An In Vivo Model of External Superior Laryngeal Nerve Paralysis: Laryngoscopic Findings

Objectives/Hypothesis: For over 100 years, a controversy has existed regarding the laryngeal signs that should be considered pathognomonic of unilateral external superior laryngeal nerve (ESLN) paralysis. By selectively blocking the ESLN using lidocaine, we attempted to identify the salient laryngeal features associated with acute, unilateral cricothyroid (CT) muscle dysfunction. Study Design: Prospective, repeated measures, experimental design. Methods: Ten vocally normal adult males underwent lidocaine block of the right ESLN with laryngeal electromyography verification. Flexible videolaryngostroboscopic (FVLS) recordings were acquired before and during the block. Eleven blinded, expert judges, rated randomized pre- versus during block recordings of 10 vocal tasks using standardized FVLS rating protocols. Results: Contrary to recent clinical reports, no evidence of hypomobility/sluggishness of the ipsilateral vocal fold, or a consistent pattern of axial rotation of the larynx was observed. Instead, the analysis revealed: 1) deviation of the petiole of the epiglottis to the side of weakness in 60% of participants during a glissando up maneuver produced at normal volume, and 2) axial rotation of the posterior commissure to the left and the anterior commissure to the 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. Conclusions: Neither of these laryngeal findings has been reported previously. They potentially represent valuable diagnostic markers of acute, unilateral CT paralysis. Clinical populations need to be explored to better appreciate the diagnostic value and precision of these laryngeal signs.