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 present their technical approach for placement of electrodes into the GPi in awake patients with dystonia, including the methodology used 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 who had various forms of dystonia were included in this study. Baseline neurological status and improvement in motor function resulting from DBS were measured using the Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS). Implantation of the DBS lead 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 is technically feasible in the awake state in most cases, with low morbidity rates. Spontaneous discharge rates of GPi neurons in dystonia are similar to those of globus pallidus externus neurons, such that the two nuclei must be distinguished by neuronal discharge patterns rather than by rates. Active electrode locations associated with robust improvement (> 50% decrease in BFMDRS score) were located near the intercommissural plane, at a mean distance of 3.7 mm from the pallidocapsular border. Patients with juvenile-onset primary dystonia and those with the tardive form benefited greatly from this procedure, whereas benefits for most secondary dystonias and the adult-onset craniocervical form of this disorder were more modest.