Long-term clinical outcomes of bilateral GPi deep brain stimulation in advanced Parkinson's disease: 5 years and beyond.

OBJECTIVE: Few studies have reported long-term outcomes of globus pallidus internus (GPi) deep brain stimulation (DBS) in Parkinson's disease (PD). The authors aimed to investigate long-term outcomes of bilateral GPi DBS for 5 years and beyond for PD patients. METHODS: The authors retrospectively analyzed the clinical outcomes in 65 PD patients treated with bilateral GPi DBS at a single center. The outcome measures of motor symptoms and health-related quality of life (HRQoL) included the Unified Parkinson's Disease Rating Scale (UPDRS) and the Parkinson's Disease Questionnaire (PDQ-39). Scores at baseline were compared with those at 1, 3, 5, and 6-8 years after implantation using Wilcoxon signed-rank tests with α correction. RESULTS: GPi DBS significantly improved the off-medication UPDRS III total scores, UPDRS IV, and dyskinesia score at 1 year when compared with baseline (all p < 0.001). The off- and on-medication tremor scores, UPDRS IV, and dyskinesia scores showed moderate and sustained improvement (the ranges of the mean percentage improvement at each time point were 61%-75%, 30%-80%, 29%-40%, and 40%-65%, respectively) despite lacking statistical significance at long-term follow-up with diminishing sample sizes. The off-medication UPDRS III total scores did not show significant improvement at 5 years or later, primarily because of worsening in rigidity, akinesia, speech, gait, and postural stability scores. The on-medication UPDRS III total scores also worsened over time, with a significant worsening at 6-8 years when compared with baseline (p = 0.008). The HRQoL analyses based on the PDQ-39 revealed significant improvement in the activities of daily living and discomfort domains at 1 year (p = 0.003 and 0.006, respectively); however, all the domains showed gradual worsening at the later time points without reaching statistical significance. At 3 years, the communication domain showed significant worsening compared with baseline scores (p = 0.002). CONCLUSIONS: GPi DBS in PD patients in this single-center cohort was associated with sustained long-term benefits in the off- and on-medication tremor score and motor complications. HRQoL and the cardinal motor symptoms other than tremor may worsen gradually in the long term. When counseling patients, it is important to recognize that benefits in tremor and dyskinesia are expected to be most persistent following bilateral GPi DBS implantation.