Constant current stimulation may improve apraxia of eyelid opening induced by deep brain stimulation

Background: Apraxia of eyelid opening (AEO) is a common side effect of subthalamic nucleus deep brain stimulation (STN-DBS) and difficult to treat. We report the case of a patient with Parkinson's disease (PD) whose DBS-induced AEO was alleviated after adjustment from constant-voltage (CV) to constant-current (CC) stimulation. Case description: A female patient with PD underwent bilateral STN-DBS surgery 12 years after onset. Three months after the start of stimulation, she developed bilateral AEO though her motor symptoms improved. Her AEO severity deteriorated in line with an increase in stimulation-voltage. Three years after surgery, we replaced the implantable pulse generators (IPGs) because of low voltage. We changed the stimulation programs from CV stimulation to CC stimulation as only CC stimulation was available on the new IPG model. Her AEO was significantly improved after the stimulation programs were changed from CV to CC stimulation, even though the stimulation intensity did not change markedly. Her motor symptoms did not change. We evaluated the association between AEO severity and stimulation contact point and found that stimulation at the lowest contact on the left side strongly induced AEO. Conclusion: Shifting from CV stimulation to CC stimulation may improve DBS-induced AEO. The exact mechanism underlying this improvement is unknown and further studies are needed to confirm the efficacy of CC stimulation for AEO