Denervation of the external branch of the superior laryngeal nerve: laryngeal and phonatory features.

PURPOSE OF REVIEW

The external branch of the superior laryngeal nerve (ESLN) innervates the cricothyroid muscle of the larynx, a vocal fold tensor primarily responsible for pitch elevation. A longstanding controversy is revisited regarding the laryngeal and phonatory signs that should be considered indicative of unilateral ESLN paralysis/paresis.

RECENT FINDINGS

Diagnosis of unilateral ESLN paralysis remains challenging. Despite advances in laryngeal electromyography and improved techniques to visualize the larynx, there is no consensus regarding whether any laryngoscopic or phonatory features should be considered pathognomonic. Laryngeal and voice manifestations may reflect the pure effects of unilateral ESLN dysfunction, or, alternatively, compensatory muscular adjustments in response to prolonged denervation. However, recent in-vivo modeling of ESLN paralysis combined with clinical case studies suggests that deviation of the petiole of the epiglottis to the side of cricothyroid muscle weakness (during high-pitch voice production) may represent a potentially valuable diagnostic sign of both acute and chronic unilateral ESLN denervation.

SUMMARY

The absence of reliable diagnostic laryngoscopic signs renders it difficult to determine the prevalence, impact, and treatment of unilateral cricothyroid muscle dysfunction. Research is necessary to assess the precision of epiglottic petiole deviation as a possible marker of unilateral ESLN denervation.