in other neurological diseases.

Impaired object manipulation in mildly involved individuals with multiple sclerosis

We investigated hand function in mildly involved multiple sclerosis (MS) patients (N = 16; Expanded Disability Status Scale 1-5, 9-hole peg test 14-32 s) during static and dynamic manipulation tasks using an instrumented device. When compared with healthy controls (N = 16), the patients revealed impaired task performance regarding their ability to exert prescribed patterns of load force (L; force acting tangentially at the digits-object surface). Regarding the coordination of grip force (G; normal component) and L, the data only revealed an elevated G/L ratio, although both the G and L coupling (maximum correlation coefficients and the time lags between them) and the G modulation (gain and offset of G with respect to L) remained comparable in the two groups. Finally, most of the data suggested no MS-specific effects of switching from uni- to bimanual tasks, from available visual feedback to deprived feedback conditions. We conclude that the deterioration in the ability for precise control of external forces and overgripping could precede the decoupling of G and L and decreased G modulation in early phases of the disease. The results also suggest that the applied methodology could be sensitive enough to detect mild levels of impairment of hand function in MS and, possibly, other neurological diseases.

Adaptation of Voluntary Saccades, But Not of Reactive Saccades, Transfers to Hand Pointing Movements

Studying the transfer of visuomotor adaptation from a given effector (e.g., the eye) to another (e.g., the hand) allows us to question whether sensorimotor processes influenced by adaptation are common to both effector control systems and thus to address the level where adaptation takes place. Previous studies have shown only very weak transfer of the amplitude adaptation of reactive saccades—i.e., produced automatically in response to the sudden appearance of visual targets—to hand pointing movements. Here we compared the amplitude of hand pointing movements recorded before and after adaptation of either reactive or voluntary saccades, produced either in a saccade sequence task or in a single saccade task. No transfer to hand pointing movements was found after adaptation of reactive saccades. In contrast, a substantial transfer to the hand was obtained following adaptation of voluntary saccades produced in sequence. Large amounts of transfer between the two saccade types were also found. These results demonstrate that the visuomotor processes influenced by saccadic adaptation depend on the type of saccades and that, in the case of voluntary saccades, they are shared by hand pointing movements. Implications for the neurophysiological substrates of the adaptation of reactive and voluntary saccades are discussed.

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.

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.

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.

Relationship between multiple sclerosis intention tremor severity and lesion load in the brainstem

Intention tremor due to multiple sclerosis is clinically similar to cerebellar tremor. This study investigated, in 14 multiple sclerosis patients, the relationship between intention tremor severity and the lesion load in different infratentorial regions. Tremor amplitude was quantified during step-tracking tasks. The lesion load was measured on magnetic resonance images using an automated segmentation method. Intention tremor amplitude was significantly related to lesion load in the brainstem but not in the cerebellum. Specifically, tremor amplitude correlated with the lesion load in the contralateral pons, and patients with more severe tremor in both arms had a greater lesion load bilaterally in the pons. These results support the view that multiple sclerosis intention tremor is related to dysfunction of cerebellar inflow and/or outflow pathways.