Effect of bilateral subthalamic nucleus stimulation on balance and finger control in Parkinson's disease

We aimed to quantify the effects of bilateral subthalamic nucleus (STN) stimulation in Parkinson's disease (PD) on stance and gait ("axial"motor control), and related this to effects on finger movements ("appendicular" motor control). Fourteen PD patients and 20 matched controls participated. Subjects completed several balance and gait tasks (standing with eyes open or closed, on a normal or foam surface; retropulsion test; walking with eyes closed; walking up and down stairs; Get Up and Go test). Postural control was quantified using trunk sway measurements (angle and angular velocity) in the roll and pitch directions. Subjects further performed a pinch grip reaction time task, where we measured isometric grip forces, as well as movement and reaction times. Patients were examined with STN stimulators switched on or off (order randomised across patients), always after a supramaximal levodopa dosage. STN stimulation improved postural control, as reflected by a reduced trunk sway tremor during stance, a reduced duration for all gait tasks, an increased trunk pitch velocity while rising from a chair, and improved roll stability. STN stimulation also improved finger control, as reflected by a reduced time to reach maximum grip force, without altering reaction times and maximum force levels. Improvements in finger control timing did not correlate with reduced task durations during gait. We conclude that STN stimulation affords improvement of postural control in PD, over and above optimal drug treatment. STN stimulation also provides a simultaneous effect on distal and axial motor control. Because improvements in distal and axial motor control were not correlated, we assume that these effects are mediated by stimulation of different structures within the STN.