| 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. |
