Efficacies of globus pallidus stimulation and subthalamic nucleus stimulation for advanced Parkinson's disease: a meta-analysis of randomized controlled trials

Objectives: Deep brain stimulation (DBS) is the surgical procedure for patients with advanced Parkinson's disease. Globus pallidus internus (GPi) and subthalamic nucleus (STN) are the most targeted locations for the procedure. To investigate the variable efficiencies for the two different locations, we conducted a meta-analysis to compare both stimulation sites. Materials and methods: A systematic search was performed in PubMed, Embase, and the Cochrane Library databases. Randomized controlled trials comparing the efficacies of GPi and STN DBS were included. Clinical outcomes of motor function, nonmotor function, and quality of life (QOL) were collected for the meta-analysis. Results: Ten eligible trials with 1,034 patients were included in the analysis. Unified Parkinson's disease rating scale III (UPDRS-III) scores were collected at 6, 12, and 24 months postsurgery separately to assess the motor function of the patients. A statistically significant effect in favor of the GPi DBS was obtained in the off-medication/on-stimulation phase of UPDRS-III at 12 months (mean difference [MD] =6.87, 95% confidence interval [95% CI]: 3.00-10.74, P=0.57, I-2=0%). However, GPi DBS showed an opposite result at 24 months (MD=-2.46, 95% CI: -4.91 to -0.02, P=0.05, I-2=0%). In the on-medication/on-stimulation phase, GPi DBS obtained a worse outcome compared with STN DBS (MD=-2.90, 95% CI: -5.71 to -0.09, P=0.05, I-2=0%). Compared with STN DBS, increased dosage of levodopa equivalent doses was needed in GPi DBS (standardized MD=0.60, 95% CI: 0.46-0.74, P < 0.00001, I-2=24%). Meanwhile, Beck Depression Inventory II scores demonstrated that STN has a better performance (standardized MD=-0.31, 95% CI: -0.51 to -0.12, P=0.002, I-2=0%). As for neurocognitive phase postsurgery, GPi DBS showed better performance in three of the nine tests, especially in verbal fluency. Use of GPi DBS was associated with a greater effect in eight of the nine subscales of QOL. Conclusion: GPi and STN DBS significantly improve advanced Parkinson's patients' symptoms, functionality, and QOL. Variable therapeutic efficiencies were observed in both procedures, GPi and STN DBS. GPi DBS allowed greater recovery of verbal fluency and provided greater relief of depression symptoms. Better QOL was also obtained using GPi DBS. Meanwhile, GPi DBS was also associated with increased dosage of levodopa equivalent doses. The question regarding which target is superior remained open for discussion. An understanding of the target selection still depends on individual symptoms, neurocognitive/mood status, therapeutic goals of DBS (eg, levodopa reduction), and surgical expertise.