Deep brain stimulation of the subthalamic nucleus represents the most important innovation for treatment of advanced Parkinson’s disease. Prospective studies have shown that although the beneficial effects of this procedure are maintained at 5 years, axial motor features and cognitive decline may occur in the long term after the implants. In order to address some unsolved questions raised by previous studies, we evaluated a series of 20 consecutive patients who received continuous stimulation for 8 years. The overall motor improvement reported at 5 years (55.5% at Unified Parkinson’s Disease Rating Scale—motor part, P < 0.001 compared with baseline) was only partly retained 3 years later (39%, P < 0.001, compared with baseline; −16.5%, P < 0.01, compared with 5 years), with differential effects on motor features: speech did not improve and postural stability worsened (P < 0.05). The preoperative levodopa equivalent daily dose was reduced by 58.2% at 5 years and by 60.3% at 8 years. In spite of subtle worsening of motor features, a dramatic impairment in functional state (−56.6% at Unified Parkinson’s Disease Rating Scale—Activities of Daily Living, P < 0.01) emerged after the fifth year of stimulation. The present study did not reveal a predictive value of preoperative levodopa response, whereas few single features at baseline (such as gait and postural stability motor scores and the preoperative levodopa equivalent daily dose) could predict long-term motor outcome. A decline in verbal fluency (slightly more pronounced than after 5 years) was detected after 8 years. A significant but slight decline in tasks of abstract reasoning, episodic memory and executive function was also found. One patient had developed dementia at 5 years with further progression at 8 years. Executive dysfunction correlated significantly with postural stability, suggesting interplay between axial motor deterioration and cognition. Eight years after surgery, no significant change was observed on scales assessing depression or anxiety when compared with baseline. At 8 years, there was no significant increase of side-effects when compared with 5-year follow-up. In conclusion, deep brain stimulation of the subthalamic nucleus is a safe procedure with regard to cognitive and behavioural morbidity over long-term follow-up. However, the global benefit partly decreases later in the course of the disease, due to progression of Parkinson’s disease and the appearance of medication- and stimulation-resistant symptoms.

Deep Brain Stimulation of the Subthalamic Nucleus (STN-DBS) is an effective treatment for Parkinson's disease (PD), but only few studies investigated its long-term efficacy. Furthermore, little is known about the role of PD-subtype on STN-DBS long-term outcome. To report the results of a long-term follow-up (mean 11 years, range 10-13) on 26 patients bilaterally implanted in two centres. Patients were assessed preoperatively and 1, 5 and 11 years after the implant by the Unified Parkinson's Disease Rating Scale (UPDRS) and a battery of neuropsychological tests. Stimulation parameters, drugs dosages, non-motor symptoms and adverse events were also recorded. At 11 years, stimulation significantly improved the motor symptoms by 35.8%, as compared to the preoperative off-state. Motor complications were well controlled, with a 84.6% improvement of dyskinesias and a 65.8% improvement of motor fluctuations. Despite this, the UPDRS-II-on score worsened by 88.5%, mainly for the worsening of poorly levodopa-responsive symptoms. More than 70% of the patients performed in the normal range in most of the neuropsychological tests, despite the development of dementia in 22.7%. Age at disease onset, axial subscore in off-condition and presence of REM behaviour disorder at baseline were found to be associated with a higher risk of developing disability over time. Our study confirms the long-term safety and efficacy of STN-DBS in PD. Nevertheless, the functionality of patients worsens over time, mainly for the onset and progression of levodopa-resistant and non-motor symptoms. The role of PD-subtype seems to be relevant in the long-term outcome.

S and full research articles published in SLEEP, the official journal of the APSS. Sleep and sleep disorder scientific findings.