Long-term evaluation of gait initiation in six Parkinson's disease patients with bilateral subthalamic stimulation

Defined as the transient state between standing and walking, gait initiation is negatively affected in Parkinson's disease (PD), which often results in significant disability. Although deep brain stimulation (DBS) is the most common surgical procedure for PD, the long-term effects of DBS on gait initiation are not well studied. The present study evaluated the long-term effects of subthalamic nucleus (STN) DBS on the preparation phase of gait initiation using principal component (PC) analysis. Six patients with PD who had undergone STN DBS and 24 healthy control subjects were evaluated. PD subjects were assessed 11.3±10.3 (P1) and 78.9±10.6 (P2) months after surgery. PD subjects were tested with STN DBS in two conditions: without medication and with medication. PC analysis was applied separately for the vertical, anterior-posterior and medial-lateral components of ground reaction force (GRF) recorded during gait initiation. Three PC scores were chosen by the scree test for each GRF component and all these PC scores were used for calculating a standard distance between healthy controls and PD subjects. The Friedman test showed a significant difference in standard distance among conditions (P=0.004), with the post-hoc test recognizing differences among P1 conditions and P2 medication-on condition. The eigenvector loading factors pointed to major differences between PD conditions surrounding the maximum amplitude of vertical and anterior-posterior GRF. For the studied sample, all distances increased in the follow-up evaluation (P2) with and without medications, indicating a worsening in gait initiation after seven years.