Neurophysiological profiles of responders and nonresponders to hypoglossal nerve stimulation: a single-institution study

Study Objectives: Hypoglossal nerve stimulation (HGNS) is an effective alternative treatment for obstructive sleep apnea that acts by opening the airway via selective stimulation of nerve fibers that innervate tongue muscles that protrude (genioglossus) and stiffen the tongue (transverse and vertical) while avoiding nerve fibers that innervate tongue muscles that retract the tongue (styloglossus and hyoglossus). There remains a subset of postoperative patients who fail to adequately respond to HGNS, in some cases due to mixed activation of muscles that simultaneously protrude and retract the tongue. This study aims to characterize the relationship between neurophysiological data from individual tongue muscle activation during intraoperative electromyographic recordings and postoperative apnea-hypopnea index responses to HGNS. Methods: A single-institution review of 46 patients undergoing unilateral HGNS implantation for obstructive sleep apnea. Patients were separated into responders and nonresponders through comparison of pre and postoperative apnea-hypopnea index. Neurophysiological data included electromyographic responses of the genioglossus, styloglossus/hyoglossus, intrinsic/vertical, and hyoglossus (neck) muscles to intraoperative stimulation using unipolar (- to - and o to o) and bipolar (+ to +) settings. Results: The overall treatment success rate was 61% as determined by a postoperative apnea-hypopnea index < 20 events/h with a greater than 50% AHI reduction. We observed no statistically significant relationships between treatment response and individual muscle responses. However, we did note that increasing body mass index was correlated with worse postoperative responses. Conclusions: Although we noted a significant subgroup of clinical nonresponders to HGNS postoperatively, these patients were not found to exhibit significant inclusion of tongue retractors intraoperatively on neurophysiological analysis. Further research is needed to delineate additional phenotypic factors that may contribute to HGNS treatment responses.