Deep brain stimulation of the subthalamic nucleus is an effective treatment for advanced Parkinson's disease. The benefits of bilateral subthalamic stimulation are well documented, and some studies reported outcomes with a follow-up of 5 to 6 years; nevertheless, few data are available beyond 5 years. We report a long-term prospective evaluation of 14 consecutive parkinsonian patients, treated by bilateral subthalamic stimulation for at least 9 years. Motor symptoms, activity of daily living, and motor complications were evaluated by means of the Unified Parkinson's Disease Rating Scale, while cognition and mood were assessed with a specific neuropsychological test battery; medication intake, stimulation parameters, comorbidity, and adverse events were also recorded. Patients were evaluated before surgery and at 1, 5, and ≥ 9 years after surgery. At last follow-up, deep brain stimulation significantly improved the motor score by 42% compared to baseline, whereas activities of daily living were no longer improved; there was a 39% reduction in the dosage of dopaminergic drugs and a 59% improvement of L-dopa-related motor complications. The neuropsychological assessment showed that 4 patients (29%) developed a significant cognitive decline over the follow-up period. These results indicate a persistent effect of deep brain stimulation of the subthalamic nucleus on the cardinal motor symptoms in advanced Parkinson's disease patients in the long-term; however, a worsening of patients' disability, mainly due to disease progression, was observed.
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