Object. The use of deep brain stimulation (DBS) of the subthalamic nucleus (STN) has been associated with a marked initial improvement in individuals with advanced Parkinson disease (PD). Few data are available on the long-term outcomes of this procedure, however, or whether the initial benefits are sustained over time. The authors present the long-term results of a cohort of 25 individuals who underwent bilateral DBS of the STN between 1996 and 2001 and were followed up for 1 year or longer after implantation of the stimulator.
Methods. Patients were evaluated at baseline and repeatedly after surgery by using the Unified Parkinson's Disease Rating Scale (UPDRS); the scale was applied to patients during periods in which antiparkinsonian medications were effective and periods when their effects had worn off. Postoperative UPDRS total scores and subscores, dyskinesia scores, and drug dosages were compared with baseline values, and changes in the patients' postoperative scores were evaluated to assess the possibility that the effect of DBS diminished over time.
In this cohort the median duration of follow-up review was 24 months (range 12–52 months). The combined (ADL and motor) total UPDRS score during the medication-off period improved after 1 year, decreasing by 42% relative to baseline (95% confidence interval [CI 35–50%], p < 0.001) and the motor score decreased by 48% (95% CI 42–55%, p < 0.001). These gains did diminish over time, although a sustained clinical benefit remained at the time of the last evaluation (41% improvement over baseline, 95% CI 31–50%; p < 0.001). Axial subscores at the time of the last evaluation showed only a trend toward improvement (p = 0.08), in contrast to scores for total tremor (p < 0.001), rigidity (p < 0.001), and bradykinesia (p = 0.003), for which highly significant differences from baseline were still present at the time of the last evaluation. Medication requirements diminished substantially, with total medication doses reduced by 38% (95% CI 27–48%, p < 0.001) at 1 year and 36% (95% CI 25–48%, p < 0.001) at the time of the last evaluation; this decrease may have accounted, at least in part, for the significant decrease of 46.4% (95% CI 20.2–72.5%, p = 0.007) in dyskinesia scores obtained by patients during the medication-on period. No preoperative demographic variable, such as the patient's age at the time of disease onset, age at surgery, sex, duration of disease before surgery, preoperative drug dosage, or preoperative severity of dyskinesia, was predictive of long-term outcome. The only predictor of a better outcome was the patient's preoperative response to levodopa.
Conclusions. In this group of patients with advanced PD who underwent bilateral DBS of the STN, sustained improvement in motor function was present a mean of 2 years after the procedure, and sustained reductions in drug requirements were also achieved. Improvements in tremor, rigidity, and bradykinesia were more marked and better sustained over time than improvements in axial symptoms. A good preoperative response to levodopa predicted a good response to surgery.