Role of peripheral inputs in cerebellar tremor

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.

Is MS Intention Tremor Amplitude Related to Changed Peripheral Reflexes?

Intention tremor is related to lesions in the cerebellum or connected pathways. Intention tremor amplitude decreased after peripheral arm cooling in patients with multiple sclerosis (MS), likely caused by a reduction of muscle spindle afferent inflow, while amplitude increased when muscle spindles were artificially stimulated by tendon vibration. This study investigated the contribution of peripheral reflexes to the generation of MS intention tremor. Tendon reflexes of biceps, triceps, and brachioradialis, muscles were measured, using an electromechanical triggered reflex hammer. MS patients with (n = 17) and without (n = 17) upper limb intention and 18 healthy controls were tested. Latency of brachioradialis, biceps, and triceps tendon reflexes was greater in MS patients with tremor than in healthy controls and MS patients without tremor (except for the triceps reflex). Peak and peak-to-peak amplitude were not different between groups. It is concluded that tendon reflexes were delayed but not enlarged in MS patients with tremor.

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.'

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.

Delayed onset mixed involuntary movements after thalamic stroke: clinical, radiological and pathophysiological findings

Although occurrence of involuntary movements after thalamic stroke has occasionally been reported, studies using a sufficiently large number of patients and a control population are not available. Between 1995 and 1999, the author prospectively identified 35 patients with post-thalamic stroke delayed-onset involuntary movements, which included all or some degree of dystonia-athetosis-chorea-action tremor, occasionally associated with jerky, myoclonic components. A control group included 58 patients examined by the author during the same period who had lateral thalamic stroke but no involuntary movements. Demography, clinical features and imaging study results were compared. There were no differences in gender, age, risk factors, side of the lesion and follow-up periods. During the acute stage of stroke, the patients who had involuntary movements significantly more often had severe (< or = III/V) hemiparesis (50 versus 20%, P < 0.05) and severe sensory loss (in all modalities, P < 0.01) than the control group. At the time of assessment of involuntary movements, the patients with involuntary movements significantly more often had severe sensory deficit (in all modalities, P < 0.01) and severe limb ataxia (60 versus 5%, P < 0.01) than the control patients, but neither more severe motor dysfunction (7 versus 0%) nor more painful sensory symptoms (57 versus 57%). The patients with involuntary movements had a higher frequency of haemorrhagic (versus ischaemic) stroke (63 versus 31%, P < 0.05). Further analysis showed that dystonia-athetosis-chorea was closely associated with position sensory loss, whereas the tremor/myoclonic movements were related to cerebellar ataxia. Recovery of severe limb weakness seemed to augment the instability of the involuntary movements. Persistent failure of the proprioceptive sensory and cerebellar inputs in addition to successful, but unbalanced, recovery of the motor dysfunction seemed to result in a pathological motor integrative system and consequent involuntary movements in patients with relatively severe lateral-posterior thalamic strokes simultaneously damaging the lemniscal sensory pathway, the cerebellar-rubrothalamic tract and, relatively less severely, the pyramidal tract.

Influence of visual and proprioceptive afferences on upper limb ataxia in patients with multiple sclerosis

Our objective was to investigate how cooling of the arm and vision influence pointing movements in healthy subjects and patients with cerebellar limb ataxia due to clinically proven multiple sclerosis. An infrared video motion analysis system was used to record the unrestricted, horizontal pointing movements toward a target under three different conditions involving a moving, stationary, or imaginary target; a visual, or acoustic trigger; and vision or memory guidance. All three tasks were performed before and after cooling the arm in ice water. Patients had more hypermetric and slower pointing movements than controls under all tested conditions. Patients also had significantly larger three-dimensional finger sway paths during the postural phase and larger movement angles of the wrist joint. Memory-guided movements were the most hypermetric recorded in both groups. Cooling of the limb had no effect on amplitude or peak velocity of the pointing movement in either group under all tested conditions, but significantly reduced the three-dimensional finger sway path during the postural phase in patients with limb ataxia. Cooling-induced reduction of the finger sway was largest in those patients with the largest finger sway before cooling. In conclusion, the cooling-induced reduction of the proprioceptive afferent inflow, most probably of group I spindle afferents, reduces postural tremor of patients with cerebellar dysfunction.

Load compensation tasks evoke tremor in cerebellar patients: the possible role of long latency stretch reflexes

'Tremor' is one of the clinical signs of cerebellar dysfunction. Its nature remains subject to debate, one hypothesis being that of a predominant role of peripheral afferences in its genesis. This study was designed to study whether load compensating tasks, evoking sudden stretch, and thus stimulation of peripheral afferences induced tremor in cerebellar patients. We study the kinematics and EMG pattern of a load compensating task which consists of maintaining a constant elbow position despite the onset and cessation of a 2 Nm torque loading the elbow flexors in eight cerebellar patients and six controls. Angular position and velocity, and EMG of the biceps and triceps are recorded at a sampling rate of 1 kHz. In normal subjects, trajectories are simple with little overshoot of the aimed position. EMG analysis shows a long latency stretch response (LLSR) which initiates a phasic and then tonic voluntary activity. In cerebellar patients, the two prominent cinematic features are hypermetria and tremor. The stretch response is of the same latency, but the EMG pattern is modified with bursts of activity related to the tremor. These results show severe perturbations of load compensating tasks in cerebellar patients. We discuss the possible role of the exaggeration of LLSR in both hypermetria and tremor.

The cerebellum: cortical processing and theory

Several advances over the past year have made necessary a complete re-evaluation of the function of the cerebellum and of the role of cerebellar synaptic plasticity. These advances include the discovery of parallel fiber induced long-term depression, the presence of normal motor coordination in the absence of cerebellar long-term depression in knock-out mice, and the strong activation of the cerebellar nuclei while sensory tasks are performed.