Objective: To evaluate the effects of acute and chronic stimulation in the anteromedial part of the globus pallidus internus (GPi) on the symptoms of patients with Parkinson's disease.
Methods: Six patients with severe Parkinson's disease (Hoehn and Yahr stage 4-5 in "off" drug condition) with motor fluctuations and levodopa induced dyskinesia (LID) were operated on. Chronic electrodes were implanted in the anteromedial GPi bilaterally in five patients and unilaterally in one patient. The effect of stimulation via the four contacts for each electrode (n=11) was assessed postoperatively on the contralateral parkinsonian signs in the off condition and on the contralateral and ipsilateral LID in the "on" condition. The core assessement program for intracerebral transplantation protocol was performed before surgery and then 1, 3, and 6 months after surgery in on and off conditions and in on and off stimulation conditions.
Results: Stimulation performed postoperatively showed a significant improvement (p<0.05) by 47% (contralateral rigidity) and 32% (contralateral bradykinesia) when stimulation was applied through the distal contact. Levodopa induced dyskinesias were improved by 95% (contralateral LID) and by 66% (ipsilateral LID) when stimulation was applied through the distal contact. Six months after the surgery, GPi stimulation in the off condition led to a mean improvement in the motor score of UPDRS by 36%. The mean daily duration in the off state decreased by 52% (p<0.05). The mean duration of LIDs decreased by 68% (p<0.05) and their severity by 53% (p<0.05).
Conclusion: Chronic stimulation in the anteromedial GPi shows that this is a safe and effective treatment for advanced Parkinson's disease with benefit sustained for at least 6 months.