Stereotactic model of the electrical distribution within the internal globus pallidus during deep brain stimulation.

Deep brain stimulation (DBS) of the internal globus pallidus (GPi) is an established surgical technique for the treatment of movement disorders. The objective of this study was to propose a computational stereotactic model of the electrical distribution around the electrode within the targeted GPi in order to optimize parameter adjustment in clinical practice. The outline of the GPi can be defined precisely by using stereotactic magnetic resonance imaging (MRI) and from this it is possible to model its three-dimensional structure. The electrode and the distribution of the patient-specific parameters can then be co-registered with the GPi volume. By using this methodology, it is possible to visualize and measure the relationship between the electrical distribution of patient-specific parameters and the morphology of the GPi. The model could be applied in clinical practice to help determine the threshold for achieving a therapeutic effect and consequently may aid in optimizing parameter settings for individual patients.

Prognostic value of globus pallidus internus volume in primary dystonia treated by deep brain stimulation.

OBJECT: Given that improvement is variable from one patient to another, the authors analyzed the impact of globus pallidus internus (GPi) volume on the result of deep brain stimulation (DBS) by comparing highly and less improved patients with primary dystonodyskinetic syndromes. METHODS: A stereotactic model was developed to visualize and quantify the relationship between the isofield lines generated by the DBS lead and GPi target. The model was used in 30 right-handed selected patients with primary dystonodyskinetic syndromes who had been treated using bilateral stimulation of the sensorimotor GPi. Ten healthy control individuals were also included in the study. First, the authors compared the GPi volumes between patients and healthy controls. Second, the stimulated GPi volumes, that is, the intersection between the volume of each isofield value and the GPi volumes, were compared between less improved and highly improved patients. RESULTS: Improvement in the Burke-Fahn-Marsden Dystonia Rating Scale's motor score was rated > 90% in 20 patients (97 +/- 4.6%) and < 60% in 10 patients (56.9 +/- 6%). The mean volume of the right (461.8 +/- 81.8 mm(3)) and left (406.6 +/- 113.2 mm(3)) GPi in patients showing less response to DBS was significantly smaller than the GPi volume of patients who responded well (right 539.9 +/- 86.6 mm(3), left 510.6 +/- 88.7 mm(3)) and healthy controls (right 557.8 +/- 109.1 mm(3), left 525.1 +/- 40.8 mm(3)). CONCLUSIONS: On the left side, the mean stimulated volumes (isofield line range 0.2-1 V/mm) were significantly larger in highly improved than in less improved patients. In this model, the threshold for functional effect was calculated at 0.2 V/mm.