Improvement of Kinaesthetic Deficits by Subthalamic Nucleus Stimulation in Parkinson's Disease

Recent studies have revealed that patients with Parkinson's disease (PD) exhibit kinaesthesic deficits. For example, they have higher perceptual thresholds in detecting passive elbow movements. Deep brain stimulation (DBS) of the subthalamic nucleus (STN) improves motor deficits in PD, but its effect on kinaesthesia is unknown. We have now examined how STN DBS affects the perception of limb position. 9 PD patients with bilateral chronic STN DBS and 7 controls were tested. The subject's forearm was moved passively (˜ 0.5 deg/s) while resting on a splint. A torque motor was mechanically connected to the splint, moving it at a constant speed causing either forearm flexion or extension. For each condition (ON or OFF stimulation), 40 flexion and 40 extension movements were recorded with elbow joint angular displacements of 0.2, 0.6, 1 up to 8. To account for order effects, a subset of the PD patients (n=5) was tested in the ON-stimulation state first, while the remaining patients were first examined during the OFF-stimulation state (n=4). A 1° displacement was detected in 78% of the trials and a 2° displacement in over 91% of the trials by the control subjects. In contrast, PD patients were clearly impaired in the correct detection of movement direction. During ON-stimulation they showed correct responses in 74% for 2° displacements. Deficits worsened when the DBS device was OFF with PD patients correctly detecting 2° displacements in only 60% of the trials. Thresholds for 75% correct responses were 0.9° for controls, 2.5° for PD patients when stimulation was OFF and 2.0° when stimulation was ON. We conclude that STN DBS may improve kinaesthesic deficits in PD, but does not lead to a full recovery of proprioceptive function. (Work supported by a grant from the DFG (MA 2209/3–1.)