The dynamics of finger tremor in multiple sclerosis is affected by whole body position

Abstract Multiple sclerosis (MS) is a disease that results in widespread damage to the nervous system. One consequence of this disease is the emergence of enhanced tremor. This study was designed to (1) compare the tremor responses of persons with MS to that of healthy adults and to (2) examine the impact of whole body position (i.e., seated/standing) on tremor. Bilateral postural tremor was recorded using accelerometers attached to each index finger. Results revealed some similarity of tremor between groups in regard to the principal features (e.g., presence of peaks in similar frequency ranges). However, significant differences were observed with tremor for the MS persons being of greater amplitude, more regular (lower ApEn) and more strongly coupled across limbs compared to the elderly. The effects of body position were consistent across all subjects, with tremor increasing significantly from sitting-to-standing. However, the tremor increase for the MS group was greater than the elderly. Overall, the tremor for MS group was negatively affected by both this disease process and the nature of the task being performed. This latter result indicates that tremor does not simply reflect the feed-forward output of the neuromotor system but that it is influenced by the task constraints.