Microelectrode-guided implantation of deep brain stimulators into the globus pallidus internus for dystonia: techniques, electrode locations, and outcomes

Object. Deep brain stimulation (DBS) of the globus pallidus internus (GPI) is a promising new procedure for the treatment of dystonia. The authors describe their technical approach for placing electrodes into the GPI in awake patients with dystonia, including methodology for electrophysiological mapping of the GPI in the dystonic state, clinical outcomes and complications, and the location of electrodes associated with optimal benefit. Methods. Twenty-three adult and pediatric patients with various forms of dystonia were included in this study. Baseline neurological status and DBS-related improvement in motor function were measured using the Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS). The implantation of DBS leads was performed using magnetic resonance (MR) imaging-based stereotaxy, single-cell microelectrode recording, and intraoperative test stimulation to determine thresholds for stimulation-induced adverse effects. Electrode locations were measured on computationally reformatted postoperative MR images according to a prospective protocol. Conclusions. Physiologically guided implantation of DBS electrodes in patients with dystonia was technically feasible in the awake state in most patients, and the morbidity rate was low. Spontaneous discharge rates of GPI neurons in dystonia were similar to those of globus pallidus extemus neurons, such that the two nuclei must be distinguished by neuronal discharge patterns rather than rates. Active electrode locations associated with robust improvement (> 70% decrease in BFMDRS score) were located near the intercommissural plane, at a mean distance from the pallidocapsular border of 3.6 mm.