Bilateral Subthalamic Nucleus Stimulation for Parkinson's Disease: A Systematic Review of the Clinical Literature

OBJECTIVE: To evaluate the benefits and adverse effects of bilateral subthalamic nucleus stimulation in the treatment of Parkinson's disease (PD) by systematically reviewing the published literature. METHODS: A search of the PubMed database using the key words subthalamic, nucleus, and stimulation yielded 624 articles published between 1966 and December 2003. Only articles that included original, nonduplicated descriptions of patients with PD treated with bilateral subthalamic nucleus stimulation were selected for further analysis. RESULTS: A total of 38 studies from 34 neurosurgical centers in 13 countries were identified for critical review. The outcomes for 471 patients with PD treated with bilateral subthalamic nucleus stimulation were assessed according to the Unified Parkinson's Disease Rating Scale in both on-medication and off-medication conditions. With stimulation, Unified Parkinson's Disease Rating Scale motor scores in the off-medication condition improved by 50% after 6 months, 56% after 12 months, 51% after 2 years, and 49% after 5 years compared with preoperative off-medication scores. At 12 months of subthalamic nucleus stimulation, the mean improvement in tremor was 81%, in rigidity was 63%, in bradykinesia was 52%, in gait was 64%, and in postural instability was 69% when compared with preoperative off-medication subscores. On-medication dyskinesias were reduced by 94%, as assessed 12 months after stimulation using the Unified Parkinson's Disease Rating Scale IV complications of therapy score. There was an overall 52% reduction in the L-dopa-equivalent dose intake after 12 months of stimulation. Most adverse effects were mild to moderate. There was a 1 to 2%incidence of severe adverse effects (death or permanent neurological deficits related to intracerebral hemorrhages). Nineteen percent of the patients had adverse effects related to stimulation that could be reversed by changing stimulation parameters. There was a 9%incidence of adverse effects related to the hardware (infections, lead and pulse generator problems). CONCLUSION: Bilateral subthalamic nucleus stimulation is effective in the treatment of PD. Further refinements in patient selection and surgical technique may lessen the incidence of complications associated with this procedure.