Abstract
Tremor of the upper extremity is a significant cause of disability in some patients with multiple sclerosis (MS). The MS tremor is complex because it contains an ataxic intentional tremor component due to the involvement of the cerebellum and cerebellar outflow pathways by MS plaques, which makes the MS tremor, in general, less responsive to medications or deep brain stimulation (DBS) than those associated with essential tremor or Parkinson's disease. The cerebellar component has been thought to be the main reason for making DBS less effective, although it is not clear whether it is due to the lack of suppression of the ataxic tremor by DBS or else. The goal of this study was to clarify the effect of DBS on cerebellar tremor compared to non-cerebellar tremor in a patient with MS. By wearing an accelerometer on the index finger of each hand, we were able to quantitatively characterize kinetic tremor by frequency and amplitude, with cerebellar ataxia component on one hand and that without cerebellar component on the other hand, at the beginning and end of the hand movement approaching a target at DBS Off and On status. We found that cerebellar tremor surprisingly had as good a response to DBS as the tremor without a cerebellar component, but the function control on cerebellar tremor was not as good due to its distal oscillation, which made the amplitude of tremor increasingly greater as it approached the target. This explains why cerebellar tremor or MS tremor with cerebellar component has a poor functional transformation even with a good percentage of tremor control. This case study provides a better understanding of the effect of DBS on cerebellar tremor and MS tremor by using a wearable device, which could help future studies improve patient selection and outcome prediction for DBS treatment of this disabling tremor.
Highlights
Tremor of the upper extremity is one of the major causes of disability in multiple sclerosis (MS)
By visual inspection (Figure 2), the left hand in a non-MS nonDBS normal person as a control and the left hand in the patient with MS had no significant change in waveform at the end of the test compared to that at the beginning of the test, during both the deep brain stimulation (DBS) Off and DBS On states
By the amplitude and frequency analysis (Figure 3), the left hand had no significant change in amplitude and frequency at the end of the test compared to that at the beginning of the test, at both DBS Off and On states (Figure 3, left upper panel), the amplitude was reduced by about 60% at DBS On state (Figure 3, left lower panel)
Summary
Tremor of the upper extremity is one of the major causes of disability in multiple sclerosis (MS). The effect of deep brain stimulation (DBS) of a ventral intermediate nucleus (VIM) on the control of hand tremor in patients with MS is highly variable and, in general, the tremor is less responsive than those associated with ET or Parkinson’s disease (PD; Roy and Aziz, 2014), even in DBS targeting posterior subthalamic area (PSA) or caudal zona incerta (cZi; Xie et al, 2012a; Ramirez-Zamora et al, 2016), or combined targets (Oliveria et al, 2017). Even in those with improved tremor following surgery, the improvement does not always translate to improved functional status (Roy and Aziz, 2014)
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