Quantitative assessment of deep brain stimulation on tremor in multiple sclerosis disease

Background and Purpose: Multiple sclerosis (MS) is a chronic disease that gives rise to a
number of unpleasant symptoms that can be difficult to manage by conventional means. There are
some aspects of MS-related disability which can be improved by using Deep Brain Stimulation
(DBS); particularly movement disorders, such as tremor. The research aim is to study the effect
of DBS on MS tremor with a quantitative approach.
Methods: Raw tremor data was provided by the Surgical Center for Movement Disorders at
the University of British Columbia, Canada. The hand tremor signal was collected on 8 MS
subjects and 10 healthy individuals during finger-to-nose test (FNT) by using motion analysis
system. Patients executed the FNT with DBS OFF and ON. Nonlinear and statistical features
were extracted from tremor spectrum as tremor indexes. Tremor reduction by using DBS was
determined by classifying mentioned features into three groups of healthy, DBS ON and DBS
OFF.
Results: Several dominant peaks were observed in power spectrum of the recorded signals which
indicate MS tremor consists of several tremor subtypes due to different sites of demyelinating
lesions affecting cerebellum and its output pathways. Results of frequency analysis revealed
tremor spectrum dominant frequency in healthy group was significantly greater than for the
patients with DBS ON and OFF (p<0.05). Additionally, classification results demonstrated that
tremor of 6 patients out of 8 decreased significantly when their DBS was ON.
Conclusion: Overall, in 75% of patients with MS who suffered from tremor, thalamic DBS
significantly reduced their tremor. In addition, power spectrum dominant frequency has high
potential for a quantitative and objective measure of MS tremor.