Diplopia associated with loop routing in deep brain stimulation: illustrative case

BACKGROUND: Deep brain stimulation (DBS) is a powerful surgical option for drug-resistant movement disorders; however, electromagnetic interference (EMI) from external sources poses a potential risk for implanted electronics. OBSERVATIONS: A 61-year-old woman with Parkinson’s disease originally had two implantable pulse generators (IPGs) for bilateral subthalamic DBS, which were then replaced with one dual-channel IPG routed in a loop. After the replacement surgery, with the same DBS programming as before the IPG replacement (bipolar setting for right, unipolar setting for left), the patient began to complain of transient paroxysmal diplopia. After multiple attempts to adjust the stimulation parameters, the diplopia was resolved by changing the left unipolar setting to a bipolar setting. At the authors’ institution, before the present case, four other patients had undergone IPG replacement with loop routing. None of these previous patients complained of diplopia; however, two of the four presented with diplopia in an experimental unipolar setting. LESSONS: Clinicians should be aware that loop-routed circuits may generate distortion of the stimulus field in DBS, even in the absence of external EMI sources.