Surgery targeting the internal segment of the globus pallidus has been shown to improve all of the cardinal features of PD including bradykinesia, rigidity, and tremor as well as levodopa-induced dyskinesia. Due to concerns of complications related to speech, balance, and cognition with bilateral pallidal lesions, bilateral DBS of the GPi is preferred to pallidotomy. Multiple studies have reported the efficacy of GPi stimulation for PD (15-20) (Table 1). Many of these studies have a small number of patients and/or a relatively short follow-up period.
Kumar et al. (19) reported 22 PD patients who were treated with either unilateral (n = 5) or bilateral (n = 17) GPi stimulation. Evaluations performed in the medication off/stimulation on state at six months reported a 32% improvement in UPDRS motor scores and a 40% improvement in UPDRS activities of daily living (ADL) scores compared to baseline medication off scores. There was also a 68% reduction in dyskinesia. The Deep Brain Stimulation for Parkinson's Disease Study Group (16) reported a multinational, prospective study of bilateral GPi stimulation in PD. Forty-one patients were enrolled and electrodes were implanted in 38 patients. Two patients had cerebral hemorrhages and one patient had intraoperative confusion. In comparison to baseline, there was a significant improvement of 33% in UPDRS motor scores in the medication off/stimulation on state. More specifically, tremor was reduced by 59%, rigidity was reduced 31%, bradykinesia was reduced 26%, gait improved by 35%, and postural instability improved by 36%. Patient diaries revealed that the percentage of on time without dyskinesia increased from 28% to 64% and daily off time was reduced from 37% to 24%. The mean daily dose of levodopa equivalents was unchanged between baseline and six months.
Several studies have examined the long-term benefits of DBS of the GPi (Table 1). Anderson et al. (21) reported 10 PD patients one year after bilateral GPi DBS.
TABLE 1 Selected Studies of Deep Brain Stimulation of the Globus Pallidus Interna
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