Quantification of Temporal and Spatial Accuracy of Alternating Arm Movements in Multiple Sclerosis Patients Treated with Deep Brain Stimulation of the Thalamic Ventralis Intermedius Nucleus (VIM)

Abstract

In patients with multiple sclerosis (MS) ataxia is a common symptom, which is barely influenced by pharmacological treatment. We studied whether stimulation of the thalamic ventralis intermedius nucleus (VIM) improves the performance of alternating forearm movements in MS patients. We investigated 6 patients with primary (n=1) or secondary (n=5) chronic progressive MS (age 36-66 years, median 41.5 years, median EDSS [expanded disability status scale] 6.5). Patients were seated in a chair with one arm abduced at right angles to the body. This arm was strapped into a splint with one fixed section for the upper arm and one movable section for the forearm. The latter allowed horizontal movements in the elbow joint. The patients had to perform rhythmic alternating flexion and extension movements in the elbow joint. The rhythm and spatial extent of movements were indicated acoustically by a click tone stimulator and by marks respectively. Six manoeuvres (spatial extents of 48 degrees , 83 degrees at frequencies of 0.9 Hz, 1.5 Hz, and 2.5 Hz each) had to be performed. A potentiometer converted the horizontal movements of the forearm into a variable voltage. Forearm movements were measured with and without contralateral VIM stimulation. In all patients, spatial accuracy of the alternating forearm movements improved significantly after the stimulation had been switched on. Temporal accuracy increased during VIM stimulation in 5 of 6 patients. In 1 of 6 patients the spatial but not the temporal movement accuracy improved during stimulation. During VIM stimulation, performance of alternating forearm movements improved significantly. This might indicate that VIM stimulation could be a therapeutic alternative in the treatment of upper limb ataxia in MS.