Distal versus proximal arm tremor in multiple sclerosis assessed by visually guided tracking tasks

Objectives-To compare action tremor (AT) during manual tracking in normal s ubjects and patients with multiple sclerosis with tremor (MS-tremor group) and without tremor (MS-no tremor group), and to differentiate tremor occurr ing predominantly around the distal joint from that involving the proximal joints of the arm. Methods-Subjects performed both a visually guided ramp tracking task using wrist flexion/extension and a whole arm circle tracking task using shoulder movement. Action tremor at the wrist or shoulder was computed as the SD of the tracking velocity. The ratio of wrist:arm tremor was then calculated t o differentiate distal from proximal tremor in the tested arm. Frequency sp ectra of the records were also examined. Results-During wrist tracking, AT in patients with multiple sclerosis conta ined a major frequency component at 4-5 Hz; the frequency was slightly lowe r during whole arm tracking. The ratio of wrist:arm tremor was significantl y higher in the MS-tremor group. Of 12 tested arms, eight had tremor signif icantly weighted towards the distal joint, only one towards the proximal jo int, and three had a ratio inside the control range. Conclusions-AT in the arms of patients with multiple sclerosis can be effec tively differentiated into proximal or distal using these two different tra cking tasks. Despite the variability of the effects of multiple sclerosis, most of the AT was distal rather than proximal in this group of patients. P ossibly conduction block along the cortico cerebellocortical pathways cause d this distal tremor.