In vivo modeling of acute external superior laryngeal nerve denervation using lidocaine block
Creators: name: Barton, Michael Eric
Publisher: name: University of Utah
Year: 2012
Subjects: Larynx--Innervation
Cricothyroid muscle

description: The external branch of the superior laryngeal nerve (ESLN) innervates the  cricothyroid (CT) muscle of the larynx, a vocal fold tensor primarily responsible for pitch  elevation. For over 100 years, a controversy has existed regarding the laryngeal signs that  should be considered pathognomonic of unilateral ESLN paralysis. Regrettably, little  progress has been made in resolving this controversy, as the extant clinical literature is  characterized by contradiction and inconsistency. Myriad descriptions exist of the  laryngeal behaviors ostensibly associated with unilateral ESLN denervation. To address  this longstanding controversy and improve diagnostic precision, this preliminary  investigation aimed to model "in vivo" acute, unilateral CT dysfunction by temporarily  blocking the ESLN using lidocaine hydrochloride (HCL), and verifying selective  denervation using laryngeal electromyography (LEMG). The purpose of this  investigation was twofold: (1) to identify the salient laryngeal features associated with  acute denervation (i.e., the pathognomonic features of unilateral CT dysfunction), and (2)  to identify a set of laryngeal tasks that maximally provoke or reveal ESLN dysfunction,  thereby contributing to a set of diagnostic tasks/markers that will improve diagnostic  accuracy during clinical assessment.  Ten vocally normal adult males (mean age = 25 yrs.; range = 19 to 29 years)  underwent lidocaine block of the right ESLN, and flexible videolaryngostroboscopic  (FVLS) recordings were acquired before and during the block. Eleven blinded, expert judges (6 laryngologists and 5 Ph.D. speech-language pathologists) rated randomized,  pre- vs. during-block recordings of 10 vocal tasks using standard FVLS rating protocols.  Contrary to clinical reports, no evidence of hypomobility/sluggishness of the ipsilateral  vocal fold, or a reliable pattern of axial rotation of the larynx during high pitch voice was  observed. Furthermore, no evidence was observed to support reduced vocal fold  longitudinal tension, aryepiglottic fold length asymmetry, phase asymmetry, vocal fold  plane differences, or glottic insufficiency, as diagnostic features of unilateral CT  dysfunction. Instead, the analysis revealed (1) a pattern of deviation of the petiole of the  epiglottis to the side of weakness (i.e., the right) in 60% of participants during a glissando  up maneuver produced at normal volume, and (2) a pattern of axial rotation of the  posterior commissure to the left and the anterior commissure to right in 50% of  participants during a maneuver which rapidly alternated between a maximum vocal fold  abduction task (Sniff) and a high-pitched "ee" production. Both of these findings have  not been previously reported elsewhere, and potentially represent new diagnostic markers  of unilateral CT paralysis. The results are discussed with respect to their clinical  implications, and the necessity to explore both females and clinical populations to better  appreciate the clinical utility of these diagnostic signs.