Localization of clinically effective stimulating electrodes in the human subthalamic nucleus on magnetic resonance imaging

Long-term follow up of bilateral deep brain stimulation of the subthalamic nucleus in patients with advanced Parkinson disease

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.

Deep brain stimulation of the subthalamic nucleus in Parkinson's disease: evaluation of active electrode contacts

BACKGROUND

The subthalamic nucleus is the preferred target for deep brain stimulation in patients with advanced Parkinson's disease. The site of permanent stimulation is the subject of ongoing debate, as stimulation both within and adjacent to the subthalamic nucleus may be effective.

OBJECTIVE

To assess the position of active electrode contacts in relation to the dorsal margin of the subthalamic nucleus as determined by intraoperative microrecordings and magnetic resonance imaging (MRI).

METHODS

In 25 patients suffering from severe levodopa sensitive parkinsonism, deep brain stimulating electrodes (n = 49) were implanted following mapping of the subthalamic nucleus by microrecording and microstimulation along five parallel tracks. Postoperative stereotactic radiography and fusion of pre- and postoperative MRI studies were used to determine the stereotactic position relative to the midcommissural point of the most effective electrode contacts selected for permanent stimulation (n = 49). Intraoperative microrecordings were analysed retrospectively to define the dorsal margin of the subthalamic nucleus. In cases where the dorsal margin could be defined in at least three microrecording tracks (n = 37) it was correlated with the position of the active contact using an algorithm developed for direct three dimensional comparisons.

RESULTS

Stimulation of the subthalamic nucleus resulted in marked improvement in levodopa sensitive parkinsonian symptoms and levodopa induced dyskinesias, with significant improvement in UPDRS III scores. In several instances, projection of the electrode artefacts onto the T2 weighted MRI visualised subthalamic nucleus of individual patients suggested that the electrodes had passed through the subthalamic nucleus. When the actual position of active electrode contacts (n = 35) was correlated with the dorsal margin of the subthalamic nucleus as defined neurophysiologically, most contacts were located either in proximity (+/- 1.0 mm) to the dorsal border of the subthalamic nucleus (32.4%) or further dorsal within the subthalamic region (37.8%). The other active contacts (29.7%) were detected within the dorsal (sensorimotor) subthalamic nucleus. The average position of all active contacts (n = 49) was 12.8 mm (+/- 1.0) lateral, 1.9 mm (+/- 1.4) posterior, and 1.6 mm (+/- 2.1) ventral to the midcommissural point.

CONCLUSIONS

Subthalamic nucleus stimulation appears to be most effective in the border area between the upper subthalamic nucleus (sensorimotor part) and the subthalamic area containing the zona incerta, fields of Forel, and subthalamic nucleus projections.

Neuropsychology for movement disorders neurosurgery

The neuropsychologist plays a crucial role in three phases of the neurosurgical treatment of movement disorder patients, namely screening, outcome evaluation and research. In screening patients, the differential diagnosis of dementia, impact of depression or other psychiatric conditions, and the influence of disease and medication-induced symptoms on cognitive performance must be determined. Postoperatively, systematic evaluations elucidate the cognitive costs or benefits of the procedure. The neuropsychologist is then able to provide feedback and counselling to the professional staff, patient and family to inform management strategies. Neuropsychologists also study alteration of cognitive processing due to lesions or stimulation, which, in tandem with functional imaging, shed light on plasticity in cortical and subcortical processing.