P 88 Using navigated Transcranial Magnetic Stimulation to identify the spatio-functional cortical representation of muscles innervated by the accessory nerve – a pilot study

Abstract

Introduction: The accessory nerve is frequently affected by iatrogenic injury which may cause major disability due to a loss of function in the trapezius muscle (trap) and/or the sternocleidomastoid muscle (scm). Navigated transcranial magnetic stimulation (nTMS) may be a valuable tool to quantify aspects of cortical motor reorganization and support decision making for timing of reconstructive surgery in nerval injury. Our study aims to delineate the spatio-functional cortical representation of muscles innervated by the accessory nerve in healthy volunteers. Patients & Methods: nTMS was used to stimulate the motor cortex on both hemispheres in four healthy volunteers to determine the spatio-functional cortical representation of the scm, trap, deltoid, biceps, first dorsalis interosseus (fdi) and zygomatic major (zm) muscles. In detail, the centre of gravity (CoG), the resting motor threshold (RMT), motor area (area), the recruitment curve (RC) and the cortical silent period (CSP) were examined. Statistical analysis was performed with GraphPad Prism using the nonparametric Mann Whithney U test. Results: The CoG of the scm was located between the CoG of the face (zm) and the CoG of the hand (fdi). The CoG of the trap was located superiorly to the CoG of the hand. Distances to the lateral sulcus differed significantly (scm: 23 mm, trap: 42 mm, p=0.03). The scm had a larger cortical representation area than the trap (median: 928 vs. 431 mm 2 for the right hemisphere (rh) and 522 vs. 171 mm 2 for the left hemisphere (lh); p = 0.03 and p = 0.03, respectively). The RMT (in V/m) of the scm and trap were 108 and 96 in the rh and 101 and 92 in the lh. Conclusion: This pilot-study describes the detailed spatio-functional representation of the trap and scm within the precentral gyrus according to the homuncular organization of the motor cortex. The scm has a larger cortical representation area than the trap. Our data shows feasibility of the technique and may serve as a baseline for future studies on patients with accessory nerve injury.