Comparison between subthalamic nucleus and globus pallidus internus stimulation for postural performance in Parkinsonʹs disease

Nine subjects with Parkinsonʹs disease, five subjects with electrodes implanted in the subthalamic nucleus (STN) and four with electrodes in the globus pallidus internus (GPi), were compared with a population of ten age-matched control subjects. The measures studied include a set of summary statistic scores, two stochastic parameters, the distribution of the center of pressure (CoP) displacement angles under each foot, and the distribution of bilateral patterns of CoP displacement angles. A Bayes classifier was designed to monitor the trend of postural performance in patients, with different treatments. Results suggested that the selected measures were sensitive to Parkinsonian postural sway abnormalities and highlight differences in response to treatments. Deep brain stimulation restored a more normal postural sway and levodopa increased sway abnormalities. Furthermore, the selected measures appear to detect different responses to levodopa between the STN and GPi groups: the negative side effects of levodopa on posture were less severe for STN than for GPi patients, perhaps due to the decreased need for levodopa intake in STN subjects. The measures proposed in this preliminary study may be useful adjuncts to evaluate balance and postural control strategies in patients with Parkinsonʹs disease and may allow the comparison of DBS electrode sites, on stance posture.