Unilateral deep brain stimulation surgery in Parkinson's disease improves ipsilateral symptoms regardless of laterality.

Purpose: Researchers have consistently observed in right-handed individuals across normal and disease states that the 'dominant' left hemisphere has greater ipsilateral control of the left side than the right hemisphere has over the right. We sought to determine whether this ipsilateral influence of the dominant hemisphere reported in Parkinson's disease extends to treatments such as deep brain stimulation (DBS) and whether it affects outcome. We hypothesised that among Parkinson right-handers, unilateral left DBS would provide greater ipsilateral motor improvement compared with the ipsilateral motor improvement experienced on the right side.

Scope: A total of 73 Parkinson patients who underwent unilateral DBS of the subthalamic nucleus (STN) or globus palidus internus (GPi) participated. Left and right 'composite scores', were computed by separately adding all items on the left and right side from the motor section of the Unified Parkinson Disease Rating Scale. The change in the pre- and 4-month post-implantation score was the primary outcome measure. The mean motor scores improved by 4.96 ± 11.79 points (p < 0.001) post-surgery on the ipsilateral side of the DBS implantation. Regression analyses revealed that the side (left vs. right) and target (STN vs. GPi) did not significantly contribute in the effect of ipsilateral motor improvement (p = 0.3557).

Conclusion: While DBS on the 'dominant' left side failed to exert a greater ipsilateral influence compared with DBS on the non-dominant right side, significant ipsilateral motor improvements were observed after unilateral stimulation regardless of site of implantation and laterality.