How deep brain stimulation and levodopa affect gait variability in Parkinson’s disease

Background Disorders of gait are a very common feature of Parkinson’s Disease. We examined how deep brain stimulation of the subthalamic nucleus (STN DBS) and dopaminergic medication affect gait and more specifically its rhythmicity. Objectives We accurately quantified multiple gait parameters in Parkinson’s patients during on and off stages of their treatment (levodopa or STN DBS) to compare and contrast the treatment-induced changes in gait. Methods We studied 11 patients with STN DBS, 15 patients on levodopa and 42 healthy controls. They all completed the MDS-UPDRS part III along with a gait assessment protocol while wearing six nine-axis inertial measurement units (lumbar, sternal, and all four extremities). Results Both medication and stimulation significantly improved stride length, while medication further significantly increased gait speed. In the lower limbs, both medication and stimulation had a normalising effect on lower limb angles, significantly increasing the foot strike angle and toe-off angle. Conclusions STN DBS reduced the step to step variability in a range of lower limb gait parameters in PD, while antiparkinsonian medication had no significant effect. This suggests that STN stimulation, but not dopaminergic medication, has access to circuits that control gait rhythm, and that the resulting effect of stimulation on gait is beneficial. However, the results we observed for movement of the trunk and upper limbs were strikingly different to those seen in the lower limbs. We propose a hypothesis to explain why we observe these results, focusing on cholinergic pedunculopontine projections.