An MRI view of a ruptured dermoid cyst

Abstract

Abstract-As the population of patients treated with deep brain stimulation (DBS) grows and the patients age, more will require routine or emergent electrophysiologic tests. DBS artifact may render these uninterpretable, whereas stopping DBS may release symptoms that confound evaluation. The authors find that monopolar, but not bipolar, stimulation produces significant artifact during EKG, EEG, and polysomnography. NEUROLOGY 2006;66:268-270 6 Because of the growing prevalence of DBS and the aging of patients with DBS, more will require electrodiagnostic procedures (such as EKG, EEG, and polysomnography) for evaluation of acute or chronic disease. DBS generates electrical artifact, a confounder that may obscure important diagnostic information. It was recently shown that bipolar DBS produces far less electrical artifact than monopolar DBS in EKG. 7 The purpose of our investigation is to confirm these earlier findings and to compare artifact produced from bipolar and monopolar DBS in routine EKG, EEG, and PSG studies. Methods.Subjects. Subject A. A 67-year-old man with bilateral subthalamic nucleus (STN) DBS for tremor-dominant PD underwent voluntary EKG and EEG. The DBS electrodes (Medtronic model 3389) were connected to subclavicular pulse generators (Medtronic, Soletra). He was initially treated with monopolar configurations, but programming sessions over the next 2 years yielded optimal clinical effects with bipolar settings: 4.3 V, 160 Hz, contacts 3ϩ, 0Ϫ, pulse width 90 microseconds (right) and 120 microseconds (left).Following informed consent, standard EKG and EEG were obtained initially at baseline bipolar DBS settings (figures 1A and 2A), with DBS off (see figures 1B and 2B), followed by a monopolar configuration (0Ϫ, caseϩ, 3.0 V) (see figures 1C and 2C).Subject B. A 66-year-old man was treated effectively with a right thalamotomy and a left ventralis intermedius thalamic DBS for tremor. He developed postoperative hypervigilance that evolved into excessive daytime sleepiness and fractionated sleep.He was prepared for overnight polysomnography by setting DBS to a bipolar configuration (3ϩ, 0Ϫ, 120 microseconds, 160 Hz, 5.3 V).Results. Figure 1A shows the V2 lead trace clipped from the standard 12-lead EKG recorded during bipolar stimulation (see figure 1B during temporary discontinuation of DBS and figure 1C during monopolar stimulation). The bipolar configuration produced clinically insignificant artifact (see figure 1A) that was similar to the "DBS off" condition (see figure 1B). In contrast, monopolar settings produced a large-amplitude artifact on EKG that obscured the P and T waves and QRS complex on all leads, rendering the study uninterpretable (see figure 1C). Figure 2 shows samples of optimal, occipital wakeful EEG rhythm. The montage included channels with both long and short interelectrode distances. The EEG demonstrated interpretable signal during bipolar stimulation (see figure 2A) with minimal differences between bipolar mode and DBS off (see figure 2, A and B). Resting tremor was visibl...