title: MEP latency shift after implantation of deep brain stimulation systems in the subthalamic nucleus in patients with advanced Parkinson's disease.
abstract: Deep brain stimulation (DBS) into the subthalamic nucleus (STN) is a highly effective treatment for advanced Parkinson's disease (PD). The consequences of STN stimulation on intracortical and corticospinal excitability have been addressed in a few studies using transcranial magnetic stimulation (TMS). Although excitability measurements were compared between the STN stimulation OFF and ON condition, in these experiments, there are no longitudinal studies examining the impact of electrode implantation per se on motor excitability. Here, we explored the effects of STN electrode implantation on resting motor thresholds (RMT), motor evoked potential (MEP) recruitment curves, and MEP onset latencies on 2 consecutive days before and shortly after STN surgery with the stimulator switched off, thus avoiding the effects of chronic DBS on the motor system, in 8 PD patients not taking any dopaminergic medication. After surgery, RMT and MEP recruitment curves were unchanged. In contrast, MEP onset latencies were significantly shorter when examined in relaxed muscles but were unchanged under preactivation. We hypothesize that postoperatively TMS pulses induced small currents in scalp leads underneath the TMS coil connecting the external stimulator with STN electrodes leading to inadvertent stimulation of fast-conducting descending neural elements in the vicinity of the STN, thereby producing submotor threshold descending volleys. These "conditioning" volleys probably preactivated spinal motor neurons leading to earlier suprathreshold activation by the multiple corticospinal volleys produced by TMS of the motor cortex. These TMS effects need to be considered when interpreting results of excitability measurements in PD patients after implantation of STN electrodes.
authors.affiliation: Department of Neurology, University Medical Centre Hamburg-Eppendorf, Germany.
authors.forename: Ute
authors.initials: U
authors.lastname: Hidding
authors.forename: Tobias
authors.initials: T
authors.lastname: Bäumer
authors.forename: Hartwig Roman
authors.initials: HR
authors.lastname: Siebner
authors.forename: Cüneyt
authors.initials: C
authors.lastname: Demiralay
authors.forename: Carsten
authors.initials: C
authors.lastname: Buhmann
authors.forename: Thomas
authors.initials: T
authors.lastname: Weyh
authors.forename: Christian
authors.initials: C
authors.lastname: Moll
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Hamel
authors.forename: Alexander
authors.initials: A
authors.lastname: Münchau
mesh_terms: D000368:Aged; D046690:Deep Brain Stimulation; D004567:Electrodes, Implanted; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000503:physiopathology; D009046:Motor Neurons / Q000502:physiology; D010300:Parkinson Disease / Q000503:physiopathology / Q000534:rehabilitation*; D011446:Prospective Studies; D011712:Pyramidal Tracts / Q000503:physiopathology; D011930:Reaction Time / Q000502:physiology*; D012684:Sensory Thresholds / Q000502:physiology; D020531:Subthalamic Nucleus / Q000503:physiopathology*