Gait and postural instability in Parkinson's disease treated with deep brain stimulation of the subthalamic nucleus.

In late stage Parkinson's disease (PD), medical treatment may not control the symptoms adequately, and the patient may become eligible for bilateral high frequency deep brain stimulation (DBS) in the subthalamic nucleus (STN). The effect of STN DBS on gait and postural instability is not always as predictable as the effect on clinical symptoms tremor, rigidity and bradykinesia. This may relate to the type of gait disorder or the stimulating electrode localization in the STN. We sought to evaluate the effect of STN DBS on gait performance during overground walking and gait initiation--assessed with 3D optokinetic movement analyses--and to compare the DBS effect with stimulation site localized on peri-operative MRI. The stimulation sites were grouped according to STN borders visualised on pre-operative MRI, and the active stimulation site was compared with clinical improvement and gait parameters. STN DBS is associated with improved movement amplitude while movement duration may be unaffected by both disease and stimulation. This may imply an improvement primarily on hypokinesia including gait hypokinesia.