OBJECTIVE The posterior subthalamic area (PSA) is a promising target of deep brain stimulation (DBS) for medication-refractory essential tremor (ET). This case series describes a novel adverse effect manifesting as dystonic tics in patients with ET undergoing DBS of the PSA. METHODS Six patients with ET received electrode implants for DBS of the dorsal and caudal zona incerta subregions of the PSA. RESULTS Five of the 6 patients developed dystonic tics soon after clinical programming. These tics were of varying severity and required reduction of the electrical stimulation amplitude. This reduction resolved tic occurrence without significantly affecting ET control. Dystonic tics were not observed in 39 additional patients who underwent DBS of the same brain regions for controlling non-ET movement disorders. CONCLUSIONS The pathophysiology of tic disorders is poorly understood and may involve the basal ganglia and related cortico-striato-thalamo-cortical circuits. This series is the first report of DBS-induced tics after stimulation of any brain target. Although the PSA has not previously been implicated in tic pathophysiology, it may be a candidate region for future studies.
Keywords: DBS = deep brain stimulation; DSM-5 = Diagnostic and Statistical Manual of Mental Disorders, 5th Edition; ET = essential tremor; PSA = posterior subthalamic area; cZI = caudal zona incerta; dZI = dorsal zona incerta; deep brain stimulation; dystonic tic; essential tremor; functional neurosurgery; tic disorders.