Acute deep-brain stimulation of the internal and external globus pallidus in primary dystonia

Background: Dystonia is a syndrome characterized by prolonged muscle contractions that cause sustained twisting movements and abnormal posturing of body parts. Patients with the severe and generalized forms can benefit from bilateral high-frequency pallidal stimulation. Objective: To investigate the functional map of the globus pallidus (GP) in patients with primary generalized dystonia. Design: Prospective multicenter, double-blind, video-controlled study in patients treated at a university hospital. Setting: University secondary care centers. Patients: Twenty-two patients with primary generalized dystonia. Interventions: Acute internal and external pallidal deep-brain stimulation or pallidal deep-brain stimulation. Main Outcome Measures: The clinical effects of acute bilateral high-frequency ventral vs acute dorsal pallidal stimulation were assessed with the Movement subscale of the Burke-Fahn-Marsden Dystonia Rating Scale. Intrapallidal localization of the contacts of the quadri-polar electrodes was performed using a 3-dimensional atlas - magnetic resonance imaging coregistration method by investigators blinded to the clinical outcome. Results: Bilateral acute ventral stimulation of the GP significantly improved the Burke-Fahn-Marsden Dystonia Rating Scale score by 42% and resulted in stimulation of contacts located in the internal GP or medullary lamina in 18 of 21 patients. Bilateral acute dorsal pallidal stimulation, primarily localized within the external GP, had variable effects across patients, with half demonstrating slight or no improvement or even aggravation of dystonia compared with baseline. Conclusions: Ventral pallidal stimulation, primarily of the internal GP or medullary lamina or both, is the optimal method for the treatment of dystonia. The varying effects across patients of bilateral acute dorsal pallidal stimulation, primarily of the external GP, suggest that unknown factors associated with dystonia could have a role in and contribute to the effects of the electrical stimulation.