Motor evoked potentials as a side effect biomarker for deep brain stimulation programming

ObjectivesTo determine if motor evoked potentials (mEP) - stimulation-induced muscle activation measured using electromyography - can serve as a biomarker of corticobulbar (CBT) and corticospinal (CST) tract activation for deep brain stimulation (DBS) programming. MethodsIn 12 patients with Parkinsons disease and subthalamic or pallidal DBS, contact mapping determined clinical motor side effect thresholds. For equivalent stimulation parameters, EMG was recorded from cranial and arm muscles to determine the presence, peak amplitudes and latencies of mEP. Clinical and mEP thresholds were compared and accuracy metrics calculated to assess similarity between mEP and reported side effects. ResultsThe mEP amplitudes increased with stimulation intensity. Latencies were shorter for cranial muscles, which were more likely to generate an mEP. Clinical and mEP thresholds were significantly correlated (R2 = 0.31; p=0.0006), although most mEP thresholds were lower than clinical side effect thresholds. The mEP accuracy in predicting side effects was 0.72, with a sensitivity of 0.68 and a specificity of 0.73. ConclusionsEMG-recorded mEP correlated well with clinical side effects, and mEP often indicated subclinical CBT and CST activations. SignificanceThis study characterizes motor potentials evoked by DBS and demonstrates their utility as an objective biomarker for motor side effect threshold detection during DBS programming. Highlights- Deep brain stimulation can activate corticospinal/bulbar tract and evoke motor potentials in muscles measurable by surface EMG - Motor evoked potential thresholds correlate significantly with clinical side effect thresholds but occur at lower stimulation intensities - Motor evoked potentials may be a useful side effect biomarker for deep brain stimulation programming