Direct Optic Tract Stimulation in Deep Brain Stimulation for Dystonia: A Case Report

Abstract Deep brain stimulation (DBS) of the globus pallidus internus (GPi) is an effective therapeutic option for patients with medically refractory dystonia. However, accurate electrode placement is critical, particularly when the trajectory lies close to eloquent structures such as the optic radiations. Intraoperative neurophysiological monitoring using visual evoked potentials (VEPs) can aid in functional localization of the optic tract and enhance targeting accuracy. We report the case of a 62-year-old female with severe oromandibular dystonia and feeding impairment who underwent bilateral GPi DBS under general anesthesia with intraoperative VEP guidance. Cortical VEPs were first obtained using photic stimulation to confirm signal integrity and guide anesthetic titration. Direct optic tract stimulation was then performed using a 2-mm active-tip DBS electrode, with optic tract VEPs (oVEP) recorded to identify proximity to the optic tract. Microelectrode recordings and macrostimulation were used to identify dystonic firing patterns and confirm safe distance from the internal capsule. Final lead placement was guided by the site of maximal oVEP amplitude. Anesthetic depth was maintained at a bispectral index of 70 to 80 using dexmedetomidine, propofol, and desflurane, with careful opioid titration to preserve neurophysiological signals. The patient recovered without complications or awareness and remained neurologically stable postoperatively. This case highlights the feasibility of performing DBS under general anesthesia with intraoperative VEP guidance and emphasizes the importance of individualized anesthetic management and multidisciplinary coordination in complex movement disorder surgeries.